text: // Copyright 2012 the V8 project authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #include "src/execution/isolate.h"
  
  #include <stdlib.h>
  
  #include <atomic>
  #include <fstream>
  #include <memory>
  #include <sstream>
  #include <string>
  #include <unordered_map>
  #include <utility>
  
  #include "src/api/api-inl.h"
  #include "src/ast/ast-value-factory.h"
  #include "src/ast/scopes.h"
  #include "src/base/hashmap.h"
  #include "src/base/logging.h"
  #include "src/base/platform/mutex.h"
  #include "src/base/platform/platform.h"
  #include "src/base/sys-info.h"
  #include "src/base/utils/random-number-generator.h"
  #include "src/bigint/bigint.h"
  #include "src/builtins/builtins-promise.h"
  #include "src/builtins/constants-table-builder.h"
  #include "src/codegen/assembler-inl.h"
  #include "src/codegen/compilation-cache.h"
  #include "src/codegen/flush-instruction-cache.h"
  #include "src/common/assert-scope.h"
  #include "src/common/ptr-compr.h"
  #include "src/compiler-dispatcher/compiler-dispatcher.h"
  #include "src/compiler-dispatcher/optimizing-compile-dispatcher.h"
  #include "src/date/date.h"
  #include "src/debug/debug-frames.h"
  #include "src/debug/debug.h"
  #include "src/deoptimizer/deoptimizer.h"
  #include "src/deoptimizer/materialized-object-store.h"
  #include "src/diagnostics/basic-block-profiler.h"
  #include "src/diagnostics/compilation-statistics.h"
  #include "src/execution/frames-inl.h"
  #include "src/execution/isolate-inl.h"
  #include "src/execution/local-isolate.h"
  #include "src/execution/messages.h"
  #include "src/execution/microtask-queue.h"
  #include "src/execution/protectors-inl.h"
  #include "src/execution/runtime-profiler.h"
  #include "src/execution/simulator.h"
  #include "src/execution/v8threads.h"
  #include "src/execution/vm-state-inl.h"
  #include "src/handles/persistent-handles.h"
  #include "src/heap/heap-inl.h"
  #include "src/heap/read-only-heap.h"
  #include "src/ic/stub-cache.h"
  #include "src/init/bootstrapper.h"
  #include "src/init/setup-isolate.h"
  #include "src/init/v8.h"
  #include "src/interpreter/interpreter.h"
  #include "src/libsampler/sampler.h"
  #include "src/logging/counters.h"
  #include "src/logging/log.h"
  #include "src/logging/metrics.h"
  #include "src/numbers/hash-seed-inl.h"
  #include "src/objects/backing-store.h"
  #include "src/objects/elements.h"
  #include "src/objects/feedback-vector.h"
  #include "src/objects/hash-table-inl.h"
  #include "src/objects/js-array-buffer-inl.h"
  #include "src/objects/js-array-inl.h"
  #include "src/objects/js-generator-inl.h"
  #include "src/objects/js-weak-refs-inl.h"
  #include "src/objects/module-inl.h"
  #include "src/objects/promise-inl.h"
  #include "src/objects/prototype.h"
  #include "src/objects/slots.h"
  #include "src/objects/smi.h"
  #include "src/objects/source-text-module-inl.h"
  #include "src/objects/stack-frame-info-inl.h"
  #include "src/objects/visitors.h"
  #include "src/profiler/heap-profiler.h"
  #include "src/profiler/tracing-cpu-profiler.h"
  #include "src/regexp/regexp-stack.h"
  #include "src/snapshot/embedded/embedded-data.h"
  #include "src/snapshot/embedded/embedded-file-writer-interface.h"
  #include "src/snapshot/read-only-deserializer.h"
  #include "src/snapshot/startup-deserializer.h"
  #include "src/strings/string-builder-inl.h"
  #include "src/strings/string-stream.h"
  #include "src/tasks/cancelable-task.h"
  #include "src/tracing/tracing-category-observer.h"
  #include "src/trap-handler/trap-handler.h"
  #include "src/utils/address-map.h"
  #include "src/utils/ostreams.h"
  #include "src/utils/version.h"
  #include "src/zone/accounting-allocator.h"
  #include "src/zone/type-stats.h"
  #ifdef V8_INTL_SUPPORT
  #include "unicode/uobject.h"
  #endif  // V8_INTL_SUPPORT
  
  #if V8_ENABLE_WEBASSEMBLY
  #include "src/wasm/wasm-code-manager.h"
  #include "src/wasm/wasm-engine.h"
  #include "src/wasm/wasm-module.h"
  #include "src/wasm/wasm-objects.h"
  #endif  // V8_ENABLE_WEBASSEMBLY
  
  #if defined(V8_OS_WIN64)
  #include "src/diagnostics/unwinding-info-win64.h"
  #endif  // V8_OS_WIN64
  
  #ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
  #include "src/base/platform/wrappers.h"
  #include "src/heap/conservative-stack-visitor.h"
  #endif
  
  extern "C" const uint8_t* v8_Default_embedded_blob_code_;
  extern "C" uint32_t v8_Default_embedded_blob_code_size_;
  extern "C" const uint8_t* v8_Default_embedded_blob_data_;
  extern "C" uint32_t v8_Default_embedded_blob_data_size_;
  
  namespace v8 {
  namespace internal {
  
  #ifdef DEBUG
  #define TRACE_ISOLATE(tag)                                                  \
    do {                                                                      \
      if (FLAG_trace_isolates) {                                              \
        PrintF("Isolate %p (id %d)" #tag "\n", reinterpret_cast<void*>(this), \
               id());                                                         \
      }                                                                       \
    } while (false)
  #else
  #define TRACE_ISOLATE(tag)
  #endif
  
  const uint8_t* DefaultEmbeddedBlobCode() {
    return v8_Default_embedded_blob_code_;
  }
  uint32_t DefaultEmbeddedBlobCodeSize() {
    return v8_Default_embedded_blob_code_size_;
  }
  const uint8_t* DefaultEmbeddedBlobData() {
    return v8_Default_embedded_blob_data_;
  }
  uint32_t DefaultEmbeddedBlobDataSize() {
    return v8_Default_embedded_blob_data_size_;
  }
  
  #ifdef V8_MULTI_SNAPSHOTS
  extern "C" const uint8_t* v8_Trusted_embedded_blob_code_;
  extern "C" uint32_t v8_Trusted_embedded_blob_code_size_;
  extern "C" const uint8_t* v8_Trusted_embedded_blob_data_;
  extern "C" uint32_t v8_Trusted_embedded_blob_data_size_;
  
  const uint8_t* TrustedEmbeddedBlobCode() {
    return v8_Trusted_embedded_blob_code_;
  }
  uint32_t TrustedEmbeddedBlobCodeSize() {
    return v8_Trusted_embedded_blob_code_size_;
  }
  const uint8_t* TrustedEmbeddedBlobData() {
    return v8_Trusted_embedded_blob_data_;
  }
  uint32_t TrustedEmbeddedBlobDataSize() {
    return v8_Trusted_embedded_blob_data_size_;
  }
  #endif
  
  namespace {
  // These variables provide access to the current embedded blob without requiring
  // an isolate instance. This is needed e.g. by Code::InstructionStart, which may
  // not have access to an isolate but still needs to access the embedded blob.
  // The variables are initialized by each isolate in Init(). Writes and reads are
  // relaxed since we can guarantee that the current thread has initialized these
  // variables before accessing them. Different threads may race, but this is fine
  // since they all attempt to set the same values of the blob pointer and size.
  
  std::atomic<const uint8_t*> current_embedded_blob_code_(nullptr);
  std::atomic<uint32_t> current_embedded_blob_code_size_(0);
  std::atomic<const uint8_t*> current_embedded_blob_data_(nullptr);
  std::atomic<uint32_t> current_embedded_blob_data_size_(0);
  
  // The various workflows around embedded snapshots are fairly complex. We need
  // to support plain old snapshot builds, nosnap builds, and the requirements of
  // subtly different serialization tests. There's two related knobs to twiddle:
  //
  // - The default embedded blob may be overridden by setting the sticky embedded
  // blob. This is set automatically whenever we create a new embedded blob.
  //
  // - Lifecycle management can be either manual or set to refcounting.
  //
  // A few situations to demonstrate their use:
  //
  // - A plain old snapshot build neither overrides the default blob nor
  // refcounts.
  //
  // - mksnapshot sets the sticky blob and manually frees the embedded
  // blob once done.
  //
  // - Most serializer tests do the same.
  //
  // - Nosnapshot builds set the sticky blob and enable refcounting.
  
  // This mutex protects access to the following variables:
  // - sticky_embedded_blob_code_
  // - sticky_embedded_blob_code_size_
  // - sticky_embedded_blob_data_
  // - sticky_embedded_blob_data_size_
  // - enable_embedded_blob_refcounting_
  // - current_embedded_blob_refs_
  base::LazyMutex current_embedded_blob_refcount_mutex_ = LAZY_MUTEX_INITIALIZER;
  
  const uint8_t* sticky_embedded_blob_code_ = nullptr;
  uint32_t sticky_embedded_blob_code_size_ = 0;
  const uint8_t* sticky_embedded_blob_data_ = nullptr;
  uint32_t sticky_embedded_blob_data_size_ = 0;
  
  bool enable_embedded_blob_refcounting_ = true;
  int current_embedded_blob_refs_ = 0;
  
  const uint8_t* StickyEmbeddedBlobCode() { return sticky_embedded_blob_code_; }
  uint32_t StickyEmbeddedBlobCodeSize() {
    return sticky_embedded_blob_code_size_;
  }
  const uint8_t* StickyEmbeddedBlobData() { return sticky_embedded_blob_data_; }
  uint32_t StickyEmbeddedBlobDataSize() {
    return sticky_embedded_blob_data_size_;
  }
  
  void SetStickyEmbeddedBlob(const uint8_t* code, uint32_t code_size,
                             const uint8_t* data, uint32_t data_size) {
    sticky_embedded_blob_code_ = code;
    sticky_embedded_blob_code_size_ = code_size;
    sticky_embedded_blob_data_ = data;
    sticky_embedded_blob_data_size_ = data_size;
  }
  
  }  // namespace
  
  void DisableEmbeddedBlobRefcounting() {
    base::MutexGuard guard(current_embedded_blob_refcount_mutex_.Pointer());
    enable_embedded_blob_refcounting_ = false;
  }
  
  void FreeCurrentEmbeddedBlob() {
    CHECK(!enable_embedded_blob_refcounting_);
    base::MutexGuard guard(current_embedded_blob_refcount_mutex_.Pointer());
  
    if (StickyEmbeddedBlobCode() == nullptr) return;
  
    CHECK_EQ(StickyEmbeddedBlobCode(), Isolate::CurrentEmbeddedBlobCode());
    CHECK_EQ(StickyEmbeddedBlobData(), Isolate::CurrentEmbeddedBlobData());
  
    InstructionStream::FreeOffHeapInstructionStream(
        const_cast<uint8_t*>(Isolate::CurrentEmbeddedBlobCode()),
        Isolate::CurrentEmbeddedBlobCodeSize(),
        const_cast<uint8_t*>(Isolate::CurrentEmbeddedBlobData()),
        Isolate::CurrentEmbeddedBlobDataSize());
  
    current_embedded_blob_code_.store(nullptr, std::memory_order_relaxed);
    current_embedded_blob_code_size_.store(0, std::memory_order_relaxed);
    current_embedded_blob_data_.store(nullptr, std::memory_order_relaxed);
    current_embedded_blob_data_size_.store(0, std::memory_order_relaxed);
    sticky_embedded_blob_code_ = nullptr;
    sticky_embedded_blob_code_size_ = 0;
    sticky_embedded_blob_data_ = nullptr;
    sticky_embedded_blob_data_size_ = 0;
  }
  
  // static
  bool Isolate::CurrentEmbeddedBlobIsBinaryEmbedded() {
    // In some situations, we must be able to rely on the embedded blob being
    // immortal immovable. This is the case if the blob is binary-embedded.
    // See blob lifecycle controls above for descriptions of when the current
    // embedded blob may change (e.g. in tests or mksnapshot). If the blob is
    // binary-embedded, it is immortal immovable.
    const uint8_t* code =
        current_embedded_blob_code_.load(std::memory_order::memory_order_relaxed);
    if (code == nullptr) return false;
  #ifdef V8_MULTI_SNAPSHOTS
    if (code == TrustedEmbeddedBlobCode()) return true;
  #endif
    return code == DefaultEmbeddedBlobCode();
  }
  
  void Isolate::SetEmbeddedBlob(const uint8_t* code, uint32_t code_size,
                                const uint8_t* data, uint32_t data_size) {
    CHECK_NOT_NULL(code);
    CHECK_NOT_NULL(data);
  
    embedded_blob_code_ = code;
    embedded_blob_code_size_ = code_size;
    embedded_blob_data_ = data;
    embedded_blob_data_size_ = data_size;
    current_embedded_blob_code_.store(code, std::memory_order_relaxed);
    current_embedded_blob_code_size_.store(code_size, std::memory_order_relaxed);
    current_embedded_blob_data_.store(data, std::memory_order_relaxed);
    current_embedded_blob_data_size_.store(data_size, std::memory_order_relaxed);
  
  #ifdef DEBUG
    // Verify that the contents of the embedded blob are unchanged from
    // serialization-time, just to ensure the compiler isn't messing with us.
    EmbeddedData d = EmbeddedData::FromBlob();
    if (d.EmbeddedBlobDataHash() != d.CreateEmbeddedBlobDataHash()) {
      FATAL(
          "Embedded blob data section checksum verification failed. This "
          "indicates that the embedded blob has been modified since compilation "
          "time.");
    }
    if (FLAG_text_is_readable) {
      if (d.EmbeddedBlobCodeHash() != d.CreateEmbeddedBlobCodeHash()) {
        FATAL(
            "Embedded blob code section checksum verification failed. This "
            "indicates that the embedded blob has been modified since "
            "compilation time. A common cause is a debugging breakpoint set "
            "within builtin code.");
      }
    }
  #endif  // DEBUG
  }
  
  void Isolate::ClearEmbeddedBlob() {
    CHECK(enable_embedded_blob_refcounting_);
    CHECK_EQ(embedded_blob_code_, CurrentEmbeddedBlobCode());
    CHECK_EQ(embedded_blob_code_, StickyEmbeddedBlobCode());
    CHECK_EQ(embedded_blob_data_, CurrentEmbeddedBlobData());
    CHECK_EQ(embedded_blob_data_, StickyEmbeddedBlobData());
  
    embedded_blob_code_ = nullptr;
    embedded_blob_code_size_ = 0;
    embedded_blob_data_ = nullptr;
    embedded_blob_data_size_ = 0;
    current_embedded_blob_code_.store(nullptr, std::memory_order_relaxed);
    current_embedded_blob_code_size_.store(0, std::memory_order_relaxed);
    current_embedded_blob_data_.store(nullptr, std::memory_order_relaxed);
    current_embedded_blob_data_size_.store(0, std::memory_order_relaxed);
    sticky_embedded_blob_code_ = nullptr;
    sticky_embedded_blob_code_size_ = 0;
    sticky_embedded_blob_data_ = nullptr;
    sticky_embedded_blob_data_size_ = 0;
  }
  
  const uint8_t* Isolate::embedded_blob_code() const {
    return embedded_blob_code_;
  }
  uint32_t Isolate::embedded_blob_code_size() const {
    return embedded_blob_code_size_;
  }
  const uint8_t* Isolate::embedded_blob_data() const {
    return embedded_blob_data_;
  }
  uint32_t Isolate::embedded_blob_data_size() const {
    return embedded_blob_data_size_;
  }
  
  // static
  const uint8_t* Isolate::CurrentEmbeddedBlobCode() {
    return current_embedded_blob_code_.load(
        std::memory_order::memory_order_relaxed);
  }
  
  // static
  uint32_t Isolate::CurrentEmbeddedBlobCodeSize() {
    return current_embedded_blob_code_size_.load(
        std::memory_order::memory_order_relaxed);
  }
  
  // static
  const uint8_t* Isolate::CurrentEmbeddedBlobData() {
    return current_embedded_blob_data_.load(
        std::memory_order::memory_order_relaxed);
  }
  
  // static
  uint32_t Isolate::CurrentEmbeddedBlobDataSize() {
    return current_embedded_blob_data_size_.load(
        std::memory_order::memory_order_relaxed);
  }
  
  size_t Isolate::HashIsolateForEmbeddedBlob() {
    DCHECK(builtins_.is_initialized());
    DCHECK(Builtins::AllBuiltinsAreIsolateIndependent());
  
    DisallowGarbageCollection no_gc;
  
    static constexpr size_t kSeed = 0;
    size_t hash = kSeed;
  
    // Hash data sections of builtin code objects.
    for (int i = 0; i < Builtins::builtin_count; i++) {
      Code code = heap_.builtin(i);
  
      DCHECK(Internals::HasHeapObjectTag(code.ptr()));
      uint8_t* const code_ptr =
          reinterpret_cast<uint8_t*>(code.ptr() - kHeapObjectTag);
  
      // These static asserts ensure we don't miss relevant fields. We don't hash
      // instruction/metadata size and flags since they change when creating the
      // off-heap trampolines. Other data fields must remain the same.
      STATIC_ASSERT(Code::kInstructionSizeOffset == Code::kDataStart);
      STATIC_ASSERT(Code::kMetadataSizeOffset ==
                    Code::kInstructionSizeOffsetEnd + 1);
      STATIC_ASSERT(Code::kFlagsOffset == Code::kMetadataSizeOffsetEnd + 1);
      STATIC_ASSERT(Code::kBuiltinIndexOffset == Code::kFlagsOffsetEnd + 1);
      static constexpr int kStartOffset = Code::kBuiltinIndexOffset;
  
      for (int j = kStartOffset; j < Code::kUnalignedHeaderSize; j++) {
        hash = base::hash_combine(hash, size_t{code_ptr[j]});
      }
    }
  
    // The builtins constants table is also tightly tied to embedded builtins.
    hash = base::hash_combine(
        hash, static_cast<size_t>(heap_.builtins_constants_table().length()));
  
    return hash;
  }
  
  base::Thread::LocalStorageKey Isolate::isolate_key_;
  base::Thread::LocalStorageKey Isolate::per_isolate_thread_data_key_;
  #if DEBUG
  std::atomic<bool> Isolate::isolate_key_created_{false};
  #endif
  
  namespace {
  // A global counter for all generated Isolates, might overflow.
  std::atomic<int> isolate_counter{0};
  }  // namespace
  
  Isolate::PerIsolateThreadData*
  Isolate::FindOrAllocatePerThreadDataForThisThread() {
    ThreadId thread_id = ThreadId::Current();
    PerIsolateThreadData* per_thread = nullptr;
    {
      base::MutexGuard lock_guard(&thread_data_table_mutex_);
      per_thread = thread_data_table_.Lookup(thread_id);
      if (per_thread == nullptr) {
        if (FLAG_adjust_os_scheduling_parameters) {
          base::OS::AdjustSchedulingParams();
        }
        per_thread = new PerIsolateThreadData(this, thread_id);
        thread_data_table_.Insert(per_thread);
      }
      DCHECK(thread_data_table_.Lookup(thread_id) == per_thread);
    }
    return per_thread;
  }
  
  void Isolate::DiscardPerThreadDataForThisThread() {
    ThreadId thread_id = ThreadId::TryGetCurrent();
    if (thread_id.IsValid()) {
      DCHECK_NE(thread_manager_->mutex_owner_.load(std::memory_order_relaxed),
                thread_id);
      base::MutexGuard lock_guard(&thread_data_table_mutex_);
      PerIsolateThreadData* per_thread = thread_data_table_.Lookup(thread_id);
      if (per_thread) {
        DCHECK(!per_thread->thread_state_);
        thread_data_table_.Remove(per_thread);
      }
    }
  }
  
  Isolate::PerIsolateThreadData* Isolate::FindPerThreadDataForThisThread() {
    ThreadId thread_id = ThreadId::Current();
    return FindPerThreadDataForThread(thread_id);
  }
  
  Isolate::PerIsolateThreadData* Isolate::FindPerThreadDataForThread(
      ThreadId thread_id) {
    PerIsolateThreadData* per_thread = nullptr;
    {
      base::MutexGuard lock_guard(&thread_data_table_mutex_);
      per_thread = thread_data_table_.Lookup(thread_id);
    }
    return per_thread;
  }
  
  void Isolate::InitializeOncePerProcess() {
    isolate_key_ = base::Thread::CreateThreadLocalKey();
  #if DEBUG
    bool expected = false;
    DCHECK_EQ(true, isolate_key_created_.compare_exchange_strong(
                        expected, true, std::memory_order_relaxed));
  #endif
    per_isolate_thread_data_key_ = base::Thread::CreateThreadLocalKey();
  }
  
  Address Isolate::get_address_from_id(IsolateAddressId id) {
    return isolate_addresses_[id];
  }
  
  char* Isolate::Iterate(RootVisitor* v, char* thread_storage) {
    ThreadLocalTop* thread = reinterpret_cast<ThreadLocalTop*>(thread_storage);
    Iterate(v, thread);
    return thread_storage + sizeof(ThreadLocalTop);
  }
  
  void Isolate::IterateThread(ThreadVisitor* v, char* t) {
    ThreadLocalTop* thread = reinterpret_cast<ThreadLocalTop*>(t);
    v->VisitThread(this, thread);
  }
  
  void Isolate::Iterate(RootVisitor* v, ThreadLocalTop* thread) {
    // Visit the roots from the top for a given thread.
    v->VisitRootPointer(Root::kStackRoots, nullptr,
                        FullObjectSlot(&thread->pending_exception_));
    v->VisitRootPointer(Root::kStackRoots, nullptr,
                        FullObjectSlot(&thread->pending_message_obj_));
    v->VisitRootPointer(Root::kStackRoots, nullptr,
                        FullObjectSlot(&thread->context_));
    v->VisitRootPointer(Root::kStackRoots, nullptr,
                        FullObjectSlot(&thread->scheduled_exception_));
  
    for (v8::TryCatch* block = thread->try_catch_handler_; block != nullptr;
         block = block->next_) {
      // TODO(3770): Make TryCatch::exception_ an Address (and message_obj_ too).
      v->VisitRootPointer(
          Root::kStackRoots, nullptr,
          FullObjectSlot(reinterpret_cast<Address>(&(block->exception_))));
      v->VisitRootPointer(
          Root::kStackRoots, nullptr,
          FullObjectSlot(reinterpret_cast<Address>(&(block->message_obj_))));
    }
  
  #ifdef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
    ConservativeStackVisitor stack_visitor(this, v);
    thread_local_top()->stack_.IteratePointers(&stack_visitor);
  #endif
  
    // Iterate over pointers on native execution stack.
  #if V8_ENABLE_WEBASSEMBLY
    wasm::WasmCodeRefScope wasm_code_ref_scope;
  #endif  // V8_ENABLE_WEBASSEMBLY
    for (StackFrameIterator it(this, thread); !it.done(); it.Advance()) {
      it.frame()->Iterate(v);
    }
  }
  
  void Isolate::Iterate(RootVisitor* v) {
    ThreadLocalTop* current_t = thread_local_top();
    Iterate(v, current_t);
  }
  
  void Isolate::RegisterTryCatchHandler(v8::TryCatch* that) {
    thread_local_top()->try_catch_handler_ = that;
  }
  
  void Isolate::UnregisterTryCatchHandler(v8::TryCatch* that) {
    DCHECK(thread_local_top()->try_catch_handler_ == that);
    thread_local_top()->try_catch_handler_ = that->next_;
  }
  
  Handle<String> Isolate::StackTraceString() {
    if (stack_trace_nesting_level_ == 0) {
      stack_trace_nesting_level_++;
      HeapStringAllocator allocator;
      StringStream::ClearMentionedObjectCache(this);
      StringStream accumulator(&allocator);
      incomplete_message_ = &accumulator;
      PrintStack(&accumulator);
      Handle<String> stack_trace = accumulator.ToString(this);
      incomplete_message_ = nullptr;
      stack_trace_nesting_level_ = 0;
      return stack_trace;
    } else if (stack_trace_nesting_level_ == 1) {
      stack_trace_nesting_level_++;
      base::OS::PrintError(
          "\n\nAttempt to print stack while printing stack (double fault)\n");
      base::OS::PrintError(
          "If you are lucky you may find a partial stack dump on stdout.\n\n");
      incomplete_message_->OutputToStdOut();
      return factory()->empty_string();
    } else {
      base::OS::Abort();
      // Unreachable
      return factory()->empty_string();
    }
  }
  
  void Isolate::PushStackTraceAndDie(void* ptr1, void* ptr2, void* ptr3,
                                     void* ptr4) {
    StackTraceFailureMessage message(this, ptr1, ptr2, ptr3, ptr4);
    message.Print();
    base::OS::Abort();
  }
  
  void StackTraceFailureMessage::Print() volatile {
    // Print the details of this failure message object, including its own address
    // to force stack allocation.
    base::OS::PrintError(
        "Stacktrace:\n   ptr1=%p\n    ptr2=%p\n    ptr3=%p\n    ptr4=%p\n    "
        "failure_message_object=%p\n%s",
        ptr1_, ptr2_, ptr3_, ptr4_, this, &js_stack_trace_[0]);
  }
  
  StackTraceFailureMessage::StackTraceFailureMessage(Isolate* isolate, void* ptr1,
                                                     void* ptr2, void* ptr3,
                                                     void* ptr4) {
    isolate_ = isolate;
    ptr1_ = ptr1;
    ptr2_ = ptr2;
    ptr3_ = ptr3;
    ptr4_ = ptr4;
    // Write a stracktrace into the {js_stack_trace_} buffer.
    const size_t buffer_length = arraysize(js_stack_trace_);
    memset(&js_stack_trace_, 0, buffer_length);
    FixedStringAllocator fixed(&js_stack_trace_[0], buffer_length - 1);
    StringStream accumulator(&fixed, StringStream::kPrintObjectConcise);
    isolate->PrintStack(&accumulator, Isolate::kPrintStackVerbose);
    // Keeping a reference to the last code objects to increase likelyhood that
    // they get included in the minidump.
    const size_t code_objects_length = arraysize(code_objects_);
    size_t i = 0;
    StackFrameIterator it(isolate);
    for (; !it.done() && i < code_objects_length; it.Advance()) {
      code_objects_[i++] =
          reinterpret_cast<void*>(it.frame()->unchecked_code().ptr());
    }
  }
  
  class StackTraceBuilder {
   public:
    enum FrameFilterMode { ALL, CURRENT_SECURITY_CONTEXT };
  
    StackTraceBuilder(Isolate* isolate, FrameSkipMode mode, int limit,
                      Handle<Object> caller, FrameFilterMode filter_mode)
        : isolate_(isolate),
          mode_(mode),
          limit_(limit),
          caller_(caller),
          skip_next_frame_(mode != SKIP_NONE),
          check_security_context_(filter_mode == CURRENT_SECURITY_CONTEXT) {
      DCHECK_IMPLIES(mode_ == SKIP_UNTIL_SEEN, caller_->IsJSFunction());
      // Modern web applications are usually built with multiple layers of
      // framework and library code, and stack depth tends to be more than
      // a dozen frames, so we over-allocate a bit here to avoid growing
      // the elements array in the common case.
      elements_ = isolate->factory()->NewFixedArray(std::min(64, limit));
    }
  
    void AppendAsyncFrame(Handle<JSGeneratorObject> generator_object) {
      Handle<JSFunction> function(generator_object->function(), isolate_);
      if (!IsVisibleInStackTrace(function)) return;
      int flags = StackFrameInfo::kIsAsync;
      if (IsStrictFrame(function)) flags |= StackFrameInfo::kIsStrict;
  
      Handle<Object> receiver(generator_object->receiver(), isolate_);
      Handle<BytecodeArray> code(function->shared().GetBytecodeArray(isolate_),
                                 isolate_);
      // The stored bytecode offset is relative to a different base than what
      // is used in the source position table, hence the subtraction.
      int offset = Smi::ToInt(generator_object->input_or_debug_pos()) -
                   (BytecodeArray::kHeaderSize - kHeapObjectTag);
  
      Handle<FixedArray> parameters = isolate_->factory()->empty_fixed_array();
      if (V8_UNLIKELY(FLAG_detailed_error_stack_trace)) {
        parameters = isolate_->factory()->CopyFixedArrayUpTo(
            handle(generator_object->parameters_and_registers(), isolate_),
            function->shared().internal_formal_parameter_count());
      }
  
      AppendFrame(receiver, function, code, offset, flags, parameters);
    }
  
    void AppendPromiseCombinatorFrame(Handle<JSFunction> element_function,
                                      Handle<JSFunction> combinator) {
      if (!IsVisibleInStackTrace(combinator)) return;
      int flags =
          StackFrameInfo::kIsAsync | StackFrameInfo::kIsSourcePositionComputed;
  
      Handle<Object> receiver(combinator->native_context().promise_function(),
                              isolate_);
      Handle<Code> code(combinator->code(), isolate_);
  
      // TODO(mmarchini) save Promises list from the Promise combinator
      Handle<FixedArray> parameters = isolate_->factory()->empty_fixed_array();
  
      // We store the offset of the promise into the element function's
      // hash field for element callbacks.
      int promise_index =
          Smi::ToInt(Smi::cast(element_function->GetIdentityHash())) - 1;
  
      AppendFrame(receiver, combinator, code, promise_index, flags, parameters);
    }
  
    void AppendJavaScriptFrame(
        FrameSummary::JavaScriptFrameSummary const& summary) {
      // Filter out internal frames that we do not want to show.
      if (!IsVisibleInStackTrace(summary.function())) return;
  
      int flags = 0;
      Handle<JSFunction> function = summary.function();
      if (IsStrictFrame(function)) flags |= StackFrameInfo::kIsStrict;
      if (summary.is_constructor()) flags |= StackFrameInfo::kIsConstructor;
  
      AppendFrame(summary.receiver(), function, summary.abstract_code(),
                  summary.code_offset(), flags, summary.parameters());
    }
  
  #if V8_ENABLE_WEBASSEMBLY
    void AppendWasmFrame(FrameSummary::WasmFrameSummary const& summary) {
      if (summary.code()->kind() != wasm::WasmCode::kFunction) return;
      Handle<WasmInstanceObject> instance = summary.wasm_instance();
      int flags = StackFrameInfo::kIsWasm;
      if (instance->module_object().is_asm_js()) {
        flags |= StackFrameInfo::kIsAsmJsWasm;
        if (summary.at_to_number_conversion()) {
          flags |= StackFrameInfo::kIsAsmJsAtNumberConversion;
        }
      }
  
      auto code = Managed<wasm::GlobalWasmCodeRef>::Allocate(
          isolate_, 0, summary.code(),
          instance->module_object().shared_native_module());
      AppendFrame(instance,
                  handle(Smi::FromInt(summary.function_index()), isolate_), code,
                  summary.code_offset(), flags,
                  isolate_->factory()->empty_fixed_array());
    }
  #endif  // V8_ENABLE_WEBASSEMBLY
  
    void AppendBuiltinExitFrame(BuiltinExitFrame* exit_frame) {
      Handle<JSFunction> function(exit_frame->function(), isolate_);
      if (!IsVisibleInStackTrace(function)) return;
  
      // TODO(szuend): Remove this check once the flag is enabled
      //               by default.
      if (!FLAG_experimental_stack_trace_frames &&
          function->shared().IsApiFunction()) {
        return;
      }
  
      Handle<Object> receiver(exit_frame->receiver(), isolate_);
      Handle<Code> code(exit_frame->LookupCode(), isolate_);
      const int offset =
          code->GetOffsetFromInstructionStart(isolate_, exit_frame->pc());
  
      int flags = 0;
      if (IsStrictFrame(function)) flags |= StackFrameInfo::kIsStrict;
      if (exit_frame->IsConstructor()) flags |= StackFrameInfo::kIsConstructor;
  
      Handle<FixedArray> parameters = isolate_->factory()->empty_fixed_array();
      if (V8_UNLIKELY(FLAG_detailed_error_stack_trace)) {
        int param_count = exit_frame->ComputeParametersCount();
        parameters = isolate_->factory()->NewFixedArray(param_count);
        for (int i = 0; i < param_count; i++) {
          parameters->set(i, exit_frame->GetParameter(i));
        }
      }
  
      AppendFrame(receiver, function, code, offset, flags, parameters);
    }
  
    bool Full() { return index_ >= limit_; }
  
    Handle<FixedArray> Build() {
      return FixedArray::ShrinkOrEmpty(isolate_, elements_, index_);
    }
  
   private:
    // Poison stack frames below the first strict mode frame.
    // The stack trace API should not expose receivers and function
    // objects on frames deeper than the top-most one with a strict mode
    // function.
    bool IsStrictFrame(Handle<JSFunction> function) {
      if (!encountered_strict_function_) {
        encountered_strict_function_ =
            is_strict(function->shared().language_mode());
      }
      return encountered_strict_function_;
    }
  
    // Determines whether the given stack frame should be displayed in a stack
    // trace.
    bool IsVisibleInStackTrace(Handle<JSFunction> function) {
      return ShouldIncludeFrame(function) && IsNotHidden(function) &&
             IsInSameSecurityContext(function);
    }
  
    // This mechanism excludes a number of uninteresting frames from the stack
    // trace. This can be be the first frame (which will be a builtin-exit frame
    // for the error constructor builtin) or every frame until encountering a
    // user-specified function.
    bool ShouldIncludeFrame(Handle<JSFunction> function) {
      switch (mode_) {
        case SKIP_NONE:
          return true;
        case SKIP_FIRST:
          if (!skip_next_frame_) return true;
          skip_next_frame_ = false;
          return false;
        case SKIP_UNTIL_SEEN:
          if (skip_next_frame_ && (*function == *caller_)) {
            skip_next_frame_ = false;
            return false;
          }
          return !skip_next_frame_;
      }
      UNREACHABLE();
    }
  
    bool IsNotHidden(Handle<JSFunction> function) {
      // Functions defined not in user scripts are not visible unless directly
      // exposed, in which case the native flag is set.
      // The --builtins-in-stack-traces command line flag allows including
      // internal call sites in the stack trace for debugging purposes.
      if (!FLAG_builtins_in_stack_traces &&
          !function->shared().IsUserJavaScript()) {
        return function->shared().native() || function->shared().IsApiFunction();
      }
      return true;
    }
  
    bool IsInSameSecurityContext(Handle<JSFunction> function) {
      if (!check_security_context_) return true;
      return isolate_->context().HasSameSecurityTokenAs(function->context());
    }
  
    void AppendFrame(Handle<Object> receiver_or_instance, Handle<Object> function,
                     Handle<HeapObject> code, int offset, int flags,
                     Handle<FixedArray> parameters) {
      DCHECK_LE(index_, elements_->length());
      DCHECK_LE(elements_->length(), limit_);
      if (index_ == elements_->length()) {
        elements_ = isolate_->factory()->CopyFixedArrayAndGrow(
            elements_, std::min(16, limit_ - elements_->length()));
      }
      if (receiver_or_instance->IsTheHole(isolate_)) {
        // TODO(jgruber): Fix all cases in which frames give us a hole value
        // (e.g. the receiver in RegExp constructor frames).
        receiver_or_instance = isolate_->factory()->undefined_value();
      }
      auto info = isolate_->factory()->NewStackFrameInfo(
          receiver_or_instance, function, code, offset, flags, parameters);
      elements_->set(index_++, *info);
    }
  
    Isolate* isolate_;
    const FrameSkipMode mode_;
    int index_ = 0;
    const int limit_;
    const Handle<Object> caller_;
    bool skip_next_frame_;
    bool encountered_strict_function_ = false;
    const bool check_security_context_;
    Handle<FixedArray> elements_;
  };
  
  bool GetStackTraceLimit(Isolate* isolate, int* result) {
    Handle<JSObject> error = isolate->error_function();
  
    Handle<String> key = isolate->factory()->stackTraceLimit_string();
    Handle<Object> stack_trace_limit = JSReceiver::GetDataProperty(error, key);
    if (!stack_trace_limit->IsNumber()) return false;
  
    // Ensure that limit is not negative.
    *result = std::max(FastD2IChecked(stack_trace_limit->Number()), 0);
  
    if (*result != FLAG_stack_trace_limit) {
      isolate->CountUsage(v8::Isolate::kErrorStackTraceLimit);
    }
  
    return true;
  }
  
  bool NoExtension(const v8::FunctionCallbackInfo<v8::Value>&) { return false; }
  
  namespace {
  
  bool IsBuiltinFunction(Isolate* isolate, HeapObject object,
                         Builtins::Name builtin_index) {
    if (!object.IsJSFunction()) return false;
    JSFunction const function = JSFunction::cast(object);
    return function.code() == isolate->builtins()->builtin(builtin_index);
  }
  
  void CaptureAsyncStackTrace(Isolate* isolate, Handle<JSPromise> promise,
                              StackTraceBuilder* builder) {
    while (!builder->Full()) {
      // Check that the {promise} is not settled.
      if (promise->status() != Promise::kPending) return;
  
      // Check that we have exactly one PromiseReaction on the {promise}.
      if (!promise->reactions().IsPromiseReaction()) return;
      Handle<PromiseReaction> reaction(
          PromiseReaction::cast(promise->reactions()), isolate);
      if (!reaction->next().IsSmi()) return;
  
      // Check if the {reaction} has one of the known async function or
      // async generator continuations as its fulfill handler.
      if (IsBuiltinFunction(isolate, reaction->fulfill_handler(),
                            Builtins::kAsyncFunctionAwaitResolveClosure) ||
          IsBuiltinFunction(isolate, reaction->fulfill_handler(),
                            Builtins::kAsyncGeneratorAwaitResolveClosure) ||
          IsBuiltinFunction(isolate, reaction->fulfill_handler(),
                            Builtins::kAsyncGeneratorYieldResolveClosure)) {
        // Now peak into the handlers' AwaitContext to get to
        // the JSGeneratorObject for the async function.
        Handle<Context> context(
            JSFunction::cast(reaction->fulfill_handler()).context(), isolate);
        Handle<JSGeneratorObject> generator_object(
            JSGeneratorObject::cast(context->extension()), isolate);
        CHECK(generator_object->is_suspended());
  
        // Append async frame corresponding to the {generator_object}.
        builder->AppendAsyncFrame(generator_object);
  
        // Try to continue from here.
        if (generator_object->IsJSAsyncFunctionObject()) {
          Handle<JSAsyncFunctionObject> async_function_object =
              Handle<JSAsyncFunctionObject>::cast(generator_object);
          promise = handle(async_function_object->promise(), isolate);
        } else {
          Handle<JSAsyncGeneratorObject> async_generator_object =
              Handle<JSAsyncGeneratorObject>::cast(generator_object);
          if (async_generator_object->queue().IsUndefined(isolate)) return;
          Handle<AsyncGeneratorRequest> async_generator_request(
              AsyncGeneratorRequest::cast(async_generator_object->queue()),
              isolate);
          promise = handle(JSPromise::cast(async_generator_request->promise()),
                           isolate);
        }
      } else if (IsBuiltinFunction(isolate, reaction->fulfill_handler(),
                                   Builtins::kPromiseAllResolveElementClosure)) {
        Handle<JSFunction> function(JSFunction::cast(reaction->fulfill_handler()),
                                    isolate);
        Handle<Context> context(function->context(), isolate);
        Handle<JSFunction> combinator(context->native_context().promise_all(),
                                      isolate);
        builder->AppendPromiseCombinatorFrame(function, combinator);
  
        // Now peak into the Promise.all() resolve element context to
        // find the promise capability that's being resolved when all
        // the concurrent promises resolve.
        int const index =
            PromiseBuiltins::kPromiseAllResolveElementCapabilitySlot;
        Handle<PromiseCapability> capability(
            PromiseCapability::cast(context->get(index)), isolate);
        if (!capability->promise().IsJSPromise()) return;
        promise = handle(JSPromise::cast(capability->promise()), isolate);
      } else if (IsBuiltinFunction(isolate, reaction->reject_handler(),
                                   Builtins::kPromiseAnyRejectElementClosure)) {
        Handle<JSFunction> function(JSFunction::cast(reaction->reject_handler()),
                                    isolate);
        Handle<Context> context(function->context(), isolate);
        Handle<JSFunction> combinator(context->native_context().promise_any(),
                                      isolate);
        builder->AppendPromiseCombinatorFrame(function, combinator);
  
        // Now peak into the Promise.any() reject element context to
        // find the promise capability that's being resolved when any of
        // the concurrent promises resolve.
        int const index = PromiseBuiltins::kPromiseAnyRejectElementCapabilitySlot;
        Handle<PromiseCapability> capability(
            PromiseCapability::cast(context->get(index)), isolate);
        if (!capability->promise().IsJSPromise()) return;
        promise = handle(JSPromise::cast(capability->promise()), isolate);
      } else if (IsBuiltinFunction(isolate, reaction->fulfill_handler(),
                                   Builtins::kPromiseCapabilityDefaultResolve)) {
        Handle<JSFunction> function(JSFunction::cast(reaction->fulfill_handler()),
                                    isolate);
        Handle<Context> context(function->context(), isolate);
        promise =
            handle(JSPromise::cast(context->get(PromiseBuiltins::kPromiseSlot)),
                   isolate);
      } else {
        // We have some generic promise chain here, so try to
        // continue with the chained promise on the reaction
        // (only works for native promise chains).
        Handle<HeapObject> promise_or_capability(
            reaction->promise_or_capability(), isolate);
        if (promise_or_capability->IsJSPromise()) {
          promise = Handle<JSPromise>::cast(promise_or_capability);
        } else if (promise_or_capability->IsPromiseCapability()) {
          Handle<PromiseCapability> capability =
              Handle<PromiseCapability>::cast(promise_or_capability);
          if (!capability->promise().IsJSPromise()) return;
          promise = handle(JSPromise::cast(capability->promise()), isolate);
        } else {
          // Otherwise the {promise_or_capability} must be undefined here.
          CHECK(promise_or_capability->IsUndefined(isolate));
          return;
        }
      }
    }
  }
  
  struct CaptureStackTraceOptions {
    int limit;
    // 'filter_mode' and 'skip_mode' are somewhat orthogonal. 'filter_mode'
    // specifies whether to capture all frames, or just frames in the same
    // security context. While 'skip_mode' allows skipping the first frame.
    FrameSkipMode skip_mode;
    StackTraceBuilder::FrameFilterMode filter_mode;
  
    bool capture_builtin_exit_frames;
    bool capture_only_frames_subject_to_debugging;
    bool async_stack_trace;
  };
  
  Handle<FixedArray> CaptureStackTrace(Isolate* isolate, Handle<Object> caller,
                                       CaptureStackTraceOptions options) {
    DisallowJavascriptExecution no_js(isolate);
  
    TRACE_EVENT_BEGIN1(TRACE_DISABLED_BY_DEFAULT("v8.stack_trace"),
                       "CaptureStackTrace", "maxFrameCount", options.limit);
  
  #if V8_ENABLE_WEBASSEMBLY
    wasm::WasmCodeRefScope code_ref_scope;
  #endif  // V8_ENABLE_WEBASSEMBLY
  
    StackTraceBuilder builder(isolate, options.skip_mode, options.limit, caller,
                              options.filter_mode);
  
    // Build the regular stack trace, and remember the last relevant
    // frame ID and inlined index (for the async stack trace handling
    // below, which starts from this last frame).
    for (StackFrameIterator it(isolate); !it.done() && !builder.Full();
         it.Advance()) {
      StackFrame* const frame = it.frame();
      switch (frame->type()) {
        case StackFrame::JAVA_SCRIPT_BUILTIN_CONTINUATION:
        case StackFrame::JAVA_SCRIPT_BUILTIN_CONTINUATION_WITH_CATCH:
        case StackFrame::OPTIMIZED:
        case StackFrame::INTERPRETED:
        case StackFrame::BASELINE:
        case StackFrame::BUILTIN:
  #if V8_ENABLE_WEBASSEMBLY
        case StackFrame::WASM:
  #endif  // V8_ENABLE_WEBASSEMBLY
        {
          // A standard frame may include many summarized frames (due to
          // inlining).
          std::vector<FrameSummary> frames;
          CommonFrame::cast(frame)->Summarize(&frames);
          for (size_t i = frames.size(); i-- != 0 && !builder.Full();) {
            auto& summary = frames[i];
            if (options.capture_only_frames_subject_to_debugging &&
                !summary.is_subject_to_debugging()) {
              continue;
            }
  
            if (summary.IsJavaScript()) {
              //=========================================================
              // Handle a JavaScript frame.
              //=========================================================
              auto const& java_script = summary.AsJavaScript();
              builder.AppendJavaScriptFrame(java_script);
  #if V8_ENABLE_WEBASSEMBLY
            } else if (summary.IsWasm()) {
              //=========================================================
              // Handle a Wasm frame.
              //=========================================================
              auto const& wasm = summary.AsWasm();
              builder.AppendWasmFrame(wasm);
  #endif  // V8_ENABLE_WEBASSEMBLY
            }
          }
          break;
        }
  
        case StackFrame::BUILTIN_EXIT:
          if (!options.capture_builtin_exit_frames) continue;
  
          // BuiltinExitFrames are not standard frames, so they do not have
          // Summarize(). However, they may have one JS frame worth showing.
          builder.AppendBuiltinExitFrame(BuiltinExitFrame::cast(frame));
          break;
  
        default:
          break;
      }
    }
  
    // If --async-stack-traces are enabled and the "current microtask" is a
    // PromiseReactionJobTask, we try to enrich the stack trace with async
    // frames.
    if (options.async_stack_trace) {
      Handle<Object> current_microtask = isolate->factory()->current_microtask();
      if (current_microtask->IsPromiseReactionJobTask()) {
        Handle<PromiseReactionJobTask> promise_reaction_job_task =
            Handle<PromiseReactionJobTask>::cast(current_microtask);
        // Check if the {reaction} has one of the known async function or
        // async generator continuations as its fulfill handler.
        if (IsBuiltinFunction(isolate, promise_reaction_job_task->handler(),
                              Builtins::kAsyncFunctionAwaitResolveClosure) ||
            IsBuiltinFunction(isolate, promise_reaction_job_task->handler(),
                              Builtins::kAsyncGeneratorAwaitResolveClosure) ||
            IsBuiltinFunction(isolate, promise_reaction_job_task->handler(),
                              Builtins::kAsyncGeneratorYieldResolveClosure) ||
            IsBuiltinFunction(isolate, promise_reaction_job_task->handler(),
                              Builtins::kAsyncFunctionAwaitRejectClosure) ||
            IsBuiltinFunction(isolate, promise_reaction_job_task->handler(),
                              Builtins::kAsyncGeneratorAwaitRejectClosure)) {
          // Now peak into the handlers' AwaitContext to get to
          // the JSGeneratorObject for the async function.
          Handle<Context> context(
              JSFunction::cast(promise_reaction_job_task->handler()).context(),
              isolate);
          Handle<JSGeneratorObject> generator_object(
              JSGeneratorObject::cast(context->extension()), isolate);
          if (generator_object->is_executing()) {
            if (generator_object->IsJSAsyncFunctionObject()) {
              Handle<JSAsyncFunctionObject> async_function_object =
                  Handle<JSAsyncFunctionObject>::cast(generator_object);
              Handle<JSPromise> promise(async_function_object->promise(),
                                        isolate);
              CaptureAsyncStackTrace(isolate, promise, &builder);
            } else {
              Handle<JSAsyncGeneratorObject> async_generator_object =
                  Handle<JSAsyncGeneratorObject>::cast(generator_object);
              Handle<Object> queue(async_generator_object->queue(), isolate);
              if (!queue->IsUndefined(isolate)) {
                Handle<AsyncGeneratorRequest> async_generator_request =
                    Handle<AsyncGeneratorRequest>::cast(queue);
                Handle<JSPromise> promise(
                    JSPromise::cast(async_generator_request->promise()), isolate);
                CaptureAsyncStackTrace(isolate, promise, &builder);
              }
            }
          }
        } else {
          // The {promise_reaction_job_task} doesn't belong to an await (or
          // yield inside an async generator), but we might still be able to
          // find an async frame if we follow along the chain of promises on
          // the {promise_reaction_job_task}.
          Handle<HeapObject> promise_or_capability(
              promise_reaction_job_task->promise_or_capability(), isolate);
          if (promise_or_capability->IsJSPromise()) {
            Handle<JSPromise> promise =
                Handle<JSPromise>::cast(promise_or_capability);
            CaptureAsyncStackTrace(isolate, promise, &builder);
          }
        }
      }
    }
  
    Handle<FixedArray> stack_trace = builder.Build();
    TRACE_EVENT_END1(TRACE_DISABLED_BY_DEFAULT("v8.stack_trace"),
                     "CaptureStackTrace", "frameCount", stack_trace->length());
    return stack_trace;
  }
  
  }  // namespace
  
  Handle<Object> Isolate::CaptureSimpleStackTrace(Handle<JSReceiver> error_object,
                                                  FrameSkipMode mode,
                                                  Handle<Object> caller) {
    int limit;
    if (!GetStackTraceLimit(this, &limit)) return factory()->undefined_value();
  
    CaptureStackTraceOptions options;
    options.limit = limit;
    options.skip_mode = mode;
    options.capture_builtin_exit_frames = true;
    options.async_stack_trace = FLAG_async_stack_traces;
    options.filter_mode = StackTraceBuilder::CURRENT_SECURITY_CONTEXT;
    options.capture_only_frames_subject_to_debugging = false;
  
    return CaptureStackTrace(this, caller, options);
  }
  
  MaybeHandle<JSReceiver> Isolate::CaptureAndSetDetailedStackTrace(
      Handle<JSReceiver> error_object) {
    if (capture_stack_trace_for_uncaught_exceptions_) {
      // Capture stack trace for a detailed exception message.
      Handle<Name> key = factory()->detailed_stack_trace_symbol();
      Handle<FixedArray> stack_trace = CaptureCurrentStackTrace(
          stack_trace_for_uncaught_exceptions_frame_limit_,
          stack_trace_for_uncaught_exceptions_options_);
      RETURN_ON_EXCEPTION(
          this,
          Object::SetProperty(this, error_object, key, stack_trace,
                              StoreOrigin::kMaybeKeyed,
                              Just(ShouldThrow::kThrowOnError)),
          JSReceiver);
    }
    return error_object;
  }
  
  MaybeHandle<JSReceiver> Isolate::CaptureAndSetSimpleStackTrace(
      Handle<JSReceiver> error_object, FrameSkipMode mode,
      Handle<Object> caller) {
    // Capture stack trace for simple stack trace string formatting.
    Handle<Name> key = factory()->stack_trace_symbol();
    Handle<Object> stack_trace =
        CaptureSimpleStackTrace(error_object, mode, caller);
    RETURN_ON_EXCEPTION(this,
                        Object::SetProperty(this, error_object, key, stack_trace,
                                            StoreOrigin::kMaybeKeyed,
                                            Just(ShouldThrow::kThrowOnError)),
                        JSReceiver);
    return error_object;
  }
  
  Handle<FixedArray> Isolate::GetDetailedStackTrace(
      Handle<JSObject> error_object) {
    Handle<Name> key_detailed = factory()->detailed_stack_trace_symbol();
    Handle<Object> stack_trace =
        JSReceiver::GetDataProperty(error_object, key_detailed);
    if (stack_trace->IsFixedArray()) return Handle<FixedArray>::cast(stack_trace);
    return Handle<FixedArray>();
  }
  
  Address Isolate::GetAbstractPC(int* line, int* column) {
    JavaScriptFrameIterator it(this);
  
    if (it.done()) {
      *line = -1;
      *column = -1;
      return kNullAddress;
    }
    JavaScriptFrame* frame = it.frame();
    DCHECK(!frame->is_builtin());
  
    Handle<SharedFunctionInfo> shared = handle(frame->function().shared(), this);
    SharedFunctionInfo::EnsureSourcePositionsAvailable(this, shared);
    int position = frame->position();
  
    Object maybe_script = frame->function().shared().script();
    if (maybe_script.IsScript()) {
      Handle<Script> script(Script::cast(maybe_script), this);
      Script::PositionInfo info;
      Script::GetPositionInfo(script, position, &info, Script::WITH_OFFSET);
      *line = info.line + 1;
      *column = info.column + 1;
    } else {
      *line = position;
      *column = -1;
    }
  
    if (frame->is_unoptimized()) {
      UnoptimizedFrame* iframe = static_cast<UnoptimizedFrame*>(frame);
      Address bytecode_start =
          iframe->GetBytecodeArray().GetFirstBytecodeAddress();
      return bytecode_start + iframe->GetBytecodeOffset();
    }
  
    return frame->pc();
  }
  
  Handle<FixedArray> Isolate::CaptureCurrentStackTrace(
      int frame_limit, StackTrace::StackTraceOptions stack_trace_options) {
    CaptureStackTraceOptions options;
    options.limit = std::max(frame_limit, 0);  // Ensure no negative values.
    options.skip_mode = SKIP_NONE;
    options.capture_builtin_exit_frames = false;
    options.async_stack_trace = false;
    options.filter_mode =
        (stack_trace_options & StackTrace::kExposeFramesAcrossSecurityOrigins)
            ? StackTraceBuilder::ALL
            : StackTraceBuilder::CURRENT_SECURITY_CONTEXT;
    options.capture_only_frames_subject_to_debugging = true;
  
    return CaptureStackTrace(this, factory()->undefined_value(), options);
  }
  
  void Isolate::PrintStack(FILE* out, PrintStackMode mode) {
    if (stack_trace_nesting_level_ == 0) {
      stack_trace_nesting_level_++;
      StringStream::ClearMentionedObjectCache(this);
      HeapStringAllocator allocator;
      StringStream accumulator(&allocator);
      incomplete_message_ = &accumulator;
      PrintStack(&accumulator, mode);
      accumulator.OutputToFile(out);
      InitializeLoggingAndCounters();
      accumulator.Log(this);
      incomplete_message_ = nullptr;
      stack_trace_nesting_level_ = 0;
    } else if (stack_trace_nesting_level_ == 1) {
      stack_trace_nesting_level_++;
      base::OS::PrintError(
          "\n\nAttempt to print stack while printing stack (double fault)\n");
      base::OS::PrintError(
          "If you are lucky you may find a partial stack dump on stdout.\n\n");
      incomplete_message_->OutputToFile(out);
    }
  }
  
  static void PrintFrames(Isolate* isolate, StringStream* accumulator,
                          StackFrame::PrintMode mode) {
    StackFrameIterator it(isolate);
    for (int i = 0; !it.done(); it.Advance()) {
      it.frame()->Print(accumulator, mode, i++);
    }
  }
  
  void Isolate::PrintStack(StringStream* accumulator, PrintStackMode mode) {
    HandleScope scope(this);
    DCHECK(accumulator->IsMentionedObjectCacheClear(this));
  
    // Avoid printing anything if there are no frames.
    if (c_entry_fp(thread_local_top()) == 0) return;
  
    accumulator->Add(
        "\n==== JS stack trace =========================================\n\n");
    PrintFrames(this, accumulator, StackFrame::OVERVIEW);
    if (mode == kPrintStackVerbose) {
      accumulator->Add(
          "\n==== Details ================================================\n\n");
      PrintFrames(this, accumulator, StackFrame::DETAILS);
      accumulator->PrintMentionedObjectCache(this);
    }
    accumulator->Add("=====================\n\n");
  }
  
  void Isolate::SetFailedAccessCheckCallback(
      v8::FailedAccessCheckCallback callback) {
    thread_local_top()->failed_access_check_callback_ = callback;
  }
  
  void Isolate::ReportFailedAccessCheck(Handle<JSObject> receiver) {
    if (!thread_local_top()->failed_access_check_callback_) {
      return ScheduleThrow(*factory()->NewTypeError(MessageTemplate::kNoAccess));
    }
  
    DCHECK(receiver->IsAccessCheckNeeded());
    DCHECK(!context().is_null());
  
    // Get the data object from access check info.
    HandleScope scope(this);
    Handle<Object> data;
    {
      DisallowGarbageCollection no_gc;
      AccessCheckInfo access_check_info = AccessCheckInfo::Get(this, receiver);
      if (access_check_info.is_null()) {
        no_gc.Release();
        return ScheduleThrow(
            *factory()->NewTypeError(MessageTemplate::kNoAccess));
      }
      data = handle(access_check_info.data(), this);
    }
  
    // Leaving JavaScript.
    VMState<EXTERNAL> state(this);
    thread_local_top()->failed_access_check_callback_(
        v8::Utils::ToLocal(receiver), v8::ACCESS_HAS, v8::Utils::ToLocal(data));
  }
  
  bool Isolate::MayAccess(Handle<Context> accessing_context,
                          Handle<JSObject> receiver) {
    DCHECK(receiver->IsJSGlobalProxy() || receiver->IsAccessCheckNeeded());
  
    // Check for compatibility between the security tokens in the
    // current lexical context and the accessed object.
  
    // During bootstrapping, callback functions are not enabled yet.
    if (bootstrapper()->IsActive()) return true;
    {
      DisallowGarbageCollection no_gc;
  
      if (receiver->IsJSGlobalProxy()) {
        Object receiver_context = JSGlobalProxy::cast(*receiver).native_context();
        if (!receiver_context.IsContext()) return false;
  
        // Get the native context of current top context.
        // avoid using Isolate::native_context() because it uses Handle.
        Context native_context =
            accessing_context->global_object().native_context();
        if (receiver_context == native_context) return true;
  
        if (Context::cast(receiver_context).security_token() ==
            native_context.security_token())
          return true;
      }
    }
  
    HandleScope scope(this);
    Handle<Object> data;
    v8::AccessCheckCallback callback = nullptr;
    {
      DisallowGarbageCollection no_gc;
      AccessCheckInfo access_check_info = AccessCheckInfo::Get(this, receiver);
      if (access_check_info.is_null()) return false;
      Object fun_obj = access_check_info.callback();
      callback = v8::ToCData<v8::AccessCheckCallback>(fun_obj);
      data = handle(access_check_info.data(), this);
    }
  
    LOG(this, ApiSecurityCheck());
  
    {
      // Leaving JavaScript.
      VMState<EXTERNAL> state(this);
      return callback(v8::Utils::ToLocal(accessing_context),
                      v8::Utils::ToLocal(receiver), v8::Utils::ToLocal(data));
    }
  }
  
  Object Isolate::StackOverflow() {
    if (FLAG_correctness_fuzzer_suppressions) {
      FATAL("Aborting on stack overflow");
    }
  
    DisallowJavascriptExecution no_js(this);
    HandleScope scope(this);
  
    Handle<JSFunction> fun = range_error_function();
    Handle<Object> msg = factory()->NewStringFromAsciiChecked(
        MessageFormatter::TemplateString(MessageTemplate::kStackOverflow));
    Handle<Object> options = factory()->undefined_value();
    Handle<Object> no_caller;
    Handle<JSObject> exception;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
        this, exception,
        ErrorUtils::Construct(this, fun, fun, msg, options, SKIP_NONE, no_caller,
                              ErrorUtils::StackTraceCollection::kSimple));
    JSObject::AddProperty(this, exception, factory()->wasm_uncatchable_symbol(),
                          factory()->true_value(), NONE);
  
    Throw(*exception);
  
  #ifdef VERIFY_HEAP
    if (FLAG_verify_heap && FLAG_stress_compaction) {
      heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                GarbageCollectionReason::kTesting);
    }
  #endif  // VERIFY_HEAP
  
    return ReadOnlyRoots(heap()).exception();
  }
  
  Object Isolate::ThrowAt(Handle<JSObject> exception, MessageLocation* location) {
    Handle<Name> key_start_pos = factory()->error_start_pos_symbol();
    Object::SetProperty(this, exception, key_start_pos,
                        handle(Smi::FromInt(location->start_pos()), this),
                        StoreOrigin::kMaybeKeyed,
                        Just(ShouldThrow::kThrowOnError))
        .Check();
  
    Handle<Name> key_end_pos = factory()->error_end_pos_symbol();
    Object::SetProperty(this, exception, key_end_pos,
                        handle(Smi::FromInt(location->end_pos()), this),
                        StoreOrigin::kMaybeKeyed,
                        Just(ShouldThrow::kThrowOnError))
        .Check();
  
    Handle<Name> key_script = factory()->error_script_symbol();
    Object::SetProperty(this, exception, key_script, location->script(),
                        StoreOrigin::kMaybeKeyed,
                        Just(ShouldThrow::kThrowOnError))
        .Check();
  
    return ThrowInternal(*exception, location);
  }
  
  Object Isolate::TerminateExecution() {
    return Throw(ReadOnlyRoots(this).termination_exception());
  }
  
  void Isolate::CancelTerminateExecution() {
    if (try_catch_handler()) {
      try_catch_handler()->has_terminated_ = false;
    }
    if (has_pending_exception() &&
        pending_exception() == ReadOnlyRoots(this).termination_exception()) {
      thread_local_top()->external_caught_exception_ = false;
      clear_pending_exception();
    }
    if (has_scheduled_exception() &&
        scheduled_exception() == ReadOnlyRoots(this).termination_exception()) {
      thread_local_top()->external_caught_exception_ = false;
      clear_scheduled_exception();
    }
  }
  
  void Isolate::RequestInterrupt(InterruptCallback callback, void* data) {
    ExecutionAccess access(this);
    api_interrupts_queue_.push(InterruptEntry(callback, data));
    stack_guard()->RequestApiInterrupt();
  }
  
  void Isolate::InvokeApiInterruptCallbacks() {
    RCS_SCOPE(this, RuntimeCallCounterId::kInvokeApiInterruptCallbacks);
    // Note: callback below should be called outside of execution access lock.
    while (true) {
      InterruptEntry entry;
      {
        ExecutionAccess access(this);
        if (api_interrupts_queue_.empty()) return;
        entry = api_interrupts_queue_.front();
        api_interrupts_queue_.pop();
      }
      VMState<EXTERNAL> state(this);
      HandleScope handle_scope(this);
      entry.first(reinterpret_cast<v8::Isolate*>(this), entry.second);
    }
  }
  
  namespace {
  
  void ReportBootstrappingException(Handle<Object> exception,
                                    MessageLocation* location) {
    base::OS::PrintError("Exception thrown during bootstrapping\n");
    if (location == nullptr || location->script().is_null()) return;
    // We are bootstrapping and caught an error where the location is set
    // and we have a script for the location.
    // In this case we could have an extension (or an internal error
    // somewhere) and we print out the line number at which the error occurred
    // to the console for easier debugging.
    int line_number =
        location->script()->GetLineNumber(location->start_pos()) + 1;
    if (exception->IsString() && location->script()->name().IsString()) {
      base::OS::PrintError(
          "Extension or internal compilation error: %s in %s at line %d.\n",
          String::cast(*exception).ToCString().get(),
          String::cast(location->script()->name()).ToCString().get(),
          line_number);
    } else if (location->script()->name().IsString()) {
      base::OS::PrintError(
          "Extension or internal compilation error in %s at line %d.\n",
          String::cast(location->script()->name()).ToCString().get(),
          line_number);
    } else if (exception->IsString()) {
      base::OS::PrintError("Extension or internal compilation error: %s.\n",
                           String::cast(*exception).ToCString().get());
    } else {
      base::OS::PrintError("Extension or internal compilation error.\n");
    }
  #ifdef OBJECT_PRINT
    // Since comments and empty lines have been stripped from the source of
    // builtins, print the actual source here so that line numbers match.
    if (location->script()->source().IsString()) {
      Handle<String> src(String::cast(location->script()->source()),
                         location->script()->GetIsolate());
      PrintF("Failing script:");
      int len = src->length();
      if (len == 0) {
        PrintF(" <not available>\n");
      } else {
        PrintF("\n");
        int line_number = 1;
        PrintF("%5d: ", line_number);
        for (int i = 0; i < len; i++) {
          uint16_t character = src->Get(i);
          PrintF("%c", character);
          if (character == '\n' && i < len - 2) {
            PrintF("%5d: ", ++line_number);
          }
        }
        PrintF("\n");
      }
    }
  #endif
  }
  
  }  // anonymous namespace
  
  Handle<JSMessageObject> Isolate::CreateMessageOrAbort(
      Handle<Object> exception, MessageLocation* location) {
    Handle<JSMessageObject> message_obj = CreateMessage(exception, location);
  
    // If the abort-on-uncaught-exception flag is specified, and if the
    // embedder didn't specify a custom uncaught exception callback,
    // or if the custom callback determined that V8 should abort, then
    // abort.
    if (FLAG_abort_on_uncaught_exception) {
      CatchType prediction = PredictExceptionCatcher();
      if ((prediction == NOT_CAUGHT || prediction == CAUGHT_BY_EXTERNAL) &&
          (!abort_on_uncaught_exception_callback_ ||
           abort_on_uncaught_exception_callback_(
               reinterpret_cast<v8::Isolate*>(this)))) {
        // Prevent endless recursion.
        FLAG_abort_on_uncaught_exception = false;
        // This flag is intended for use by JavaScript developers, so
        // print a user-friendly stack trace (not an internal one).
        PrintF(stderr, "%s\n\nFROM\n",
               MessageHandler::GetLocalizedMessage(this, message_obj).get());
        PrintCurrentStackTrace(stderr);
        base::OS::Abort();
      }
    }
  
    return message_obj;
  }
  
  Object Isolate::ThrowInternal(Object raw_exception, MessageLocation* location) {
    DCHECK(!has_pending_exception());
    DCHECK_IMPLIES(trap_handler::IsTrapHandlerEnabled(),
                   !trap_handler::IsThreadInWasm());
  
    HandleScope scope(this);
    Handle<Object> exception(raw_exception, this);
  
    if (FLAG_print_all_exceptions) {
      printf("=========================================================\n");
      printf("Exception thrown:\n");
      if (location) {
        Handle<Script> script = location->script();
        Handle<Object> name(script->GetNameOrSourceURL(), this);
        printf("at ");
        if (name->IsString() && String::cast(*name).length() > 0)
          String::cast(*name).PrintOn(stdout);
        else
          printf("<anonymous>");
  // Script::GetLineNumber and Script::GetColumnNumber can allocate on the heap to
  // initialize the line_ends array, so be careful when calling them.
  #ifdef DEBUG
        if (AllowGarbageCollection::IsAllowed()) {
  #else
        if ((false)) {
  #endif
          printf(", %d:%d - %d:%d\n",
                 Script::GetLineNumber(script, location->start_pos()) + 1,
                 Script::GetColumnNumber(script, location->start_pos()),
                 Script::GetLineNumber(script, location->end_pos()) + 1,
                 Script::GetColumnNumber(script, location->end_pos()));
          // Make sure to update the raw exception pointer in case it moved.
          raw_exception = *exception;
        } else {
          printf(", line %d\n", script->GetLineNumber(location->start_pos()) + 1);
        }
      }
      raw_exception.Print();
      printf("Stack Trace:\n");
      PrintStack(stdout);
      printf("=========================================================\n");
    }
  
    // Determine whether a message needs to be created for the given exception
    // depending on the following criteria:
    // 1) External v8::TryCatch missing: Always create a message because any
    //    JavaScript handler for a finally-block might re-throw to top-level.
    // 2) External v8::TryCatch exists: Only create a message if the handler
    //    captures messages or is verbose (which reports despite the catch).
    // 3) ReThrow from v8::TryCatch: The message from a previous throw still
    //    exists and we preserve it instead of creating a new message.
    bool requires_message = try_catch_handler() == nullptr ||
                            try_catch_handler()->is_verbose_ ||
                            try_catch_handler()->capture_message_;
    bool rethrowing_message = thread_local_top()->rethrowing_message_;
  
    thread_local_top()->rethrowing_message_ = false;
  
    // Notify debugger of exception.
    if (is_catchable_by_javascript(raw_exception)) {
      base::Optional<Object> maybe_exception = debug()->OnThrow(exception);
      if (maybe_exception.has_value()) {
        return *maybe_exception;
      }
    }
  
    // Generate the message if required.
    if (requires_message && !rethrowing_message) {
      MessageLocation computed_location;
      // If no location was specified we try to use a computed one instead.
      if (location == nullptr && ComputeLocation(&computed_location)) {
        location = &computed_location;
      }
      if (bootstrapper()->IsActive()) {
        // It's not safe to try to make message objects or collect stack traces
        // while the bootstrapper is active since the infrastructure may not have
        // been properly initialized.
        ReportBootstrappingException(exception, location);
      } else {
        Handle<Object> message_obj = CreateMessageOrAbort(exception, location);
        thread_local_top()->pending_message_obj_ = *message_obj;
      }
    }
  
    // Set the exception being thrown.
    set_pending_exception(*exception);
    return ReadOnlyRoots(heap()).exception();
  }
  
  Object Isolate::ReThrow(Object exception) {
    DCHECK(!has_pending_exception());
  
    // Set the exception being re-thrown.
    set_pending_exception(exception);
    return ReadOnlyRoots(heap()).exception();
  }
  
  namespace {
  // This scope will set the thread-in-wasm flag after the execution of all
  // destructors. The thread-in-wasm flag is only set when the scope gets enabled.
  class SetThreadInWasmFlagScope {
   public:
    SetThreadInWasmFlagScope() {
      DCHECK_IMPLIES(trap_handler::IsTrapHandlerEnabled(),
                     !trap_handler::IsThreadInWasm());
    }
  
    ~SetThreadInWasmFlagScope() {
      if (enabled_) trap_handler::SetThreadInWasm();
    }
  
    void Enable() { enabled_ = true; }
  
   private:
    bool enabled_ = false;
  };
  }  // namespace
  
  Object Isolate::UnwindAndFindHandler() {
    // Create the {SetThreadInWasmFlagScope} first in this function so that its
    // destructor gets called after all the other destructors. It is important
    // that the destructor sets the thread-in-wasm flag after all other
    // destructors. The other destructors may cause exceptions, e.g. ASan on
    // Windows, which would invalidate the thread-in-wasm flag when the wasm trap
    // handler handles such non-wasm exceptions.
    SetThreadInWasmFlagScope set_thread_in_wasm_flag_scope;
    Object exception = pending_exception();
  
    auto FoundHandler = [&](Context context, Address instruction_start,
                            intptr_t handler_offset,
                            Address constant_pool_address, Address handler_sp,
                            Address handler_fp) {
      // Store information to be consumed by the CEntry.
      thread_local_top()->pending_handler_context_ = context;
      thread_local_top()->pending_handler_entrypoint_ =
          instruction_start + handler_offset;
      thread_local_top()->pending_handler_constant_pool_ = constant_pool_address;
      thread_local_top()->pending_handler_fp_ = handler_fp;
      thread_local_top()->pending_handler_sp_ = handler_sp;
  
      // Return and clear pending exception. The contract is that:
      // (1) the pending exception is stored in one place (no duplication), and
      // (2) within generated-code land, that one place is the return register.
      // If/when we unwind back into C++ (returning to the JSEntry stub,
      // or to Execution::CallWasm), the returned exception will be sent
      // back to isolate->set_pending_exception(...).
      clear_pending_exception();
      return exception;
    };
  
    // Special handling of termination exceptions, uncatchable by JavaScript and
    // Wasm code, we unwind the handlers until the top ENTRY handler is found.
    bool catchable_by_js = is_catchable_by_javascript(exception);
  
    // Compute handler and stack unwinding information by performing a full walk
    // over the stack and dispatching according to the frame type.
    for (StackFrameIterator iter(this);; iter.Advance()) {
      // Handler must exist.
      DCHECK(!iter.done());
  
      StackFrame* frame = iter.frame();
  
      switch (frame->type()) {
        case StackFrame::ENTRY:
        case StackFrame::CONSTRUCT_ENTRY: {
          // For JSEntry frames we always have a handler.
          StackHandler* handler = frame->top_handler();
  
          // Restore the next handler.
          thread_local_top()->handler_ = handler->next_address();
  
          // Gather information from the handler.
          Code code = frame->LookupCode();
          HandlerTable table(code);
          return FoundHandler(Context(), code.InstructionStart(this, frame->pc()),
                              table.LookupReturn(0), code.constant_pool(),
                              handler->address() + StackHandlerConstants::kSize,
                              0);
        }
  
  #if V8_ENABLE_WEBASSEMBLY
        case StackFrame::C_WASM_ENTRY: {
          StackHandler* handler = frame->top_handler();
          thread_local_top()->handler_ = handler->next_address();
          Code code = frame->LookupCode();
          HandlerTable table(code);
          Address instruction_start = code.InstructionStart(this, frame->pc());
          int return_offset = static_cast<int>(frame->pc() - instruction_start);
          int handler_offset = table.LookupReturn(return_offset);
          DCHECK_NE(-1, handler_offset);
          // Compute the stack pointer from the frame pointer. This ensures that
          // argument slots on the stack are dropped as returning would.
          Address return_sp = frame->fp() +
                              StandardFrameConstants::kFixedFrameSizeAboveFp -
                              code.stack_slots() * kSystemPointerSize;
          return FoundHandler(Context(), instruction_start, handler_offset,
                              code.constant_pool(), return_sp, frame->fp());
        }
  
        case StackFrame::WASM: {
          if (!is_catchable_by_wasm(exception)) break;
  
          // For WebAssembly frames we perform a lookup in the handler table.
          // This code ref scope is here to avoid a check failure when looking up
          // the code. It's not actually necessary to keep the code alive as it's
          // currently being executed.
          wasm::WasmCodeRefScope code_ref_scope;
          WasmFrame* wasm_frame = static_cast<WasmFrame*>(frame);
          wasm::WasmCode* wasm_code =
              wasm_engine()->code_manager()->LookupCode(frame->pc());
          int offset = wasm_frame->LookupExceptionHandlerInTable();
          if (offset < 0) break;
          wasm_engine()->SampleCatchEvent(this);
          // Compute the stack pointer from the frame pointer. This ensures that
          // argument slots on the stack are dropped as returning would.
          Address return_sp = frame->fp() +
                              StandardFrameConstants::kFixedFrameSizeAboveFp -
                              wasm_code->stack_slots() * kSystemPointerSize;
  
          // This is going to be handled by WebAssembly, so we need to set the TLS
          // flag. The {SetThreadInWasmFlagScope} will set the flag after all
          // destructors have been executed.
          set_thread_in_wasm_flag_scope.Enable();
          return FoundHandler(Context(), wasm_code->instruction_start(), offset,
                              wasm_code->constant_pool(), return_sp, frame->fp());
        }
  
        case StackFrame::WASM_COMPILE_LAZY: {
          // Can only fail directly on invocation. This happens if an invalid
          // function was validated lazily.
          DCHECK(FLAG_wasm_lazy_validation);
          break;
        }
  #endif  // V8_ENABLE_WEBASSEMBLY
  
        case StackFrame::OPTIMIZED: {
          // For optimized frames we perform a lookup in the handler table.
          if (!catchable_by_js) break;
          OptimizedFrame* js_frame = static_cast<OptimizedFrame*>(frame);
          Code code = frame->LookupCode();
          int offset = js_frame->LookupExceptionHandlerInTable(nullptr, nullptr);
          if (offset < 0) break;
          // Compute the stack pointer from the frame pointer. This ensures
          // that argument slots on the stack are dropped as returning would.
          Address return_sp = frame->fp() +
                              StandardFrameConstants::kFixedFrameSizeAboveFp -
                              code.stack_slots() * kSystemPointerSize;
  
          // TODO(bmeurer): Turbofanned BUILTIN frames appear as OPTIMIZED,
          // but do not have a code kind of TURBOFAN.
          if (CodeKindCanDeoptimize(code.kind()) &&
              code.marked_for_deoptimization()) {
            // If the target code is lazy deoptimized, we jump to the original
            // return address, but we make a note that we are throwing, so
            // that the deoptimizer can do the right thing.
            offset = static_cast<int>(frame->pc() - code.entry());
            set_deoptimizer_lazy_throw(true);
          }
  
          return FoundHandler(Context(), code.InstructionStart(this, frame->pc()),
                              offset, code.constant_pool(), return_sp,
                              frame->fp());
        }
  
        case StackFrame::STUB: {
          // Some stubs are able to handle exceptions.
          if (!catchable_by_js) break;
          StubFrame* stub_frame = static_cast<StubFrame*>(frame);
  #if defined(DEBUG) && V8_ENABLE_WEBASSEMBLY
          wasm::WasmCodeRefScope code_ref_scope;
          DCHECK_NULL(wasm_engine()->code_manager()->LookupCode(frame->pc()));
  #endif  // defined(DEBUG) && V8_ENABLE_WEBASSEMBLY
          Code code = stub_frame->LookupCode();
          if (!code.IsCode() || code.kind() != CodeKind::BUILTIN ||
              !code.has_handler_table() || !code.is_turbofanned()) {
            break;
          }
  
          int offset = stub_frame->LookupExceptionHandlerInTable();
          if (offset < 0) break;
  
          // Compute the stack pointer from the frame pointer. This ensures
          // that argument slots on the stack are dropped as returning would.
          Address return_sp = frame->fp() +
                              StandardFrameConstants::kFixedFrameSizeAboveFp -
                              code.stack_slots() * kSystemPointerSize;
  
          return FoundHandler(Context(), code.InstructionStart(this, frame->pc()),
                              offset, code.constant_pool(), return_sp,
                              frame->fp());
        }
  
        case StackFrame::INTERPRETED:
        case StackFrame::BASELINE: {
          // For interpreted frame we perform a range lookup in the handler table.
          if (!catchable_by_js) break;
          UnoptimizedFrame* js_frame = UnoptimizedFrame::cast(frame);
          int register_slots = UnoptimizedFrameConstants::RegisterStackSlotCount(
              js_frame->GetBytecodeArray().register_count());
          int context_reg = 0;  // Will contain register index holding context.
          int offset =
              js_frame->LookupExceptionHandlerInTable(&context_reg, nullptr);
          if (offset < 0) break;
          // Compute the stack pointer from the frame pointer. This ensures that
          // argument slots on the stack are dropped as returning would.
          // Note: This is only needed for interpreted frames that have been
          //       materialized by the deoptimizer. If there is a handler frame
          //       in between then {frame->sp()} would already be correct.
          Address return_sp = frame->fp() -
                              InterpreterFrameConstants::kFixedFrameSizeFromFp -
                              register_slots * kSystemPointerSize;
  
          // Patch the bytecode offset in the interpreted frame to reflect the
          // position of the exception handler. The special builtin below will
          // take care of continuing to dispatch at that position. Also restore
          // the correct context for the handler from the interpreter register.
          Context context =
              Context::cast(js_frame->ReadInterpreterRegister(context_reg));
          DCHECK(context.IsContext());
  
          if (frame->is_baseline()) {
            BaselineFrame* sp_frame = BaselineFrame::cast(js_frame);
            Code code = sp_frame->LookupCode();
            intptr_t pc_offset = sp_frame->GetPCForBytecodeOffset(offset);
            // Patch the context register directly on the frame, so that we don't
            // need to have a context read + write in the baseline code.
            sp_frame->PatchContext(context);
            return FoundHandler(
                Context(), code.InstructionStart(this, sp_frame->sp()), pc_offset,
                code.constant_pool(), return_sp, sp_frame->fp());
          } else {
            InterpretedFrame::cast(js_frame)->PatchBytecodeOffset(
                static_cast<int>(offset));
  
            Code code =
                builtins()->builtin(Builtins::kInterpreterEnterAtBytecode);
            return FoundHandler(context, code.InstructionStart(), 0,
                                code.constant_pool(), return_sp, frame->fp());
          }
        }
  
        case StackFrame::BUILTIN:
          // For builtin frames we are guaranteed not to find a handler.
          if (catchable_by_js) {
            CHECK_EQ(-1, BuiltinFrame::cast(frame)->LookupExceptionHandlerInTable(
                             nullptr, nullptr));
          }
          break;
  
        case StackFrame::JAVA_SCRIPT_BUILTIN_CONTINUATION_WITH_CATCH: {
          // Builtin continuation frames with catch can handle exceptions.
          if (!catchable_by_js) break;
          JavaScriptBuiltinContinuationWithCatchFrame* js_frame =
              JavaScriptBuiltinContinuationWithCatchFrame::cast(frame);
          js_frame->SetException(exception);
  
          // Reconstruct the stack pointer from the frame pointer.
          Address return_sp = js_frame->fp() - js_frame->GetSPToFPDelta();
          Code code = js_frame->LookupCode();
          return FoundHandler(Context(), code.InstructionStart(), 0,
                              code.constant_pool(), return_sp, frame->fp());
        } break;
  
        default:
          // All other types can not handle exception.
          break;
      }
  
      if (frame->is_optimized()) {
        // Remove per-frame stored materialized objects.
        bool removed = materialized_object_store_->Remove(frame->fp());
        USE(removed);
        // If there were any materialized objects, the code should be
        // marked for deopt.
        DCHECK_IMPLIES(removed, frame->LookupCode().marked_for_deoptimization());
      }
    }
  
    UNREACHABLE();
  }
  
  namespace {
  HandlerTable::CatchPrediction PredictException(JavaScriptFrame* frame) {
    HandlerTable::CatchPrediction prediction;
    if (frame->is_optimized()) {
      if (frame->LookupExceptionHandlerInTable(nullptr, nullptr) > 0) {
        // This optimized frame will catch. It's handler table does not include
        // exception prediction, and we need to use the corresponding handler
        // tables on the unoptimized code objects.
        std::vector<FrameSummary> summaries;
        frame->Summarize(&summaries);
        for (size_t i = summaries.size(); i != 0; i--) {
          const FrameSummary& summary = summaries[i - 1];
          Handle<AbstractCode> code = summary.AsJavaScript().abstract_code();
          if (code->IsCode() && code->kind() == CodeKind::BUILTIN) {
            prediction = code->GetCode().GetBuiltinCatchPrediction();
            if (prediction == HandlerTable::UNCAUGHT) continue;
            return prediction;
          }
  
          // Must have been constructed from a bytecode array.
          CHECK_EQ(CodeKind::INTERPRETED_FUNCTION, code->kind());
          int code_offset = summary.code_offset();
          HandlerTable table(code->GetBytecodeArray());
          int index = table.LookupRange(code_offset, nullptr, &prediction);
          if (index <= 0) continue;
          if (prediction == HandlerTable::UNCAUGHT) continue;
          return prediction;
        }
      }
    } else if (frame->LookupExceptionHandlerInTable(nullptr, &prediction) > 0) {
      return prediction;
    }
    return HandlerTable::UNCAUGHT;
  }
  
  Isolate::CatchType ToCatchType(HandlerTable::CatchPrediction prediction) {
    switch (prediction) {
      case HandlerTable::UNCAUGHT:
        return Isolate::NOT_CAUGHT;
      case HandlerTable::CAUGHT:
        return Isolate::CAUGHT_BY_JAVASCRIPT;
      case HandlerTable::PROMISE:
        return Isolate::CAUGHT_BY_PROMISE;
      case HandlerTable::DESUGARING:
        return Isolate::CAUGHT_BY_DESUGARING;
      case HandlerTable::UNCAUGHT_ASYNC_AWAIT:
      case HandlerTable::ASYNC_AWAIT:
        return Isolate::CAUGHT_BY_ASYNC_AWAIT;
      default:
        UNREACHABLE();
    }
  }
  }  // anonymous namespace
  
  Isolate::CatchType Isolate::PredictExceptionCatcher() {
    Address external_handler = thread_local_top()->try_catch_handler_address();
    if (IsExternalHandlerOnTop(Object())) return CAUGHT_BY_EXTERNAL;
  
    // Search for an exception handler by performing a full walk over the stack.
    for (StackFrameIterator iter(this); !iter.done(); iter.Advance()) {
      StackFrame* frame = iter.frame();
  
      switch (frame->type()) {
        case StackFrame::ENTRY:
        case StackFrame::CONSTRUCT_ENTRY: {
          Address entry_handler = frame->top_handler()->next_address();
          // The exception has been externally caught if and only if there is an
          // external handler which is on top of the top-most JS_ENTRY handler.
          if (external_handler != kNullAddress &&
              !try_catch_handler()->is_verbose_) {
            if (entry_handler == kNullAddress ||
                entry_handler > external_handler) {
              return CAUGHT_BY_EXTERNAL;
            }
          }
        } break;
  
        // For JavaScript frames we perform a lookup in the handler table.
        case StackFrame::OPTIMIZED:
        case StackFrame::INTERPRETED:
        case StackFrame::BASELINE:
        case StackFrame::BUILTIN: {
          JavaScriptFrame* js_frame = JavaScriptFrame::cast(frame);
          Isolate::CatchType prediction = ToCatchType(PredictException(js_frame));
          if (prediction == NOT_CAUGHT) break;
          return prediction;
        } break;
  
        case StackFrame::STUB: {
          Handle<Code> code(frame->LookupCode(), this);
          if (!code->IsCode() || code->kind() != CodeKind::BUILTIN ||
              !code->has_handler_table() || !code->is_turbofanned()) {
            break;
          }
  
          CatchType prediction = ToCatchType(code->GetBuiltinCatchPrediction());
          if (prediction != NOT_CAUGHT) return prediction;
        } break;
  
        case StackFrame::JAVA_SCRIPT_BUILTIN_CONTINUATION_WITH_CATCH: {
          Handle<Code> code(frame->LookupCode(), this);
          CatchType prediction = ToCatchType(code->GetBuiltinCatchPrediction());
          if (prediction != NOT_CAUGHT) return prediction;
        } break;
  
        default:
          // All other types can not handle exception.
          break;
      }
    }
  
    // Handler not found.
    return NOT_CAUGHT;
  }
  
  Object Isolate::ThrowIllegalOperation() {
    if (FLAG_stack_trace_on_illegal) PrintStack(stdout);
    return Throw(ReadOnlyRoots(heap()).illegal_access_string());
  }
  
  void Isolate::ScheduleThrow(Object exception) {
    // When scheduling a throw we first throw the exception to get the
    // error reporting if it is uncaught before rescheduling it.
    Throw(exception);
    PropagatePendingExceptionToExternalTryCatch();
    if (has_pending_exception()) {
      thread_local_top()->scheduled_exception_ = pending_exception();
      thread_local_top()->external_caught_exception_ = false;
      clear_pending_exception();
    }
  }
  
  void Isolate::RestorePendingMessageFromTryCatch(v8::TryCatch* handler) {
    DCHECK(handler == try_catch_handler());
    DCHECK(handler->HasCaught());
    DCHECK(handler->rethrow_);
    DCHECK(handler->capture_message_);
    Object message(reinterpret_cast<Address>(handler->message_obj_));
    DCHECK(message.IsJSMessageObject() || message.IsTheHole(this));
    thread_local_top()->pending_message_obj_ = message;
  }
  
  void Isolate::CancelScheduledExceptionFromTryCatch(v8::TryCatch* handler) {
    DCHECK(has_scheduled_exception());
    if (reinterpret_cast<void*>(scheduled_exception().ptr()) ==
        handler->exception_) {
      DCHECK_NE(scheduled_exception(),
                ReadOnlyRoots(heap()).termination_exception());
      clear_scheduled_exception();
    } else {
      DCHECK_EQ(scheduled_exception(),
                ReadOnlyRoots(heap()).termination_exception());
      // Clear termination once we returned from all V8 frames.
      if (thread_local_top()->CallDepthIsZero()) {
        thread_local_top()->external_caught_exception_ = false;
        clear_scheduled_exception();
      }
    }
    if (reinterpret_cast<void*>(thread_local_top()->pending_message_obj_.ptr()) ==
        handler->message_obj_) {
      clear_pending_message();
    }
  }
  
  Object Isolate::PromoteScheduledException() {
    Object thrown = scheduled_exception();
    clear_scheduled_exception();
    // Re-throw the exception to avoid getting repeated error reporting.
    return ReThrow(thrown);
  }
  
  void Isolate::PrintCurrentStackTrace(FILE* out) {
    CaptureStackTraceOptions options;
    options.limit = 0;
    options.skip_mode = SKIP_NONE;
    options.capture_builtin_exit_frames = true;
    options.async_stack_trace = FLAG_async_stack_traces;
    options.filter_mode = StackTraceBuilder::CURRENT_SECURITY_CONTEXT;
    options.capture_only_frames_subject_to_debugging = false;
  
    Handle<FixedArray> frames =
        CaptureStackTrace(this, this->factory()->undefined_value(), options);
  
    IncrementalStringBuilder builder(this);
    for (int i = 0; i < frames->length(); ++i) {
      Handle<StackFrameInfo> frame(StackFrameInfo::cast(frames->get(i)), this);
      SerializeStackFrameInfo(this, frame, &builder);
    }
  
    Handle<String> stack_trace = builder.Finish().ToHandleChecked();
    stack_trace->PrintOn(out);
  }
  
  bool Isolate::ComputeLocation(MessageLocation* target) {
    StackTraceFrameIterator it(this);
    if (it.done()) return false;
    CommonFrame* frame = it.frame();
    // Compute the location from the function and the relocation info of the
    // baseline code. For optimized code this will use the deoptimization
    // information to get canonical location information.
    std::vector<FrameSummary> frames;
  #if V8_ENABLE_WEBASSEMBLY
    wasm::WasmCodeRefScope code_ref_scope;
  #endif  // V8_ENABLE_WEBASSEMBLY
    frame->Summarize(&frames);
    FrameSummary& summary = frames.back();
    Handle<SharedFunctionInfo> shared;
    Handle<Object> script = summary.script();
    if (!script->IsScript() ||
        (Script::cast(*script).source().IsUndefined(this))) {
      return false;
    }
  
    if (summary.IsJavaScript()) {
      shared = handle(summary.AsJavaScript().function()->shared(), this);
    }
    if (summary.AreSourcePositionsAvailable()) {
      int pos = summary.SourcePosition();
      *target =
          MessageLocation(Handle<Script>::cast(script), pos, pos + 1, shared);
    } else {
      *target = MessageLocation(Handle<Script>::cast(script), shared,
                                summary.code_offset());
    }
    return true;
  }
  
  bool Isolate::ComputeLocationFromException(MessageLocation* target,
                                             Handle<Object> exception) {
    if (!exception->IsJSObject()) return false;
  
    Handle<Name> start_pos_symbol = factory()->error_start_pos_symbol();
    Handle<Object> start_pos = JSReceiver::GetDataProperty(
        Handle<JSObject>::cast(exception), start_pos_symbol);
    if (!start_pos->IsSmi()) return false;
    int start_pos_value = Handle<Smi>::cast(start_pos)->value();
  
    Handle<Name> end_pos_symbol = factory()->error_end_pos_symbol();
    Handle<Object> end_pos = JSReceiver::GetDataProperty(
        Handle<JSObject>::cast(exception), end_pos_symbol);
    if (!end_pos->IsSmi()) return false;
    int end_pos_value = Handle<Smi>::cast(end_pos)->value();
  
    Handle<Name> script_symbol = factory()->error_script_symbol();
    Handle<Object> script = JSReceiver::GetDataProperty(
        Handle<JSObject>::cast(exception), script_symbol);
    if (!script->IsScript()) return false;
  
    Handle<Script> cast_script(Script::cast(*script), this);
    *target = MessageLocation(cast_script, start_pos_value, end_pos_value);
    return true;
  }
  
  bool Isolate::ComputeLocationFromStackTrace(MessageLocation* target,
                                              Handle<Object> exception) {
    if (!exception->IsJSObject()) return false;
    Handle<Name> key = factory()->stack_trace_symbol();
    Handle<Object> property =
        JSReceiver::GetDataProperty(Handle<JSObject>::cast(exception), key);
    if (!property->IsFixedArray()) return false;
    Handle<FixedArray> stack = Handle<FixedArray>::cast(property);
    for (int i = 0; i < stack->length(); i++) {
      Handle<StackFrameInfo> frame(StackFrameInfo::cast(stack->get(i)), this);
      if (StackFrameInfo::ComputeLocation(frame, target)) return true;
    }
    return false;
  }
  
  Handle<JSMessageObject> Isolate::CreateMessage(Handle<Object> exception,
                                                 MessageLocation* location) {
    Handle<FixedArray> stack_trace_object;
    if (capture_stack_trace_for_uncaught_exceptions_) {
      if (exception->IsJSError()) {
        // We fetch the stack trace that corresponds to this error object.
        // If the lookup fails, the exception is probably not a valid Error
        // object. In that case, we fall through and capture the stack trace
        // at this throw site.
        stack_trace_object =
            GetDetailedStackTrace(Handle<JSObject>::cast(exception));
      }
      if (stack_trace_object.is_null()) {
        // Not an error object, we capture stack and location at throw site.
        stack_trace_object = CaptureCurrentStackTrace(
            stack_trace_for_uncaught_exceptions_frame_limit_,
            stack_trace_for_uncaught_exceptions_options_);
      }
    }
    MessageLocation computed_location;
    if (location == nullptr &&
        (ComputeLocationFromException(&computed_location, exception) ||
         ComputeLocationFromStackTrace(&computed_location, exception) ||
         ComputeLocation(&computed_location))) {
      location = &computed_location;
    }
  
    return MessageHandler::MakeMessageObject(
        this, MessageTemplate::kUncaughtException, location, exception,
        stack_trace_object);
  }
  
  bool Isolate::IsJavaScriptHandlerOnTop(Object exception) {
    DCHECK_NE(ReadOnlyRoots(heap()).the_hole_value(), exception);
  
    // For uncatchable exceptions, the JavaScript handler cannot be on top.
    if (!is_catchable_by_javascript(exception)) return false;
  
    // Get the top-most JS_ENTRY handler, cannot be on top if it doesn't exist.
    Address entry_handler = Isolate::handler(thread_local_top());
    if (entry_handler == kNullAddress) return false;
  
    // Get the address of the external handler so we can compare the address to
    // determine which one is closer to the top of the stack.
    Address external_handler = thread_local_top()->try_catch_handler_address();
    if (external_handler == kNullAddress) return true;
  
    // The exception has been externally caught if and only if there is an
    // external handler which is on top of the top-most JS_ENTRY handler.
    //
    // Note, that finally clauses would re-throw an exception unless it's aborted
    // by jumps in control flow (like return, break, etc.) and we'll have another
    // chance to set proper v8::TryCatch later.
    return (entry_handler < external_handler);
  }
  
  bool Isolate::IsExternalHandlerOnTop(Object exception) {
    DCHECK_NE(ReadOnlyRoots(heap()).the_hole_value(), exception);
  
    // Get the address of the external handler so we can compare the address to
    // determine which one is closer to the top of the stack.
    Address external_handler = thread_local_top()->try_catch_handler_address();
    if (external_handler == kNullAddress) return false;
  
    // For uncatchable exceptions, the external handler is always on top.
    if (!is_catchable_by_javascript(exception)) return true;
  
    // Get the top-most JS_ENTRY handler, cannot be on top if it doesn't exist.
    Address entry_handler = Isolate::handler(thread_local_top());
    if (entry_handler == kNullAddress) return true;
  
    // The exception has been externally caught if and only if there is an
    // external handler which is on top of the top-most JS_ENTRY handler.
    //
    // Note, that finally clauses would re-throw an exception unless it's aborted
    // by jumps in control flow (like return, break, etc.) and we'll have another
    // chance to set proper v8::TryCatch later.
    return (entry_handler > external_handler);
  }
  
  std::vector<MemoryRange>* Isolate::GetCodePages() const {
    return code_pages_.load(std::memory_order_acquire);
  }
  
  void Isolate::SetCodePages(std::vector<MemoryRange>* new_code_pages) {
    code_pages_.store(new_code_pages, std::memory_order_release);
  }
  
  void Isolate::ReportPendingMessages() {
    DCHECK(AllowExceptions::IsAllowed(this));
  
    // The embedder might run script in response to an exception.
    AllowJavascriptExecutionDebugOnly allow_script(this);
  
    Object exception_obj = pending_exception();
  
    // Try to propagate the exception to an external v8::TryCatch handler. If
    // propagation was unsuccessful, then we will get another chance at reporting
    // the pending message if the exception is re-thrown.
    bool has_been_propagated = PropagatePendingExceptionToExternalTryCatch();
    if (!has_been_propagated) return;
  
    // Clear the pending message object early to avoid endless recursion.
    Object message_obj = thread_local_top()->pending_message_obj_;
    clear_pending_message();
  
    // For uncatchable exceptions we do nothing. If needed, the exception and the
    // message have already been propagated to v8::TryCatch.
    if (!is_catchable_by_javascript(exception_obj)) return;
  
    // Determine whether the message needs to be reported to all message handlers
    // depending on whether and external v8::TryCatch or an internal JavaScript
    // handler is on top.
    bool should_report_exception;
    if (IsExternalHandlerOnTop(exception_obj)) {
      // Only report the exception if the external handler is verbose.
      should_report_exception = try_catch_handler()->is_verbose_;
    } else {
      // Report the exception if it isn't caught by JavaScript code.
      should_report_exception = !IsJavaScriptHandlerOnTop(exception_obj);
    }
  
    // Actually report the pending message to all message handlers.
    if (!message_obj.IsTheHole(this) && should_report_exception) {
      HandleScope scope(this);
      Handle<JSMessageObject> message(JSMessageObject::cast(message_obj), this);
      Handle<Object> exception(exception_obj, this);
      Handle<Script> script(message->script(), this);
      // Clear the exception and restore it afterwards, otherwise
      // CollectSourcePositions will abort.
      clear_pending_exception();
      JSMessageObject::EnsureSourcePositionsAvailable(this, message);
      set_pending_exception(*exception);
      int start_pos = message->GetStartPosition();
      int end_pos = message->GetEndPosition();
      MessageLocation location(script, start_pos, end_pos);
      MessageHandler::ReportMessage(this, &location, message);
    }
  }
  
  bool Isolate::OptionalRescheduleException(bool clear_exception) {
    DCHECK(has_pending_exception());
    PropagatePendingExceptionToExternalTryCatch();
  
    bool is_termination_exception =
        pending_exception() == ReadOnlyRoots(this).termination_exception();
  
    if (is_termination_exception) {
      if (clear_exception) {
        thread_local_top()->external_caught_exception_ = false;
        clear_pending_exception();
        return false;
      }
    } else if (thread_local_top()->external_caught_exception_) {
      // If the exception is externally caught, clear it if there are no
      // JavaScript frames on the way to the C++ frame that has the
      // external handler.
      DCHECK_NE(thread_local_top()->try_catch_handler_address(), kNullAddress);
      Address external_handler_address =
          thread_local_top()->try_catch_handler_address();
      JavaScriptFrameIterator it(this);
      if (it.done() || (it.frame()->sp() > external_handler_address)) {
        clear_exception = true;
      }
    }
  
    // Clear the exception if needed.
    if (clear_exception) {
      thread_local_top()->external_caught_exception_ = false;
      clear_pending_exception();
      return false;
    }
  
    // Reschedule the exception.
    thread_local_top()->scheduled_exception_ = pending_exception();
    clear_pending_exception();
    return true;
  }
  
  void Isolate::PushPromise(Handle<JSObject> promise) {
    ThreadLocalTop* tltop = thread_local_top();
    PromiseOnStack* prev = tltop->promise_on_stack_;
    Handle<JSObject> global_promise = global_handles()->Create(*promise);
    tltop->promise_on_stack_ = new PromiseOnStack(global_promise, prev);
  }
  
  void Isolate::PopPromise() {
    ThreadLocalTop* tltop = thread_local_top();
    if (tltop->promise_on_stack_ == nullptr) return;
    PromiseOnStack* prev = tltop->promise_on_stack_->prev();
    Handle<Object> global_promise = tltop->promise_on_stack_->promise();
    delete tltop->promise_on_stack_;
    tltop->promise_on_stack_ = prev;
    global_handles()->Destroy(global_promise.location());
  }
  
  namespace {
  bool PromiseIsRejectHandler(Isolate* isolate, Handle<JSReceiver> handler) {
    // Recurse to the forwarding Promise (e.g. return false) due to
    //  - await reaction forwarding to the throwaway Promise, which has
    //    a dependency edge to the outer Promise.
    //  - PromiseIdResolveHandler forwarding to the output of .then
    //  - Promise.all/Promise.race forwarding to a throwaway Promise, which
    //    has a dependency edge to the generated outer Promise.
    // Otherwise, this is a real reject handler for the Promise.
    Handle<Symbol> key = isolate->factory()->promise_forwarding_handler_symbol();
    Handle<Object> forwarding_handler = JSReceiver::GetDataProperty(handler, key);
    return forwarding_handler->IsUndefined(isolate);
  }
  
  bool PromiseHasUserDefinedRejectHandlerInternal(Isolate* isolate,
                                                  Handle<JSPromise> promise) {
    Handle<Object> current(promise->reactions(), isolate);
    while (!current->IsSmi()) {
      Handle<PromiseReaction> reaction = Handle<PromiseReaction>::cast(current);
      Handle<HeapObject> promise_or_capability(reaction->promise_or_capability(),
                                               isolate);
      if (!promise_or_capability->IsUndefined(isolate)) {
        if (!promise_or_capability->IsJSPromise()) {
          promise_or_capability = handle(
              Handle<PromiseCapability>::cast(promise_or_capability)->promise(),
              isolate);
        }
        Handle<JSPromise> promise =
            Handle<JSPromise>::cast(promise_or_capability);
        if (!reaction->reject_handler().IsUndefined(isolate)) {
          Handle<JSReceiver> reject_handler(
              JSReceiver::cast(reaction->reject_handler()), isolate);
          if (PromiseIsRejectHandler(isolate, reject_handler)) return true;
        }
        if (isolate->PromiseHasUserDefinedRejectHandler(promise)) return true;
      }
      current = handle(reaction->next(), isolate);
    }
    return false;
  }
  
  }  // namespace
  
  bool Isolate::PromiseHasUserDefinedRejectHandler(Handle<JSPromise> promise) {
    Handle<Symbol> key = factory()->promise_handled_by_symbol();
    std::stack<Handle<JSPromise>> promises;
    // First descend into the outermost promise and collect the stack of
    // Promises for reverse processing.
    while (true) {
      // If this promise was marked as being handled by a catch block
      // in an async function, then it has a user-defined reject handler.
      if (promise->handled_hint()) return true;
      if (promise->status() == Promise::kPending) {
        promises.push(promise);
      }
      Handle<Object> outer_promise_obj = JSObject::GetDataProperty(promise, key);
      if (!outer_promise_obj->IsJSPromise()) break;
      promise = Handle<JSPromise>::cast(outer_promise_obj);
    }
  
    while (!promises.empty()) {
      promise = promises.top();
      if (PromiseHasUserDefinedRejectHandlerInternal(this, promise)) return true;
      promises.pop();
    }
    return false;
  }
  
  Handle<Object> Isolate::GetPromiseOnStackOnThrow() {
    Handle<Object> undefined = factory()->undefined_value();
    ThreadLocalTop* tltop = thread_local_top();
    if (tltop->promise_on_stack_ == nullptr) return undefined;
    // Find the top-most try-catch or try-finally handler.
    CatchType prediction = PredictExceptionCatcher();
    if (prediction == NOT_CAUGHT || prediction == CAUGHT_BY_EXTERNAL) {
      return undefined;
    }
    Handle<Object> retval = undefined;
    PromiseOnStack* promise_on_stack = tltop->promise_on_stack_;
    for (StackFrameIterator it(this); !it.done(); it.Advance()) {
      StackFrame* frame = it.frame();
      HandlerTable::CatchPrediction catch_prediction;
      if (frame->is_java_script()) {
        catch_prediction = PredictException(JavaScriptFrame::cast(frame));
      } else if (frame->type() == StackFrame::STUB) {
        Code code = frame->LookupCode();
        if (!code.IsCode() || code.kind() != CodeKind::BUILTIN ||
            !code.has_handler_table() || !code.is_turbofanned()) {
          continue;
        }
        catch_prediction = code.GetBuiltinCatchPrediction();
      } else {
        continue;
      }
  
      switch (catch_prediction) {
        case HandlerTable::UNCAUGHT:
          continue;
        case HandlerTable::CAUGHT:
        case HandlerTable::DESUGARING:
          if (retval->IsJSPromise()) {
            // Caught the result of an inner async/await invocation.
            // Mark the inner promise as caught in the "synchronous case" so
            // that Debug::OnException will see. In the synchronous case,
            // namely in the code in an async function before the first
            // await, the function which has this exception event has not yet
            // returned, so the generated Promise has not yet been marked
            // by AsyncFunctionAwaitCaught with promiseHandledHintSymbol.
            Handle<JSPromise>::cast(retval)->set_handled_hint(true);
          }
          return retval;
        case HandlerTable::PROMISE:
          return promise_on_stack
                     ? Handle<Object>::cast(promise_on_stack->promise())
                     : undefined;
        case HandlerTable::UNCAUGHT_ASYNC_AWAIT:
        case HandlerTable::ASYNC_AWAIT: {
          // If in the initial portion of async/await, continue the loop to pop up
          // successive async/await stack frames until an asynchronous one with
          // dependents is found, or a non-async stack frame is encountered, in
          // order to handle the synchronous async/await catch prediction case:
          // assume that async function calls are awaited.
          if (!promise_on_stack) return retval;
          retval = promise_on_stack->promise();
          if (retval->IsJSPromise()) {
            if (PromiseHasUserDefinedRejectHandler(
                    Handle<JSPromise>::cast(retval))) {
              return retval;
            }
          }
          promise_on_stack = promise_on_stack->prev();
          continue;
        }
      }
    }
    return retval;
  }
  
  void Isolate::SetCaptureStackTraceForUncaughtExceptions(
      bool capture, int frame_limit, StackTrace::StackTraceOptions options) {
    capture_stack_trace_for_uncaught_exceptions_ = capture;
    stack_trace_for_uncaught_exceptions_frame_limit_ = frame_limit;
    stack_trace_for_uncaught_exceptions_options_ = options;
  }
  
  bool Isolate::get_capture_stack_trace_for_uncaught_exceptions() const {
    return capture_stack_trace_for_uncaught_exceptions_;
  }
  
  void Isolate::SetAbortOnUncaughtExceptionCallback(
      v8::Isolate::AbortOnUncaughtExceptionCallback callback) {
    abort_on_uncaught_exception_callback_ = callback;
  }
  
  void Isolate::InstallConditionalFeatures(Handle<Context> context) {
    Handle<JSGlobalObject> global = handle(context->global_object(), this);
    Handle<String> sab_name = factory()->SharedArrayBuffer_string();
    if (!JSReceiver::HasProperty(global, sab_name).FromMaybe(true)) {
      if (IsSharedArrayBufferConstructorEnabled(context)) {
        JSObject::AddProperty(this, global, factory()->SharedArrayBuffer_string(),
                              shared_array_buffer_fun(), DONT_ENUM);
      }
    }
  }
  
  bool Isolate::IsSharedArrayBufferConstructorEnabled(Handle<Context> context) {
    if (!FLAG_harmony_sharedarraybuffer) return false;
  
    if (!FLAG_enable_sharedarraybuffer_per_context) return true;
  
    if (sharedarraybuffer_constructor_enabled_callback()) {
      v8::Local<v8::Context> api_context = v8::Utils::ToLocal(context);
      return sharedarraybuffer_constructor_enabled_callback()(api_context);
    }
    return false;
  }
  
  bool Isolate::IsWasmSimdEnabled(Handle<Context> context) {
  #if V8_ENABLE_WEBASSEMBLY
    if (wasm_simd_enabled_callback()) {
      v8::Local<v8::Context> api_context = v8::Utils::ToLocal(context);
      return wasm_simd_enabled_callback()(api_context);
    }
    return FLAG_experimental_wasm_simd;
  #else
    return false;
  #endif  // V8_ENABLE_WEBASSEMBLY
  }
  
  bool Isolate::AreWasmExceptionsEnabled(Handle<Context> context) {
  #if V8_ENABLE_WEBASSEMBLY
    if (wasm_exceptions_enabled_callback()) {
      v8::Local<v8::Context> api_context = v8::Utils::ToLocal(context);
      return wasm_exceptions_enabled_callback()(api_context);
    }
    return FLAG_experimental_wasm_eh;
  #else
    return false;
  #endif  // V8_ENABLE_WEBASSEMBLY
  }
  
  Handle<Context> Isolate::GetIncumbentContext() {
    JavaScriptFrameIterator it(this);
  
    // 1st candidate: most-recently-entered author function's context
    // if it's newer than the last Context::BackupIncumbentScope entry.
    //
    // NOTE: This code assumes that the stack grows downward.
    Address top_backup_incumbent =
        top_backup_incumbent_scope()
            ? top_backup_incumbent_scope()->JSStackComparableAddress()
            : 0;
    if (!it.done() &&
        (!top_backup_incumbent || it.frame()->sp() < top_backup_incumbent)) {
      Context context = Context::cast(it.frame()->context());
      return Handle<Context>(context.native_context(), this);
    }
  
    // 2nd candidate: the last Context::Scope's incumbent context if any.
    if (top_backup_incumbent_scope()) {
      return Utils::OpenHandle(
          *top_backup_incumbent_scope()->backup_incumbent_context_);
    }
  
    // Last candidate: the entered context or microtask context.
    // Given that there is no other author function is running, there must be
    // no cross-context function running, then the incumbent realm must match
    // the entry realm.
    v8::Local<v8::Context> entered_context =
        reinterpret_cast<v8::Isolate*>(this)->GetEnteredOrMicrotaskContext();
    return Utils::OpenHandle(*entered_context);
  }
  
  char* Isolate::ArchiveThread(char* to) {
    MemCopy(to, reinterpret_cast<char*>(thread_local_top()),
            sizeof(ThreadLocalTop));
    return to + sizeof(ThreadLocalTop);
  }
  
  char* Isolate::RestoreThread(char* from) {
    MemCopy(reinterpret_cast<char*>(thread_local_top()), from,
            sizeof(ThreadLocalTop));
    DCHECK(context().is_null() || context().IsContext());
    return from + sizeof(ThreadLocalTop);
  }
  
  void Isolate::ReleaseSharedPtrs() {
    base::MutexGuard lock(&managed_ptr_destructors_mutex_);
    while (managed_ptr_destructors_head_) {
      ManagedPtrDestructor* l = managed_ptr_destructors_head_;
      ManagedPtrDestructor* n = nullptr;
      managed_ptr_destructors_head_ = nullptr;
      for (; l != nullptr; l = n) {
        l->destructor_(l->shared_ptr_ptr_);
        n = l->next_;
        delete l;
      }
    }
  }
  
  bool Isolate::IsBuiltinsTableHandleLocation(Address* handle_location) {
    FullObjectSlot location(handle_location);
    FullObjectSlot first_root(builtins_table());
    FullObjectSlot last_root(builtins_table() + Builtins::builtin_count);
    if (location >= last_root) return false;
    if (location < first_root) return false;
    return true;
  }
  
  void Isolate::RegisterManagedPtrDestructor(ManagedPtrDestructor* destructor) {
    base::MutexGuard lock(&managed_ptr_destructors_mutex_);
    DCHECK_NULL(destructor->prev_);
    DCHECK_NULL(destructor->next_);
    if (managed_ptr_destructors_head_) {
      managed_ptr_destructors_head_->prev_ = destructor;
    }
    destructor->next_ = managed_ptr_destructors_head_;
    managed_ptr_destructors_head_ = destructor;
  }
  
  void Isolate::UnregisterManagedPtrDestructor(ManagedPtrDestructor* destructor) {
    base::MutexGuard lock(&managed_ptr_destructors_mutex_);
    if (destructor->prev_) {
      destructor->prev_->next_ = destructor->next_;
    } else {
      DCHECK_EQ(destructor, managed_ptr_destructors_head_);
      managed_ptr_destructors_head_ = destructor->next_;
    }
    if (destructor->next_) destructor->next_->prev_ = destructor->prev_;
    destructor->prev_ = nullptr;
    destructor->next_ = nullptr;
  }
  
  #if V8_ENABLE_WEBASSEMBLY
  void Isolate::SetWasmEngine(wasm::WasmEngine* engine) {
    DCHECK_NULL(wasm_engine_);  // Only call once before {Init}.
    DCHECK_NOT_NULL(engine);
    wasm_engine_ = engine;
    wasm_engine_->AddIsolate(this);
  }
  
  void Isolate::AddSharedWasmMemory(Handle<WasmMemoryObject> memory_object) {
    HandleScope scope(this);
    Handle<WeakArrayList> shared_wasm_memories =
        factory()->shared_wasm_memories();
    shared_wasm_memories = WeakArrayList::AddToEnd(
        this, shared_wasm_memories, MaybeObjectHandle::Weak(memory_object));
    heap()->set_shared_wasm_memories(*shared_wasm_memories);
  }
  #endif  // V8_ENABLE_WEBASSEMBLY
  
  Isolate::PerIsolateThreadData::~PerIsolateThreadData() {
  #if defined(USE_SIMULATOR)
    delete simulator_;
  #endif
  }
  
  Isolate::PerIsolateThreadData* Isolate::ThreadDataTable::Lookup(
      ThreadId thread_id) {
    auto t = table_.find(thread_id);
    if (t == table_.end()) return nullptr;
    return t->second;
  }
  
  void Isolate::ThreadDataTable::Insert(Isolate::PerIsolateThreadData* data) {
    bool inserted = table_.insert(std::make_pair(data->thread_id_, data)).second;
    CHECK(inserted);
  }
  
  void Isolate::ThreadDataTable::Remove(PerIsolateThreadData* data) {
    table_.erase(data->thread_id_);
    delete data;
  }
  
  void Isolate::ThreadDataTable::RemoveAllThreads() {
    for (auto& x : table_) {
      delete x.second;
    }
    table_.clear();
  }
  
  class TracingAccountingAllocator : public AccountingAllocator {
   public:
    explicit TracingAccountingAllocator(Isolate* isolate) : isolate_(isolate) {}
    ~TracingAccountingAllocator() = default;
  
   protected:
    void TraceAllocateSegmentImpl(v8::internal::Segment* segment) override {
      base::MutexGuard lock(&mutex_);
      UpdateMemoryTrafficAndReportMemoryUsage(segment->total_size());
    }
  
    void TraceZoneCreationImpl(const Zone* zone) override {
      base::MutexGuard lock(&mutex_);
      active_zones_.insert(zone);
      nesting_depth_++;
    }
  
    void TraceZoneDestructionImpl(const Zone* zone) override {
      base::MutexGuard lock(&mutex_);
  #ifdef V8_ENABLE_PRECISE_ZONE_STATS
      if (FLAG_trace_zone_type_stats) {
        type_stats_.MergeWith(zone->type_stats());
      }
  #endif
      UpdateMemoryTrafficAndReportMemoryUsage(zone->segment_bytes_allocated());
      active_zones_.erase(zone);
      nesting_depth_--;
  
  #ifdef V8_ENABLE_PRECISE_ZONE_STATS
      if (FLAG_trace_zone_type_stats && active_zones_.empty()) {
        type_stats_.Dump();
      }
  #endif
    }
  
   private:
    void UpdateMemoryTrafficAndReportMemoryUsage(size_t memory_traffic_delta) {
      if (!FLAG_trace_zone_stats &&
          !(TracingFlags::zone_stats.load(std::memory_order_relaxed) &
            v8::tracing::TracingCategoryObserver::ENABLED_BY_TRACING)) {
        // Don't print anything if the zone tracing was enabled only because of
        // FLAG_trace_zone_type_stats.
        return;
      }
  
      memory_traffic_since_last_report_ += memory_traffic_delta;
      if (memory_traffic_since_last_report_ < FLAG_zone_stats_tolerance) return;
      memory_traffic_since_last_report_ = 0;
  
      Dump(buffer_, true);
  
      {
        std::string trace_str = buffer_.str();
  
        if (FLAG_trace_zone_stats) {
          PrintF(
              "{"
              "\"type\": \"v8-zone-trace\", "
              "\"stats\": %s"
              "}\n",
              trace_str.c_str());
        }
        if (V8_UNLIKELY(
                TracingFlags::zone_stats.load(std::memory_order_relaxed) &
                v8::tracing::TracingCategoryObserver::ENABLED_BY_TRACING)) {
          TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("v8.zone_stats"),
                               "V8.Zone_Stats", TRACE_EVENT_SCOPE_THREAD, "stats",
                               TRACE_STR_COPY(trace_str.c_str()));
        }
      }
  
      // Clear the buffer.
      buffer_.str(std::string());
    }
  
    void Dump(std::ostringstream& out, bool dump_details) {
      // Note: Neither isolate nor zones are locked, so be careful with accesses
      // as the allocator is potentially used on a concurrent thread.
      double time = isolate_->time_millis_since_init();
      out << "{"
          << "\"isolate\": \"" << reinterpret_cast<void*>(isolate_) << "\", "
          << "\"time\": " << time << ", ";
      size_t total_segment_bytes_allocated = 0;
      size_t total_zone_allocation_size = 0;
      size_t total_zone_freed_size = 0;
  
      if (dump_details) {
        // Print detailed zone stats if memory usage changes direction.
        out << "\"zones\": [";
        bool first = true;
        for (const Zone* zone : active_zones_) {
          size_t zone_segment_bytes_allocated = zone->segment_bytes_allocated();
          size_t zone_allocation_size = zone->allocation_size_for_tracing();
          size_t freed_size = zone->freed_size_for_tracing();
          if (first) {
            first = false;
          } else {
            out << ", ";
          }
          out << "{"
              << "\"name\": \"" << zone->name() << "\", "
              << "\"allocated\": " << zone_segment_bytes_allocated << ", "
              << "\"used\": " << zone_allocation_size << ", "
              << "\"freed\": " << freed_size << "}";
          total_segment_bytes_allocated += zone_segment_bytes_allocated;
          total_zone_allocation_size += zone_allocation_size;
          total_zone_freed_size += freed_size;
        }
        out << "], ";
      } else {
        // Just calculate total allocated/used memory values.
        for (const Zone* zone : active_zones_) {
          total_segment_bytes_allocated += zone->segment_bytes_allocated();
          total_zone_allocation_size += zone->allocation_size_for_tracing();
          total_zone_freed_size += zone->freed_size_for_tracing();
        }
      }
      out << "\"allocated\": " << total_segment_bytes_allocated << ", "
          << "\"used\": " << total_zone_allocation_size << ", "
          << "\"freed\": " << total_zone_freed_size << "}";
    }
  
    Isolate* const isolate_;
    std::atomic<size_t> nesting_depth_{0};
  
    base::Mutex mutex_;
    std::unordered_set<const Zone*> active_zones_;
  #ifdef V8_ENABLE_PRECISE_ZONE_STATS
    TypeStats type_stats_;
  #endif
    std::ostringstream buffer_;
    // This value is increased on both allocations and deallocations.
    size_t memory_traffic_since_last_report_ = 0;
  };
  
  #ifdef DEBUG
  std::atomic<size_t> Isolate::non_disposed_isolates_;
  #endif  // DEBUG
  
  // static
  Isolate* Isolate::New() {
    // IsolateAllocator allocates the memory for the Isolate object according to
    // the given allocation mode.
    std::unique_ptr<IsolateAllocator> isolate_allocator =
        std::make_unique<IsolateAllocator>();
    // Construct Isolate object in the allocated memory.
    void* isolate_ptr = isolate_allocator->isolate_memory();
    Isolate* isolate = new (isolate_ptr) Isolate(std::move(isolate_allocator));
  #ifdef V8_COMPRESS_POINTERS_IN_ISOLATE_CAGE
    DCHECK(IsAligned(isolate->isolate_root(), kPtrComprCageBaseAlignment));
    DCHECK_EQ(isolate->isolate_root(), isolate->cage_base());
  #endif
  
  #ifdef DEBUG
    non_disposed_isolates_++;
  #endif  // DEBUG
  
    return isolate;
  }
  
  // static
  void Isolate::Delete(Isolate* isolate) {
    DCHECK_NOT_NULL(isolate);
    // Temporarily set this isolate as current so that various parts of
    // the isolate can access it in their destructors without having a
    // direct pointer. We don't use Enter/Exit here to avoid
    // initializing the thread data.
    PerIsolateThreadData* saved_data = isolate->CurrentPerIsolateThreadData();
    DCHECK_EQ(true, isolate_key_created_.load(std::memory_order_relaxed));
    Isolate* saved_isolate = reinterpret_cast<Isolate*>(
        base::Thread::GetThreadLocal(isolate->isolate_key_));
    SetIsolateThreadLocals(isolate, nullptr);
    isolate->set_thread_id(ThreadId::Current());
  
    isolate->Deinit();
  
  #ifdef DEBUG
    non_disposed_isolates_--;
  #endif  // DEBUG
  
    // Take ownership of the IsolateAllocator to ensure the Isolate memory will
    // be available during Isolate descructor call.
    std::unique_ptr<IsolateAllocator> isolate_allocator =
        std::move(isolate->isolate_allocator_);
    isolate->~Isolate();
    // Now free the memory owned by the allocator.
    isolate_allocator.reset();
  
    // Restore the previous current isolate.
    SetIsolateThreadLocals(saved_isolate, saved_data);
  }
  
  void Isolate::SetUpFromReadOnlyArtifacts(
      std::shared_ptr<ReadOnlyArtifacts> artifacts, ReadOnlyHeap* ro_heap) {
    if (ReadOnlyHeap::IsReadOnlySpaceShared()) {
      DCHECK_NOT_NULL(artifacts);
      artifacts_ = artifacts;
    } else {
      DCHECK_NULL(artifacts);
    }
    DCHECK_NOT_NULL(ro_heap);
    DCHECK_IMPLIES(read_only_heap_ != nullptr, read_only_heap_ == ro_heap);
    read_only_heap_ = ro_heap;
    heap_.SetUpFromReadOnlyHeap(read_only_heap_);
  }
  
  v8::PageAllocator* Isolate::page_allocator() const {
    return isolate_allocator_->page_allocator();
  }
  
  Isolate::Isolate(std::unique_ptr<i::IsolateAllocator> isolate_allocator)
      : isolate_data_(this, isolate_allocator->GetPtrComprCageBase()),
        isolate_allocator_(std::move(isolate_allocator)),
        id_(isolate_counter.fetch_add(1, std::memory_order_relaxed)),
        allocator_(new TracingAccountingAllocator(this)),
        builtins_(this),
  #if defined(DEBUG) || defined(VERIFY_HEAP)
        num_active_deserializers_(0),
  #endif
        rail_mode_(PERFORMANCE_ANIMATION),
        code_event_dispatcher_(new CodeEventDispatcher()),
        persistent_handles_list_(new PersistentHandlesList()),
        jitless_(FLAG_jitless),
  #if V8_SFI_HAS_UNIQUE_ID
        next_unique_sfi_id_(0),
  #endif
        next_module_async_evaluating_ordinal_(
            SourceTextModule::kFirstAsyncEvaluatingOrdinal),
        cancelable_task_manager_(new CancelableTaskManager()) {
    TRACE_ISOLATE(constructor);
    CheckIsolateLayout();
  
    // ThreadManager is initialized early to support locking an isolate
    // before it is entered.
    thread_manager_ = new ThreadManager(this);
  
    handle_scope_data_.Initialize();
  
  #define ISOLATE_INIT_EXECUTE(type, name, initial_value) \
    name##_ = (initial_value);
    ISOLATE_INIT_LIST(ISOLATE_INIT_EXECUTE)
  #undef ISOLATE_INIT_EXECUTE
  
  #define ISOLATE_INIT_ARRAY_EXECUTE(type, name, length) \
    memset(name##_, 0, sizeof(type) * length);
    ISOLATE_INIT_ARRAY_LIST(ISOLATE_INIT_ARRAY_EXECUTE)
  #undef ISOLATE_INIT_ARRAY_EXECUTE
  
    InitializeLoggingAndCounters();
    debug_ = new Debug(this);
  
    InitializeDefaultEmbeddedBlob();
  
    MicrotaskQueue::SetUpDefaultMicrotaskQueue(this);
  }
  
  void Isolate::CheckIsolateLayout() {
    CHECK_EQ(OFFSET_OF(Isolate, isolate_data_), 0);
    CHECK_EQ(static_cast<int>(OFFSET_OF(Isolate, isolate_data_.embedder_data_)),
             Internals::kIsolateEmbedderDataOffset);
    CHECK_EQ(static_cast<int>(
                 OFFSET_OF(Isolate, isolate_data_.fast_c_call_caller_fp_)),
             Internals::kIsolateFastCCallCallerFpOffset);
    CHECK_EQ(static_cast<int>(
                 OFFSET_OF(Isolate, isolate_data_.fast_c_call_caller_pc_)),
             Internals::kIsolateFastCCallCallerPcOffset);
    CHECK_EQ(static_cast<int>(OFFSET_OF(Isolate, isolate_data_.cage_base_)),
             Internals::kIsolateCageBaseOffset);
    CHECK_EQ(static_cast<int>(
                 OFFSET_OF(Isolate, isolate_data_.long_task_stats_counter_)),
             Internals::kIsolateLongTaskStatsCounterOffset);
    CHECK_EQ(static_cast<int>(OFFSET_OF(Isolate, isolate_data_.stack_guard_)),
             Internals::kIsolateStackGuardOffset);
    CHECK_EQ(static_cast<int>(OFFSET_OF(Isolate, isolate_data_.roots_)),
             Internals::kIsolateRootsOffset);
  
  #ifdef V8_HEAP_SANDBOX
    CHECK_EQ(static_cast<int>(OFFSET_OF(ExternalPointerTable, buffer_)),
             Internals::kExternalPointerTableBufferOffset);
    CHECK_EQ(static_cast<int>(OFFSET_OF(ExternalPointerTable, length_)),
             Internals::kExternalPointerTableLengthOffset);
    CHECK_EQ(static_cast<int>(OFFSET_OF(ExternalPointerTable, capacity_)),
             Internals::kExternalPointerTableCapacityOffset);
  #endif
  }
  
  void Isolate::ClearSerializerData() {
    delete external_reference_map_;
    external_reference_map_ = nullptr;
  }
  
  bool Isolate::LogObjectRelocation() {
    return FLAG_verify_predictable || logger()->is_logging() || is_profiling() ||
           heap()->isolate()->logger()->is_listening_to_code_events() ||
           (heap_profiler() != nullptr &&
            heap_profiler()->is_tracking_object_moves()) ||
           heap()->has_heap_object_allocation_tracker();
  }
  
  void Isolate::Deinit() {
    TRACE_ISOLATE(deinit);
  
    tracing_cpu_profiler_.reset();
    if (FLAG_stress_sampling_allocation_profiler > 0) {
      heap_profiler()->StopSamplingHeapProfiler();
    }
  
    metrics_recorder_->NotifyIsolateDisposal();
    recorder_context_id_map_.clear();
  
  #if defined(V8_OS_WIN64)
    if (win64_unwindinfo::CanRegisterUnwindInfoForNonABICompliantCodeRange() &&
        heap()->memory_allocator() && RequiresCodeRange()) {
      const base::AddressRegion& code_region = heap()->code_region();
      void* start = reinterpret_cast<void*>(code_region.begin());
      win64_unwindinfo::UnregisterNonABICompliantCodeRange(start);
    }
  #endif  // V8_OS_WIN64
  
    FutexEmulation::IsolateDeinit(this);
  
    debug()->Unload();
  
  #if V8_ENABLE_WEBASSEMBLY
    wasm_engine()->DeleteCompileJobsOnIsolate(this);
  
    BackingStore::RemoveSharedWasmMemoryObjects(this);
  #endif  // V8_ENABLE_WEBASSEMBLY
  
    if (concurrent_recompilation_enabled()) {
      optimizing_compile_dispatcher_->Stop();
      delete optimizing_compile_dispatcher_;
      optimizing_compile_dispatcher_ = nullptr;
    }
  
    // All client isolates should already be detached.
    DCHECK_NULL(client_isolate_head_);
  
    // Help sweeper threads complete sweeping to stop faster.
    heap_.mark_compact_collector()->DrainSweepingWorklists();
    heap_.mark_compact_collector()->sweeper()->EnsureIterabilityCompleted();
  
    heap_.memory_allocator()->unmapper()->EnsureUnmappingCompleted();
  
    DumpAndResetStats();
  
    if (FLAG_print_deopt_stress) {
      PrintF(stdout, "=== Stress deopt counter: %u\n", stress_deopt_count_);
    }
  
    // We must stop the logger before we tear down other components.
    sampler::Sampler* sampler = logger_->sampler();
    if (sampler && sampler->IsActive()) sampler->Stop();
  
    FreeThreadResources();
    logger_->StopProfilerThread();
  
    // We start with the heap tear down so that releasing managed objects does
    // not cause a GC.
    heap_.StartTearDown();
  
    ReleaseSharedPtrs();
  
    string_table_.reset();
    builtins_.TearDown();
    bootstrapper_->TearDown();
  
    if (runtime_profiler_ != nullptr) {
      delete runtime_profiler_;
      runtime_profiler_ = nullptr;
    }
  
    delete heap_profiler_;
    heap_profiler_ = nullptr;
  
    compiler_dispatcher_->AbortAll();
    delete compiler_dispatcher_;
    compiler_dispatcher_ = nullptr;
  
    // This stops cancelable tasks (i.e. concurrent marking tasks)
    cancelable_task_manager()->CancelAndWait();
  
    main_thread_local_isolate_->heap()->FreeLinearAllocationArea();
  
    if (shared_isolate_) {
      DetachFromSharedIsolate();
    }
  
    heap_.TearDown();
  
    main_thread_local_isolate_.reset();
  
    FILE* logfile = logger_->TearDownAndGetLogFile();
    if (logfile != nullptr) base::Fclose(logfile);
  
  #if V8_ENABLE_WEBASSEMBLY
    wasm_engine_->RemoveIsolate(this);
  #endif  // V8_ENABLE_WEBASSEMBLY
  
    TearDownEmbeddedBlob();
  
    delete interpreter_;
    interpreter_ = nullptr;
  
    delete ast_string_constants_;
    ast_string_constants_ = nullptr;
  
    code_event_dispatcher_.reset();
  
    delete root_index_map_;
    root_index_map_ = nullptr;
  
    delete compiler_zone_;
    compiler_zone_ = nullptr;
    compiler_cache_ = nullptr;
  
    SetCodePages(nullptr);
  
    ClearSerializerData();
  
    {
      base::MutexGuard lock_guard(&thread_data_table_mutex_);
      thread_data_table_.RemoveAllThreads();
    }
  }
  
  void Isolate::SetIsolateThreadLocals(Isolate* isolate,
                                       PerIsolateThreadData* data) {
    base::Thread::SetThreadLocal(isolate_key_, isolate);
    base::Thread::SetThreadLocal(per_isolate_thread_data_key_, data);
  }
  
  Isolate::~Isolate() {
    TRACE_ISOLATE(destructor);
  
    // The entry stack must be empty when we get here.
    DCHECK(entry_stack_ == nullptr || entry_stack_->previous_item == nullptr);
  
    delete entry_stack_;
    entry_stack_ = nullptr;
  
    delete date_cache_;
    date_cache_ = nullptr;
  
    delete regexp_stack_;
    regexp_stack_ = nullptr;
  
    delete descriptor_lookup_cache_;
    descriptor_lookup_cache_ = nullptr;
  
    delete load_stub_cache_;
    load_stub_cache_ = nullptr;
    delete store_stub_cache_;
    store_stub_cache_ = nullptr;
  
    delete materialized_object_store_;
    materialized_object_store_ = nullptr;
  
    delete logger_;
    logger_ = nullptr;
  
    delete handle_scope_implementer_;
    handle_scope_implementer_ = nullptr;
  
    delete code_tracer();
    set_code_tracer(nullptr);
  
    delete compilation_cache_;
    compilation_cache_ = nullptr;
    delete bootstrapper_;
    bootstrapper_ = nullptr;
    delete inner_pointer_to_code_cache_;
    inner_pointer_to_code_cache_ = nullptr;
  
    delete thread_manager_;
    thread_manager_ = nullptr;
  
    bigint_processor_->Destroy();
  
    delete global_handles_;
    global_handles_ = nullptr;
    delete eternal_handles_;
    eternal_handles_ = nullptr;
  
    delete string_stream_debug_object_cache_;
    string_stream_debug_object_cache_ = nullptr;
  
    delete random_number_generator_;
    random_number_generator_ = nullptr;
  
    delete fuzzer_rng_;
    fuzzer_rng_ = nullptr;
  
    delete debug_;
    debug_ = nullptr;
  
    delete cancelable_task_manager_;
    cancelable_task_manager_ = nullptr;
  
    delete allocator_;
    allocator_ = nullptr;
  
    // Assert that |default_microtask_queue_| is the last MicrotaskQueue instance.
    DCHECK_IMPLIES(default_microtask_queue_,
                   default_microtask_queue_ == default_microtask_queue_->next());
    delete default_microtask_queue_;
    default_microtask_queue_ = nullptr;
  
    // The ReadOnlyHeap should not be destroyed when sharing without pointer
    // compression as the object itself is shared.
    if (read_only_heap_->IsOwnedByIsolate()) {
      delete read_only_heap_;
      read_only_heap_ = nullptr;
    }
  }
  
  void Isolate::InitializeThreadLocal() {
    thread_local_top()->Initialize(this);
    clear_pending_exception();
    clear_pending_message();
    clear_scheduled_exception();
  }
  
  void Isolate::SetTerminationOnExternalTryCatch() {
    if (try_catch_handler() == nullptr) return;
    try_catch_handler()->can_continue_ = false;
    try_catch_handler()->has_terminated_ = true;
    try_catch_handler()->exception_ =
        reinterpret_cast<void*>(ReadOnlyRoots(heap()).null_value().ptr());
  }
  
  bool Isolate::PropagatePendingExceptionToExternalTryCatch() {
    Object exception = pending_exception();
  
    if (IsJavaScriptHandlerOnTop(exception)) {
      thread_local_top()->external_caught_exception_ = false;
      return false;
    }
  
    if (!IsExternalHandlerOnTop(exception)) {
      thread_local_top()->external_caught_exception_ = false;
      return true;
    }
  
    thread_local_top()->external_caught_exception_ = true;
    if (!is_catchable_by_javascript(exception)) {
      SetTerminationOnExternalTryCatch();
    } else {
      v8::TryCatch* handler = try_catch_handler();
      DCHECK(thread_local_top()->pending_message_obj_.IsJSMessageObject() ||
             thread_local_top()->pending_message_obj_.IsTheHole(this));
      handler->can_continue_ = true;
      handler->has_terminated_ = false;
      handler->exception_ = reinterpret_cast<void*>(pending_exception().ptr());
      // Propagate to the external try-catch only if we got an actual message.
      if (thread_local_top()->pending_message_obj_.IsTheHole(this)) return true;
  
      handler->message_obj_ =
          reinterpret_cast<void*>(thread_local_top()->pending_message_obj_.ptr());
    }
    return true;
  }
  
  bool Isolate::InitializeCounters() {
    if (async_counters_) return false;
    async_counters_ = std::make_shared<Counters>(this);
    return true;
  }
  
  void Isolate::InitializeLoggingAndCounters() {
    if (logger_ == nullptr) {
      logger_ = new Logger(this);
    }
    InitializeCounters();
  }
  
  namespace {
  
  void CreateOffHeapTrampolines(Isolate* isolate) {
    DCHECK_NOT_NULL(isolate->embedded_blob_code());
    DCHECK_NE(0, isolate->embedded_blob_code_size());
    DCHECK_NOT_NULL(isolate->embedded_blob_data());
    DCHECK_NE(0, isolate->embedded_blob_data_size());
  
    HandleScope scope(isolate);
    Builtins* builtins = isolate->builtins();
  
    EmbeddedData d = EmbeddedData::FromBlob(isolate);
  
    STATIC_ASSERT(Builtins::kAllBuiltinsAreIsolateIndependent);
    for (int i = 0; i < Builtins::builtin_count; i++) {
      Address instruction_start = d.InstructionStartOfBuiltin(i);
      Handle<Code> trampoline = isolate->factory()->NewOffHeapTrampolineFor(
          builtins->builtin_handle(i), instruction_start);
  
      // From this point onwards, the old builtin code object is unreachable and
      // will be collected by the next GC.
      builtins->set_builtin(i, *trampoline);
    }
  }
  
  #ifdef DEBUG
  bool IsolateIsCompatibleWithEmbeddedBlob(Isolate* isolate) {
    EmbeddedData d = EmbeddedData::FromBlob(isolate);
    return (d.IsolateHash() == isolate->HashIsolateForEmbeddedBlob());
  }
  #endif  // DEBUG
  
  }  // namespace
  
  void Isolate::InitializeDefaultEmbeddedBlob() {
    const uint8_t* code = DefaultEmbeddedBlobCode();
    uint32_t code_size = DefaultEmbeddedBlobCodeSize();
    const uint8_t* data = DefaultEmbeddedBlobData();
    uint32_t data_size = DefaultEmbeddedBlobDataSize();
  
  #ifdef V8_MULTI_SNAPSHOTS
    if (!FLAG_untrusted_code_mitigations) {
      code = TrustedEmbeddedBlobCode();
      code_size = TrustedEmbeddedBlobCodeSize();
      data = TrustedEmbeddedBlobData();
      data_size = TrustedEmbeddedBlobDataSize();
    }
  #endif
  
    if (StickyEmbeddedBlobCode() != nullptr) {
      base::MutexGuard guard(current_embedded_blob_refcount_mutex_.Pointer());
      // Check again now that we hold the lock.
      if (StickyEmbeddedBlobCode() != nullptr) {
        code = StickyEmbeddedBlobCode();
        code_size = StickyEmbeddedBlobCodeSize();
        data = StickyEmbeddedBlobData();
        data_size = StickyEmbeddedBlobDataSize();
        current_embedded_blob_refs_++;
      }
    }
  
    if (code == nullptr) {
      CHECK_EQ(0, code_size);
    } else {
      SetEmbeddedBlob(code, code_size, data, data_size);
    }
  }
  
  void Isolate::CreateAndSetEmbeddedBlob() {
    base::MutexGuard guard(current_embedded_blob_refcount_mutex_.Pointer());
  
    PrepareBuiltinSourcePositionMap();
  
    PrepareBuiltinLabelInfoMap();
  
    // If a sticky blob has been set, we reuse it.
    if (StickyEmbeddedBlobCode() != nullptr) {
      CHECK_EQ(embedded_blob_code(), StickyEmbeddedBlobCode());
      CHECK_EQ(embedded_blob_data(), StickyEmbeddedBlobData());
      CHECK_EQ(CurrentEmbeddedBlobCode(), StickyEmbeddedBlobCode());
      CHECK_EQ(CurrentEmbeddedBlobData(), StickyEmbeddedBlobData());
    } else {
      // Create and set a new embedded blob.
      uint8_t* code;
      uint32_t code_size;
      uint8_t* data;
      uint32_t data_size;
      InstructionStream::CreateOffHeapInstructionStream(this, &code, &code_size,
                                                        &data, &data_size);
  
      CHECK_EQ(0, current_embedded_blob_refs_);
      const uint8_t* const_code = const_cast<const uint8_t*>(code);
      const uint8_t* const_data = const_cast<const uint8_t*>(data);
      SetEmbeddedBlob(const_code, code_size, const_data, data_size);
      current_embedded_blob_refs_++;
  
      SetStickyEmbeddedBlob(code, code_size, data, data_size);
    }
  
    MaybeRemapEmbeddedBuiltinsIntoCodeRange();
  
    CreateOffHeapTrampolines(this);
  }
  
  void Isolate::MaybeRemapEmbeddedBuiltinsIntoCodeRange() {
    if (!is_short_builtin_calls_enabled() || !RequiresCodeRange()) return;
  
    CHECK_NOT_NULL(embedded_blob_code_);
    CHECK_NE(embedded_blob_code_size_, 0);
  
    DCHECK_NOT_NULL(heap_.code_range_);
    embedded_blob_code_ = heap_.code_range_->RemapEmbeddedBuiltins(
        this, embedded_blob_code_, embedded_blob_code_size_);
    CHECK_NOT_NULL(embedded_blob_code_);
    // The un-embedded code blob is already a part of the registered code range
    // so it's not necessary to register it again.
  }
  
  void Isolate::TearDownEmbeddedBlob() {
    // Nothing to do in case the blob is embedded into the binary or unset.
    if (StickyEmbeddedBlobCode() == nullptr) return;
  
    if (!is_short_builtin_calls_enabled()) {
      CHECK_EQ(embedded_blob_code(), StickyEmbeddedBlobCode());
      CHECK_EQ(embedded_blob_data(), StickyEmbeddedBlobData());
    }
    CHECK_EQ(CurrentEmbeddedBlobCode(), StickyEmbeddedBlobCode());
    CHECK_EQ(CurrentEmbeddedBlobData(), StickyEmbeddedBlobData());
  
    base::MutexGuard guard(current_embedded_blob_refcount_mutex_.Pointer());
    current_embedded_blob_refs_--;
    if (current_embedded_blob_refs_ == 0 && enable_embedded_blob_refcounting_) {
      // We own the embedded blob and are the last holder. Free it.
      InstructionStream::FreeOffHeapInstructionStream(
          const_cast<uint8_t*>(CurrentEmbeddedBlobCode()),
          embedded_blob_code_size(),
          const_cast<uint8_t*>(CurrentEmbeddedBlobData()),
          embedded_blob_data_size());
      ClearEmbeddedBlob();
    }
  }
  
  bool Isolate::InitWithoutSnapshot() { return Init(nullptr, nullptr, false); }
  
  bool Isolate::InitWithSnapshot(SnapshotData* startup_snapshot_data,
                                 SnapshotData* read_only_snapshot_data,
                                 bool can_rehash) {
    DCHECK_NOT_NULL(startup_snapshot_data);
    DCHECK_NOT_NULL(read_only_snapshot_data);
    return Init(startup_snapshot_data, read_only_snapshot_data, can_rehash);
  }
  
  static std::string AddressToString(uintptr_t address) {
    std::stringstream stream_address;
    stream_address << "0x" << std::hex << address;
    return stream_address.str();
  }
  
  void Isolate::AddCrashKeysForIsolateAndHeapPointers() {
    DCHECK_NOT_NULL(add_crash_key_callback_);
  
    const uintptr_t isolate_address = reinterpret_cast<uintptr_t>(this);
    add_crash_key_callback_(v8::CrashKeyId::kIsolateAddress,
                            AddressToString(isolate_address));
  
    const uintptr_t ro_space_firstpage_address =
        heap()->read_only_space()->FirstPageAddress();
    add_crash_key_callback_(v8::CrashKeyId::kReadonlySpaceFirstPageAddress,
                            AddressToString(ro_space_firstpage_address));
    const uintptr_t map_space_firstpage_address =
        heap()->map_space()->FirstPageAddress();
    add_crash_key_callback_(v8::CrashKeyId::kMapSpaceFirstPageAddress,
                            AddressToString(map_space_firstpage_address));
    const uintptr_t code_space_firstpage_address =
        heap()->code_space()->FirstPageAddress();
    add_crash_key_callback_(v8::CrashKeyId::kCodeSpaceFirstPageAddress,
                            AddressToString(code_space_firstpage_address));
  }
  
  void Isolate::InitializeCodeRanges() {
    DCHECK_NULL(GetCodePages());
    MemoryRange embedded_range{
        reinterpret_cast<const void*>(embedded_blob_code()),
        embedded_blob_code_size()};
    code_pages_buffer1_.push_back(embedded_range);
    SetCodePages(&code_pages_buffer1_);
  }
  
  namespace {
  
  // This global counter contains number of stack loads/stores per optimized/wasm
  // function.
  using MapOfLoadsAndStoresPerFunction =
      std::map<std::string /* function_name */,
               std::pair<uint64_t /* loads */, uint64_t /* stores */>>;
  MapOfLoadsAndStoresPerFunction* stack_access_count_map = nullptr;
  
  class BigIntPlatform : public bigint::Platform {
   public:
    explicit BigIntPlatform(Isolate* isolate) : isolate_(isolate) {}
    ~BigIntPlatform() override = default;
  
    bool InterruptRequested() override {
      StackLimitCheck interrupt_check(isolate_);
      return (interrupt_check.InterruptRequested() &&
              isolate_->stack_guard()->HasTerminationRequest());
    }
  
   private:
    Isolate* isolate_;
  };
  }  // namespace
  
  bool Isolate::Init(SnapshotData* startup_snapshot_data,
                     SnapshotData* read_only_snapshot_data, bool can_rehash) {
    TRACE_ISOLATE(init);
    const bool create_heap_objects = (read_only_snapshot_data == nullptr);
    // We either have both or neither.
    DCHECK_EQ(create_heap_objects, startup_snapshot_data == nullptr);
  
    base::ElapsedTimer timer;
    if (create_heap_objects && FLAG_profile_deserialization) timer.Start();
  
    time_millis_at_init_ = heap_.MonotonicallyIncreasingTimeInMs();
  
    stress_deopt_count_ = FLAG_deopt_every_n_times;
    force_slow_path_ = FLAG_force_slow_path;
  
    has_fatal_error_ = false;
  
    // The initialization process does not handle memory exhaustion.
    AlwaysAllocateScope always_allocate(heap());
  
  #define ASSIGN_ELEMENT(CamelName, hacker_name)                  \
    isolate_addresses_[IsolateAddressId::k##CamelName##Address] = \
        reinterpret_cast<Address>(hacker_name##_address());
    FOR_EACH_ISOLATE_ADDRESS_NAME(ASSIGN_ELEMENT)
  #undef ASSIGN_ELEMENT
  
    // We need to initialize code_pages_ before any on-heap code is allocated to
    // make sure we record all code allocations.
    InitializeCodeRanges();
  
    compilation_cache_ = new CompilationCache(this);
    descriptor_lookup_cache_ = new DescriptorLookupCache();
    inner_pointer_to_code_cache_ = new InnerPointerToCodeCache(this);
    global_handles_ = new GlobalHandles(this);
    eternal_handles_ = new EternalHandles();
    bootstrapper_ = new Bootstrapper(this);
    handle_scope_implementer_ = new HandleScopeImplementer(this);
    load_stub_cache_ = new StubCache(this);
    store_stub_cache_ = new StubCache(this);
    materialized_object_store_ = new MaterializedObjectStore(this);
    regexp_stack_ = new RegExpStack();
    regexp_stack_->isolate_ = this;
    date_cache_ = new DateCache();
    heap_profiler_ = new HeapProfiler(heap());
    interpreter_ = new interpreter::Interpreter(this);
    string_table_.reset(new StringTable(this));
    bigint_processor_ = bigint::Processor::New(new BigIntPlatform(this));
  
    compiler_dispatcher_ =
        new CompilerDispatcher(this, V8::GetCurrentPlatform(), FLAG_stack_size);
  
    // Enable logging before setting up the heap
    logger_->SetUp(this);
  
    metrics_recorder_ = std::make_shared<metrics::Recorder>();
  
    {
      // Ensure that the thread has a valid stack guard.  The v8::Locker object
      // will ensure this too, but we don't have to use lockers if we are only
      // using one thread.
      ExecutionAccess lock(this);
      stack_guard()->InitThread(lock);
    }
  
    // SetUp the object heap.
    DCHECK(!heap_.HasBeenSetUp());
    heap_.SetUp();
    ReadOnlyHeap::SetUp(this, read_only_snapshot_data, can_rehash);
    heap_.SetUpSpaces();
  
    if (V8_SHORT_BUILTIN_CALLS_BOOL && FLAG_short_builtin_calls) {
      // Check if the system has more than 4GB of physical memory by comparing the
      // old space size with respective threshold value.
      //
      // Additionally, enable if there is already a process-wide CodeRange that
      // has re-embedded builtins.
      is_short_builtin_calls_enabled_ = (heap_.MaxOldGenerationSize() >=
                                         kShortBuiltinCallsOldSpaceSizeThreshold);
      if (COMPRESS_POINTERS_IN_SHARED_CAGE_BOOL) {
        std::shared_ptr<CodeRange> code_range =
            CodeRange::GetProcessWideCodeRange();
        if (code_range && code_range->embedded_blob_code_copy() != nullptr) {
          is_short_builtin_calls_enabled_ = true;
        }
      }
    }
  
    // Create LocalIsolate/LocalHeap for the main thread and set state to Running.
    main_thread_local_isolate_.reset(new LocalIsolate(this, ThreadKind::kMain));
    main_thread_local_heap()->Unpark();
  
    heap_.InitializeMainThreadLocalHeap(main_thread_local_heap());
  
    isolate_data_.external_reference_table()->Init(this);
  
  #if V8_ENABLE_WEBASSEMBLY
    SetWasmEngine(wasm::WasmEngine::GetWasmEngine());
  #endif  // V8_ENABLE_WEBASSEMBLY
  
    if (setup_delegate_ == nullptr) {
      setup_delegate_ = new SetupIsolateDelegate(create_heap_objects);
    }
  
    if (!FLAG_inline_new) heap_.DisableInlineAllocation();
  
    if (!setup_delegate_->SetupHeap(&heap_)) {
      V8::FatalProcessOutOfMemory(this, "heap object creation");
      return false;
    }
  
    if (create_heap_objects) {
      // Terminate the startup object cache so we can iterate.
      startup_object_cache_.push_back(ReadOnlyRoots(this).undefined_value());
    }
  
    InitializeThreadLocal();
  
    // Profiler has to be created after ThreadLocal is initialized
    // because it makes use of interrupts.
    tracing_cpu_profiler_.reset(new TracingCpuProfilerImpl(this));
  
    bootstrapper_->Initialize(create_heap_objects);
  
    if (create_heap_objects) {
      builtins_constants_table_builder_ = new BuiltinsConstantsTableBuilder(this);
  
      setup_delegate_->SetupBuiltins(this);
  
  #ifndef V8_TARGET_ARCH_ARM
      // Store the interpreter entry trampoline on the root list. It is used as a
      // template for further copies that may later be created to help profile
      // interpreted code.
      // We currently cannot do this on arm due to RELATIVE_CODE_TARGETs
      // assuming that all possible Code targets may be addressed with an int24
      // offset, effectively limiting code space size to 32MB. We can guarantee
      // this at mksnapshot-time, but not at runtime.
      // See also: https://crbug.com/v8/8713.
      heap_.SetInterpreterEntryTrampolineForProfiling(
          heap_.builtin(Builtins::kInterpreterEntryTrampoline));
  #endif
  
      builtins_constants_table_builder_->Finalize();
      delete builtins_constants_table_builder_;
      builtins_constants_table_builder_ = nullptr;
  
      CreateAndSetEmbeddedBlob();
    } else {
      setup_delegate_->SetupBuiltins(this);
      MaybeRemapEmbeddedBuiltinsIntoCodeRange();
    }
  
    // Initialize custom memcopy and memmove functions (must happen after
    // embedded blob setup).
    init_memcopy_functions();
  
    if (FLAG_log_internal_timer_events) {
      set_event_logger(Logger::DefaultEventLoggerSentinel);
    }
  
    if (FLAG_trace_turbo || FLAG_trace_turbo_graph || FLAG_turbo_profiling) {
      PrintF("Concurrent recompilation has been disabled for tracing.\n");
    } else if (OptimizingCompileDispatcher::Enabled()) {
      optimizing_compile_dispatcher_ = new OptimizingCompileDispatcher(this);
    }
  
    // Initialize runtime profiler before deserialization, because collections may
    // occur, clearing/updating ICs.
    runtime_profiler_ = new RuntimeProfiler(this);
  
    // If we are deserializing, read the state into the now-empty heap.
    {
      AlwaysAllocateScope always_allocate(heap());
      CodeSpaceMemoryModificationScope modification_scope(heap());
  
      if (create_heap_objects) {
        heap_.read_only_space()->ClearStringPaddingIfNeeded();
        read_only_heap_->OnCreateHeapObjectsComplete(this);
      } else {
        StartupDeserializer startup_deserializer(this, startup_snapshot_data,
                                                 can_rehash);
        startup_deserializer.DeserializeIntoIsolate();
      }
      load_stub_cache_->Initialize();
      store_stub_cache_->Initialize();
      interpreter_->Initialize();
      heap_.NotifyDeserializationComplete();
    }
  
  #ifdef VERIFY_HEAP
    if (FLAG_verify_heap) {
      heap_.VerifyReadOnlyHeap();
    }
  #endif
  
    delete setup_delegate_;
    setup_delegate_ = nullptr;
  
    Builtins::InitializeBuiltinEntryTable(this);
    Builtins::EmitCodeCreateEvents(this);
  
  #ifdef DEBUG
    // Verify that the current heap state (usually deserialized from the snapshot)
    // is compatible with the embedded blob. If this DCHECK fails, we've likely
    // loaded a snapshot generated by a different V8 version or build-time
    // configuration.
    if (!IsolateIsCompatibleWithEmbeddedBlob(this)) {
      FATAL(
          "The Isolate is incompatible with the embedded blob. This is usually "
          "caused by incorrect usage of mksnapshot. When generating custom "
          "snapshots, embedders must ensure they pass the same flags as during "
          "the V8 build process (e.g.: --turbo-instruction-scheduling).");
    }
  #endif  // DEBUG
  
  #ifndef V8_TARGET_ARCH_ARM
    // The IET for profiling should always be a full on-heap Code object.
    DCHECK(!Code::cast(heap_.interpreter_entry_trampoline_for_profiling())
                .is_off_heap_trampoline());
  #endif  // V8_TARGET_ARCH_ARM
  
    if (FLAG_print_builtin_code) builtins()->PrintBuiltinCode();
    if (FLAG_print_builtin_size) builtins()->PrintBuiltinSize();
  
    // Finish initialization of ThreadLocal after deserialization is done.
    clear_pending_exception();
    clear_pending_message();
    clear_scheduled_exception();
  
    // Quiet the heap NaN if needed on target platform.
    if (!create_heap_objects)
      Assembler::QuietNaN(ReadOnlyRoots(this).nan_value());
  
    if (FLAG_trace_turbo) {
      // Create an empty file.
      std::ofstream(GetTurboCfgFileName(this).c_str(), std::ios_base::trunc);
    }
  
    {
      HandleScope scope(this);
      ast_string_constants_ = new AstStringConstants(this, HashSeed(this));
    }
  
    initialized_from_snapshot_ = !create_heap_objects;
  
    if (FLAG_stress_sampling_allocation_profiler > 0) {
      uint64_t sample_interval = FLAG_stress_sampling_allocation_profiler;
      int stack_depth = 128;
      v8::HeapProfiler::SamplingFlags sampling_flags =
          v8::HeapProfiler::SamplingFlags::kSamplingForceGC;
      heap_profiler()->StartSamplingHeapProfiler(sample_interval, stack_depth,
                                                 sampling_flags);
    }
  
  #if defined(V8_OS_WIN64)
    if (win64_unwindinfo::CanRegisterUnwindInfoForNonABICompliantCodeRange()) {
      const base::AddressRegion& code_region = heap()->code_region();
      void* start = reinterpret_cast<void*>(code_region.begin());
      size_t size_in_bytes = code_region.size();
      win64_unwindinfo::RegisterNonABICompliantCodeRange(start, size_in_bytes);
    }
  #endif  // V8_OS_WIN64
  
    if (create_heap_objects && FLAG_profile_deserialization) {
      double ms = timer.Elapsed().InMillisecondsF();
      PrintF("[Initializing isolate from scratch took %0.3f ms]\n", ms);
    }
  
    return true;
  }
  
  void Isolate::Enter() {
    Isolate* current_isolate = nullptr;
    PerIsolateThreadData* current_data = CurrentPerIsolateThreadData();
    if (current_data != nullptr) {
      current_isolate = current_data->isolate_;
      DCHECK_NOT_NULL(current_isolate);
      if (current_isolate == this) {
        DCHECK(Current() == this);
        DCHECK_NOT_NULL(entry_stack_);
        DCHECK(entry_stack_->previous_thread_data == nullptr ||
               entry_stack_->previous_thread_data->thread_id() ==
                   ThreadId::Current());
        // Same thread re-enters the isolate, no need to re-init anything.
        entry_stack_->entry_count++;
        return;
      }
    }
  
    PerIsolateThreadData* data = FindOrAllocatePerThreadDataForThisThread();
    DCHECK_NOT_NULL(data);
    DCHECK(data->isolate_ == this);
  
    EntryStackItem* item =
        new EntryStackItem(current_data, current_isolate, entry_stack_);
    entry_stack_ = item;
  
    SetIsolateThreadLocals(this, data);
  
    // In case it's the first time some thread enters the isolate.
    set_thread_id(data->thread_id());
  }
  
  void Isolate::Exit() {
    DCHECK_NOT_NULL(entry_stack_);
    DCHECK(entry_stack_->previous_thread_data == nullptr ||
           entry_stack_->previous_thread_data->thread_id() ==
               ThreadId::Current());
  
    if (--entry_stack_->entry_count > 0) return;
  
    DCHECK_NOT_NULL(CurrentPerIsolateThreadData());
    DCHECK(CurrentPerIsolateThreadData()->isolate_ == this);
  
    // Pop the stack.
    EntryStackItem* item = entry_stack_;
    entry_stack_ = item->previous_item;
  
    PerIsolateThreadData* previous_thread_data = item->previous_thread_data;
    Isolate* previous_isolate = item->previous_isolate;
  
    delete item;
  
    // Reinit the current thread for the isolate it was running before this one.
    SetIsolateThreadLocals(previous_isolate, previous_thread_data);
  }
  
  std::unique_ptr<PersistentHandles> Isolate::NewPersistentHandles() {
    return std::make_unique<PersistentHandles>(this);
  }
  
  void Isolate::DumpAndResetStats() {
    if (FLAG_trace_turbo_stack_accesses) {
      StdoutStream os;
      uint64_t total_loads = 0;
      uint64_t total_stores = 0;
      os << "=== Stack access counters === " << std::endl;
      if (!stack_access_count_map) {
        os << "No stack accesses in optimized/wasm functions found.";
      } else {
        DCHECK_NOT_NULL(stack_access_count_map);
        os << "Number of optimized/wasm stack-access functions: "
           << stack_access_count_map->size() << std::endl;
        for (auto it = stack_access_count_map->cbegin();
             it != stack_access_count_map->cend(); it++) {
          std::string function_name((*it).first);
          std::pair<uint64_t, uint64_t> per_func_count = (*it).second;
          os << "Name: " << function_name << ", Loads: " << per_func_count.first
             << ", Stores: " << per_func_count.second << std::endl;
          total_loads += per_func_count.first;
          total_stores += per_func_count.second;
        }
        os << "Total Loads: " << total_loads << ", Total Stores: " << total_stores
           << std::endl;
        stack_access_count_map = nullptr;
      }
    }
    if (turbo_statistics() != nullptr) {
      DCHECK(FLAG_turbo_stats || FLAG_turbo_stats_nvp);
      StdoutStream os;
      if (FLAG_turbo_stats) {
        AsPrintableStatistics ps = {*turbo_statistics(), false};
        os << ps << std::endl;
      }
      if (FLAG_turbo_stats_nvp) {
        AsPrintableStatistics ps = {*turbo_statistics(), true};
        os << ps << std::endl;
      }
      delete turbo_statistics_;
      turbo_statistics_ = nullptr;
    }
  #if V8_ENABLE_WEBASSEMBLY
    // TODO(7424): There is no public API for the {WasmEngine} yet. So for now we
    // just dump and reset the engines statistics together with the Isolate.
    if (FLAG_turbo_stats_wasm) {
      wasm_engine()->DumpAndResetTurboStatistics();
    }
  #endif  // V8_ENABLE_WEBASSEMBLY
  #if V8_RUNTIME_CALL_STATS
    if (V8_UNLIKELY(TracingFlags::runtime_stats.load(std::memory_order_relaxed) ==
                    v8::tracing::TracingCategoryObserver::ENABLED_BY_NATIVE)) {
      counters()->worker_thread_runtime_call_stats()->AddToMainTable(
          counters()->runtime_call_stats());
      counters()->runtime_call_stats()->Print();
      counters()->runtime_call_stats()->Reset();
    }
  #endif  // V8_RUNTIME_CALL_STATS
    if (BasicBlockProfiler::Get()->HasData(this)) {
      StdoutStream out;
      BasicBlockProfiler::Get()->Print(out, this);
      BasicBlockProfiler::Get()->ResetCounts(this);
    }
  }
  
  void Isolate::AbortConcurrentOptimization(BlockingBehavior behavior) {
    if (concurrent_recompilation_enabled()) {
      DisallowGarbageCollection no_recursive_gc;
      optimizing_compile_dispatcher()->Flush(behavior);
    }
  }
  
  CompilationStatistics* Isolate::GetTurboStatistics() {
    if (turbo_statistics() == nullptr)
      set_turbo_statistics(new CompilationStatistics());
    return turbo_statistics();
  }
  
  CodeTracer* Isolate::GetCodeTracer() {
    if (code_tracer() == nullptr) set_code_tracer(new CodeTracer(id()));
    return code_tracer();
  }
  
  bool Isolate::use_optimizer() {
    return FLAG_opt && !serializer_enabled_ && CpuFeatures::SupportsOptimizer() &&
           !is_precise_count_code_coverage();
  }
  
  void Isolate::IncreaseTotalRegexpCodeGenerated(Handle<HeapObject> code) {
    DCHECK(code->IsCode() || code->IsByteArray());
    total_regexp_code_generated_ += code->Size();
  }
  
  bool Isolate::NeedsDetailedOptimizedCodeLineInfo() const {
    return NeedsSourcePositionsForProfiling() ||
           detailed_source_positions_for_profiling();
  }
  
  bool Isolate::NeedsSourcePositionsForProfiling() const {
    return FLAG_trace_deopt || FLAG_trace_turbo || FLAG_trace_turbo_graph ||
           FLAG_turbo_profiling || FLAG_perf_prof || is_profiling() ||
           debug_->is_active() || logger_->is_logging() || FLAG_log_maps ||
           FLAG_log_ic;
  }
  
  void Isolate::SetFeedbackVectorsForProfilingTools(Object value) {
    DCHECK(value.IsUndefined(this) || value.IsArrayList());
    heap()->set_feedback_vectors_for_profiling_tools(value);
  }
  
  void Isolate::MaybeInitializeVectorListFromHeap() {
    if (!heap()->feedback_vectors_for_profiling_tools().IsUndefined(this)) {
      // Already initialized, return early.
      DCHECK(heap()->feedback_vectors_for_profiling_tools().IsArrayList());
      return;
    }
  
    // Collect existing feedback vectors.
    std::vector<Handle<FeedbackVector>> vectors;
  
    {
      HeapObjectIterator heap_iterator(heap());
      for (HeapObject current_obj = heap_iterator.Next(); !current_obj.is_null();
           current_obj = heap_iterator.Next()) {
        if (!current_obj.IsFeedbackVector()) continue;
  
        FeedbackVector vector = FeedbackVector::cast(current_obj);
        SharedFunctionInfo shared = vector.shared_function_info();
  
        // No need to preserve the feedback vector for non-user-visible functions.
        if (!shared.IsSubjectToDebugging()) continue;
  
        vectors.emplace_back(vector, this);
      }
    }
  
    // Add collected feedback vectors to the root list lest we lose them to GC.
    Handle<ArrayList> list =
        ArrayList::New(this, static_cast<int>(vectors.size()));
    for (const auto& vector : vectors) list = ArrayList::Add(this, list, vector);
    SetFeedbackVectorsForProfilingTools(*list);
  }
  
  void Isolate::set_date_cache(DateCache* date_cache) {
    if (date_cache != date_cache_) {
      delete date_cache_;
    }
    date_cache_ = date_cache;
  }
  
  Isolate::KnownPrototype Isolate::IsArrayOrObjectOrStringPrototype(
      Object object) {
    Object context = heap()->native_contexts_list();
    while (!context.IsUndefined(this)) {
      Context current_context = Context::cast(context);
      if (current_context.initial_object_prototype() == object) {
        return KnownPrototype::kObject;
      } else if (current_context.initial_array_prototype() == object) {
        return KnownPrototype::kArray;
      } else if (current_context.initial_string_prototype() == object) {
        return KnownPrototype::kString;
      }
      context = current_context.next_context_link();
    }
    return KnownPrototype::kNone;
  }
  
  bool Isolate::IsInAnyContext(Object object, uint32_t index) {
    DisallowGarbageCollection no_gc;
    Object context = heap()->native_contexts_list();
    while (!context.IsUndefined(this)) {
      Context current_context = Context::cast(context);
      if (current_context.get(index) == object) {
        return true;
      }
      context = current_context.next_context_link();
    }
    return false;
  }
  
  void Isolate::UpdateNoElementsProtectorOnSetElement(Handle<JSObject> object) {
    DisallowGarbageCollection no_gc;
    if (!object->map().is_prototype_map()) return;
    if (!Protectors::IsNoElementsIntact(this)) return;
    KnownPrototype obj_type = IsArrayOrObjectOrStringPrototype(*object);
    if (obj_type == KnownPrototype::kNone) return;
    if (obj_type == KnownPrototype::kObject) {
      this->CountUsage(v8::Isolate::kObjectPrototypeHasElements);
    } else if (obj_type == KnownPrototype::kArray) {
      this->CountUsage(v8::Isolate::kArrayPrototypeHasElements);
    }
    Protectors::InvalidateNoElements(this);
  }
  
  static base::RandomNumberGenerator* ensure_rng_exists(
      base::RandomNumberGenerator** rng, int seed) {
    if (*rng == nullptr) {
      if (seed != 0) {
        *rng = new base::RandomNumberGenerator(seed);
      } else {
        *rng = new base::RandomNumberGenerator();
      }
    }
    return *rng;
  }
  
  base::RandomNumberGenerator* Isolate::random_number_generator() {
    // TODO(bmeurer) Initialized lazily because it depends on flags; can
    // be fixed once the default isolate cleanup is done.
    return ensure_rng_exists(&random_number_generator_, FLAG_random_seed);
  }
  
  base::RandomNumberGenerator* Isolate::fuzzer_rng() {
    if (fuzzer_rng_ == nullptr) {
      int64_t seed = FLAG_fuzzer_random_seed;
      if (seed == 0) {
        seed = random_number_generator()->initial_seed();
      }
  
      fuzzer_rng_ = new base::RandomNumberGenerator(seed);
    }
  
    return fuzzer_rng_;
  }
  
  int Isolate::GenerateIdentityHash(uint32_t mask) {
    int hash;
    int attempts = 0;
    do {
      hash = random_number_generator()->NextInt() & mask;
    } while (hash == 0 && attempts++ < 30);
    return hash != 0 ? hash : 1;
  }
  
  Code Isolate::FindCodeObject(Address a) {
    return heap()->GcSafeFindCodeForInnerPointer(a);
  }
  
  #ifdef DEBUG
  #define ISOLATE_FIELD_OFFSET(type, name, ignored) \
    const intptr_t Isolate::name##_debug_offset_ = OFFSET_OF(Isolate, name##_);
  ISOLATE_INIT_LIST(ISOLATE_FIELD_OFFSET)
  ISOLATE_INIT_ARRAY_LIST(ISOLATE_FIELD_OFFSET)
  #undef ISOLATE_FIELD_OFFSET
  #endif
  
  Handle<Symbol> Isolate::SymbolFor(RootIndex dictionary_index,
                                    Handle<String> name, bool private_symbol) {
    Handle<String> key = factory()->InternalizeString(name);
    Handle<NameDictionary> dictionary =
        Handle<NameDictionary>::cast(root_handle(dictionary_index));
    InternalIndex entry = dictionary->FindEntry(this, key);
    Handle<Symbol> symbol;
    if (entry.is_not_found()) {
      symbol =
          private_symbol ? factory()->NewPrivateSymbol() : factory()->NewSymbol();
      symbol->set_description(*key);
      dictionary = NameDictionary::Add(this, dictionary, key, symbol,
                                       PropertyDetails::Empty(), &entry);
      switch (dictionary_index) {
        case RootIndex::kPublicSymbolTable:
          symbol->set_is_in_public_symbol_table(true);
          heap()->set_public_symbol_table(*dictionary);
          break;
        case RootIndex::kApiSymbolTable:
          heap()->set_api_symbol_table(*dictionary);
          break;
        case RootIndex::kApiPrivateSymbolTable:
          heap()->set_api_private_symbol_table(*dictionary);
          break;
        default:
          UNREACHABLE();
      }
    } else {
      symbol = Handle<Symbol>(Symbol::cast(dictionary->ValueAt(entry)), this);
    }
    return symbol;
  }
  
  void Isolate::AddBeforeCallEnteredCallback(BeforeCallEnteredCallback callback) {
    auto pos = std::find(before_call_entered_callbacks_.begin(),
                         before_call_entered_callbacks_.end(), callback);
    if (pos != before_call_entered_callbacks_.end()) return;
    before_call_entered_callbacks_.push_back(callback);
  }
  
  void Isolate::RemoveBeforeCallEnteredCallback(
      BeforeCallEnteredCallback callback) {
    auto pos = std::find(before_call_entered_callbacks_.begin(),
                         before_call_entered_callbacks_.end(), callback);
    if (pos == before_call_entered_callbacks_.end()) return;
    before_call_entered_callbacks_.erase(pos);
  }
  
  void Isolate::AddCallCompletedCallback(CallCompletedCallback callback) {
    auto pos = std::find(call_completed_callbacks_.begin(),
                         call_completed_callbacks_.end(), callback);
    if (pos != call_completed_callbacks_.end()) return;
    call_completed_callbacks_.push_back(callback);
  }
  
  void Isolate::RemoveCallCompletedCallback(CallCompletedCallback callback) {
    auto pos = std::find(call_completed_callbacks_.begin(),
                         call_completed_callbacks_.end(), callback);
    if (pos == call_completed_callbacks_.end()) return;
    call_completed_callbacks_.erase(pos);
  }
  
  void Isolate::FireCallCompletedCallback(MicrotaskQueue* microtask_queue) {
    if (!thread_local_top()->CallDepthIsZero()) return;
  
    bool perform_checkpoint =
        microtask_queue &&
        microtask_queue->microtasks_policy() == v8::MicrotasksPolicy::kAuto;
  
    v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(this);
    if (perform_checkpoint) microtask_queue->PerformCheckpoint(isolate);
  
    if (call_completed_callbacks_.empty()) return;
    // Fire callbacks.  Increase call depth to prevent recursive callbacks.
    v8::Isolate::SuppressMicrotaskExecutionScope suppress(isolate);
    std::vector<CallCompletedCallback> callbacks(call_completed_callbacks_);
    for (auto& callback : callbacks) {
      callback(reinterpret_cast<v8::Isolate*>(this));
    }
  }
  
  void Isolate::UpdatePromiseHookProtector() {
    if (Protectors::IsPromiseHookIntact(this)) {
      HandleScope scope(this);
      Protectors::InvalidatePromiseHook(this);
    }
  }
  
  void Isolate::PromiseHookStateUpdated() {
    promise_hook_flags_ =
      (promise_hook_flags_ & PromiseHookFields::HasContextPromiseHook::kMask) |
      PromiseHookFields::HasIsolatePromiseHook::encode(promise_hook_) |
      PromiseHookFields::HasAsyncEventDelegate::encode(async_event_delegate_) |
      PromiseHookFields::IsDebugActive::encode(debug()->is_active());
  
    if (promise_hook_flags_ != 0) {
      UpdatePromiseHookProtector();
    }
  }
  
  namespace {
  
  MaybeHandle<JSPromise> NewRejectedPromise(Isolate* isolate,
                                            v8::Local<v8::Context> api_context,
                                            Handle<Object> exception) {
    v8::Local<v8::Promise::Resolver> resolver;
    ASSIGN_RETURN_ON_SCHEDULED_EXCEPTION_VALUE(
        isolate, resolver, v8::Promise::Resolver::New(api_context),
        MaybeHandle<JSPromise>());
  
    RETURN_ON_SCHEDULED_EXCEPTION_VALUE(
        isolate, resolver->Reject(api_context, v8::Utils::ToLocal(exception)),
        MaybeHandle<JSPromise>());
  
    v8::Local<v8::Promise> promise = resolver->GetPromise();
    return v8::Utils::OpenHandle(*promise);
  }
  
  }  // namespace
  
  MaybeHandle<JSPromise> Isolate::RunHostImportModuleDynamicallyCallback(
      Handle<Script> referrer, Handle<Object> specifier,
      MaybeHandle<Object> maybe_import_assertions_argument) {
    v8::Local<v8::Context> api_context =
        v8::Utils::ToLocal(Handle<Context>(native_context()));
    DCHECK(host_import_module_dynamically_callback_ == nullptr ||
           host_import_module_dynamically_with_import_assertions_callback_ ==
               nullptr);
  
    if (host_import_module_dynamically_callback_ == nullptr &&
        host_import_module_dynamically_with_import_assertions_callback_ ==
            nullptr) {
      Handle<Object> exception =
          factory()->NewError(error_function(), MessageTemplate::kUnsupported);
      return NewRejectedPromise(this, api_context, exception);
    }
  
    Handle<String> specifier_str;
    MaybeHandle<String> maybe_specifier = Object::ToString(this, specifier);
    if (!maybe_specifier.ToHandle(&specifier_str)) {
      Handle<Object> exception(pending_exception(), this);
      clear_pending_exception();
  
      return NewRejectedPromise(this, api_context, exception);
    }
    DCHECK(!has_pending_exception());
  
    v8::Local<v8::Promise> promise;
  
    if (host_import_module_dynamically_with_import_assertions_callback_) {
      Handle<FixedArray> import_assertions_array;
      if (GetImportAssertionsFromArgument(maybe_import_assertions_argument)
              .ToHandle(&import_assertions_array)) {
        ASSIGN_RETURN_ON_SCHEDULED_EXCEPTION_VALUE(
            this, promise,
            host_import_module_dynamically_with_import_assertions_callback_(
                api_context, v8::Utils::ScriptOrModuleToLocal(referrer),
                v8::Utils::ToLocal(specifier_str),
                ToApiHandle<v8::FixedArray>(import_assertions_array)),
            MaybeHandle<JSPromise>());
        return v8::Utils::OpenHandle(*promise);
      } else {
        Handle<Object> exception(pending_exception(), this);
        clear_pending_exception();
  
        return NewRejectedPromise(this, api_context, exception);
      }
  
    } else {
      DCHECK_NOT_NULL(host_import_module_dynamically_callback_);
      ASSIGN_RETURN_ON_SCHEDULED_EXCEPTION_VALUE(
          this, promise,
          host_import_module_dynamically_callback_(
              api_context, v8::Utils::ScriptOrModuleToLocal(referrer),
              v8::Utils::ToLocal(specifier_str)),
          MaybeHandle<JSPromise>());
      return v8::Utils::OpenHandle(*promise);
    }
  }
  
  MaybeHandle<FixedArray> Isolate::GetImportAssertionsFromArgument(
      MaybeHandle<Object> maybe_import_assertions_argument) {
    Handle<FixedArray> import_assertions_array = factory()->empty_fixed_array();
    Handle<Object> import_assertions_argument;
    if (!maybe_import_assertions_argument.ToHandle(&import_assertions_argument) ||
        import_assertions_argument->IsUndefined()) {
      return import_assertions_array;
    }
  
    // The parser shouldn't have allowed the second argument to import() if
    // the flag wasn't enabled.
    DCHECK(FLAG_harmony_import_assertions);
  
    if (!import_assertions_argument->IsJSReceiver()) {
      this->Throw(
          *factory()->NewTypeError(MessageTemplate::kNonObjectImportArgument));
      return MaybeHandle<FixedArray>();
    }
  
    Handle<JSReceiver> import_assertions_argument_receiver =
        Handle<JSReceiver>::cast(import_assertions_argument);
    Handle<Name> key = factory()->assert_string();
  
    Handle<Object> import_assertions_object;
    if (!JSReceiver::GetProperty(this, import_assertions_argument_receiver, key)
             .ToHandle(&import_assertions_object)) {
      // This can happen if the property has a getter function that throws
      // an error.
      return MaybeHandle<FixedArray>();
    }
  
    // If there is no 'assert' option in the options bag, it's not an error. Just
    // do the import() as if no assertions were provided.
    if (import_assertions_object->IsUndefined()) return import_assertions_array;
  
    if (!import_assertions_object->IsJSReceiver()) {
      this->Throw(
          *factory()->NewTypeError(MessageTemplate::kNonObjectAssertOption));
      return MaybeHandle<FixedArray>();
    }
  
    Handle<JSReceiver> import_assertions_object_receiver =
        Handle<JSReceiver>::cast(import_assertions_object);
  
    Handle<FixedArray> assertion_keys =
        KeyAccumulator::GetKeys(import_assertions_object_receiver,
                                KeyCollectionMode::kOwnOnly, ENUMERABLE_STRINGS,
                                GetKeysConversion::kConvertToString)
            .ToHandleChecked();
  
    // The assertions will be passed to the host in the form: [key1,
    // value1, key2, value2, ...].
    constexpr size_t kAssertionEntrySizeForDynamicImport = 2;
    import_assertions_array = factory()->NewFixedArray(static_cast<int>(
        assertion_keys->length() * kAssertionEntrySizeForDynamicImport));
    for (int i = 0; i < assertion_keys->length(); i++) {
      Handle<String> assertion_key(String::cast(assertion_keys->get(i)), this);
      Handle<Object> assertion_value;
      if (!JSReceiver::GetProperty(this, import_assertions_object_receiver,
                                   assertion_key)
               .ToHandle(&assertion_value)) {
        // This can happen if the property has a getter function that throws
        // an error.
        return MaybeHandle<FixedArray>();
      }
  
      if (!assertion_value->IsString()) {
        this->Throw(*factory()->NewTypeError(
            MessageTemplate::kNonStringImportAssertionValue));
        return MaybeHandle<FixedArray>();
      }
  
      import_assertions_array->set((i * kAssertionEntrySizeForDynamicImport),
                                   *assertion_key);
      import_assertions_array->set((i * kAssertionEntrySizeForDynamicImport) + 1,
                                   *assertion_value);
    }
  
    return import_assertions_array;
  }
  
  void Isolate::ClearKeptObjects() { heap()->ClearKeptObjects(); }
  
  void Isolate::SetHostImportModuleDynamicallyCallback(
      DeprecatedHostImportModuleDynamicallyCallback callback) {
    host_import_module_dynamically_callback_ = callback;
  }
  
  void Isolate::SetHostImportModuleDynamicallyCallback(
      HostImportModuleDynamicallyWithImportAssertionsCallback callback) {
    host_import_module_dynamically_with_import_assertions_callback_ = callback;
  }
  
  MaybeHandle<JSObject> Isolate::RunHostInitializeImportMetaObjectCallback(
      Handle<SourceTextModule> module) {
    CHECK(module->import_meta().IsTheHole(this));
    Handle<JSObject> import_meta = factory()->NewJSObjectWithNullProto();
    if (host_initialize_import_meta_object_callback_ != nullptr) {
      v8::Local<v8::Context> api_context =
          v8::Utils::ToLocal(Handle<Context>(native_context()));
      host_initialize_import_meta_object_callback_(
          api_context, Utils::ToLocal(Handle<Module>::cast(module)),
          v8::Local<v8::Object>::Cast(v8::Utils::ToLocal(import_meta)));
      if (has_scheduled_exception()) {
        PromoteScheduledException();
        return {};
      }
    }
    return import_meta;
  }
  
  void Isolate::SetHostInitializeImportMetaObjectCallback(
      HostInitializeImportMetaObjectCallback callback) {
    host_initialize_import_meta_object_callback_ = callback;
  }
  
  MaybeHandle<Object> Isolate::RunPrepareStackTraceCallback(
      Handle<Context> context, Handle<JSObject> error, Handle<JSArray> sites) {
    v8::Local<v8::Context> api_context = Utils::ToLocal(context);
  
    v8::Local<v8::Value> stack;
    ASSIGN_RETURN_ON_SCHEDULED_EXCEPTION_VALUE(
        this, stack,
        prepare_stack_trace_callback_(api_context, Utils::ToLocal(error),
                                      Utils::ToLocal(sites)),
        MaybeHandle<Object>());
    return Utils::OpenHandle(*stack);
  }
  
  int Isolate::LookupOrAddExternallyCompiledFilename(const char* filename) {
    if (embedded_file_writer_ != nullptr) {
      return embedded_file_writer_->LookupOrAddExternallyCompiledFilename(
          filename);
    }
    return 0;
  }
  
  const char* Isolate::GetExternallyCompiledFilename(int index) const {
    if (embedded_file_writer_ != nullptr) {
      return embedded_file_writer_->GetExternallyCompiledFilename(index);
    }
    return "";
  }
  
  int Isolate::GetExternallyCompiledFilenameCount() const {
    if (embedded_file_writer_ != nullptr) {
      return embedded_file_writer_->GetExternallyCompiledFilenameCount();
    }
    return 0;
  }
  
  void Isolate::PrepareBuiltinSourcePositionMap() {
    if (embedded_file_writer_ != nullptr) {
      return embedded_file_writer_->PrepareBuiltinSourcePositionMap(
          this->builtins());
    }
  }
  
  void Isolate::PrepareBuiltinLabelInfoMap() {
    if (embedded_file_writer_ != nullptr) {
      embedded_file_writer_->PrepareBuiltinLabelInfoMap(
          heap()->construct_stub_create_deopt_pc_offset().value(),
          heap()->construct_stub_invoke_deopt_pc_offset().value());
    }
  }
  
  #if defined(V8_OS_WIN64)
  void Isolate::SetBuiltinUnwindData(
      int builtin_index,
      const win64_unwindinfo::BuiltinUnwindInfo& unwinding_info) {
    if (embedded_file_writer_ != nullptr) {
      embedded_file_writer_->SetBuiltinUnwindData(builtin_index, unwinding_info);
    }
  }
  #endif  // V8_OS_WIN64
  
  void Isolate::SetPrepareStackTraceCallback(PrepareStackTraceCallback callback) {
    prepare_stack_trace_callback_ = callback;
  }
  
  bool Isolate::HasPrepareStackTraceCallback() const {
    return prepare_stack_trace_callback_ != nullptr;
  }
  
  void Isolate::SetAddCrashKeyCallback(AddCrashKeyCallback callback) {
    add_crash_key_callback_ = callback;
  
    // Log the initial set of data.
    AddCrashKeysForIsolateAndHeapPointers();
  }
  
  void Isolate::SetAtomicsWaitCallback(v8::Isolate::AtomicsWaitCallback callback,
                                       void* data) {
    atomics_wait_callback_ = callback;
    atomics_wait_callback_data_ = data;
  }
  
  void Isolate::RunAtomicsWaitCallback(v8::Isolate::AtomicsWaitEvent event,
                                       Handle<JSArrayBuffer> array_buffer,
                                       size_t offset_in_bytes, int64_t value,
                                       double timeout_in_ms,
                                       AtomicsWaitWakeHandle* stop_handle) {
    DCHECK(array_buffer->is_shared());
    if (atomics_wait_callback_ == nullptr) return;
    HandleScope handle_scope(this);
    atomics_wait_callback_(
        event, v8::Utils::ToLocalShared(array_buffer), offset_in_bytes, value,
        timeout_in_ms,
        reinterpret_cast<v8::Isolate::AtomicsWaitWakeHandle*>(stop_handle),
        atomics_wait_callback_data_);
  }
  
  void Isolate::SetPromiseHook(PromiseHook hook) {
    promise_hook_ = hook;
    PromiseHookStateUpdated();
  }
  
  void Isolate::RunAllPromiseHooks(PromiseHookType type,
                                   Handle<JSPromise> promise,
                                   Handle<Object> parent) {
    if (HasContextPromiseHooks()) {
      native_context()->RunPromiseHook(type, promise, parent);
    }
    if (HasIsolatePromiseHooks() || HasAsyncEventDelegate()) {
      RunPromiseHook(type, promise, parent);
    }
  }
  
  void Isolate::RunPromiseHook(PromiseHookType type, Handle<JSPromise> promise,
                               Handle<Object> parent) {
    RunPromiseHookForAsyncEventDelegate(type, promise);
    if (!HasIsolatePromiseHooks()) return;
    DCHECK(promise_hook_ != nullptr);
    promise_hook_(type, v8::Utils::PromiseToLocal(promise),
                  v8::Utils::ToLocal(parent));
  }
  
  void Isolate::RunPromiseHookForAsyncEventDelegate(PromiseHookType type,
                                                    Handle<JSPromise> promise) {
    if (!HasAsyncEventDelegate()) return;
    DCHECK(async_event_delegate_ != nullptr);
    switch (type) {
      case PromiseHookType::kResolve:
        return;
      case PromiseHookType::kBefore:
        if (!promise->async_task_id()) return;
        async_event_delegate_->AsyncEventOccurred(
            debug::kDebugWillHandle, promise->async_task_id(), false);
        break;
      case PromiseHookType::kAfter:
        if (!promise->async_task_id()) return;
        async_event_delegate_->AsyncEventOccurred(
            debug::kDebugDidHandle, promise->async_task_id(), false);
        break;
      case PromiseHookType::kInit:
        debug::DebugAsyncActionType type = debug::kDebugPromiseThen;
        bool last_frame_was_promise_builtin = false;
        JavaScriptFrameIterator it(this);
        while (!it.done()) {
          std::vector<Handle<SharedFunctionInfo>> infos;
          it.frame()->GetFunctions(&infos);
          for (size_t i = 1; i <= infos.size(); ++i) {
            Handle<SharedFunctionInfo> info = infos[infos.size() - i];
            if (info->IsUserJavaScript()) {
              // We should not report PromiseThen and PromiseCatch which is called
              // indirectly, e.g. Promise.all calls Promise.then internally.
              if (last_frame_was_promise_builtin) {
                if (!promise->async_task_id()) {
                  promise->set_async_task_id(++async_task_count_);
                }
                async_event_delegate_->AsyncEventOccurred(
                    type, promise->async_task_id(), debug()->IsBlackboxed(info));
              }
              return;
            }
            last_frame_was_promise_builtin = false;
            if (info->HasBuiltinId()) {
              if (info->builtin_id() == Builtins::kPromisePrototypeThen) {
                type = debug::kDebugPromiseThen;
                last_frame_was_promise_builtin = true;
              } else if (info->builtin_id() == Builtins::kPromisePrototypeCatch) {
                type = debug::kDebugPromiseCatch;
                last_frame_was_promise_builtin = true;
              } else if (info->builtin_id() ==
                         Builtins::kPromisePrototypeFinally) {
                type = debug::kDebugPromiseFinally;
                last_frame_was_promise_builtin = true;
              }
            }
          }
          it.Advance();
        }
    }
  }
  
  void Isolate::OnAsyncFunctionStateChanged(Handle<JSPromise> promise,
                                            debug::DebugAsyncActionType event) {
    if (!async_event_delegate_) return;
    if (!promise->async_task_id()) {
      promise->set_async_task_id(++async_task_count_);
    }
    async_event_delegate_->AsyncEventOccurred(event, promise->async_task_id(),
                                              false);
  }
  
  void Isolate::SetPromiseRejectCallback(PromiseRejectCallback callback) {
    promise_reject_callback_ = callback;
  }
  
  void Isolate::ReportPromiseReject(Handle<JSPromise> promise,
                                    Handle<Object> value,
                                    v8::PromiseRejectEvent event) {
    if (promise_reject_callback_ == nullptr) return;
    promise_reject_callback_(v8::PromiseRejectMessage(
        v8::Utils::PromiseToLocal(promise), event, v8::Utils::ToLocal(value)));
  }
  
  void Isolate::SetUseCounterCallback(v8::Isolate::UseCounterCallback callback) {
    DCHECK(!use_counter_callback_);
    use_counter_callback_ = callback;
  }
  
  void Isolate::CountUsage(v8::Isolate::UseCounterFeature feature) {
    // The counter callback
    // - may cause the embedder to call into V8, which is not generally possible
    //   during GC.
    // - requires a current native context, which may not always exist.
    // TODO(jgruber): Consider either removing the native context requirement in
    // blink, or passing it to the callback explicitly.
    if (heap_.gc_state() == Heap::NOT_IN_GC && !context().is_null()) {
      DCHECK(context().IsContext());
      DCHECK(context().native_context().IsNativeContext());
      if (use_counter_callback_) {
        HandleScope handle_scope(this);
        use_counter_callback_(reinterpret_cast<v8::Isolate*>(this), feature);
      }
    } else {
      heap_.IncrementDeferredCount(feature);
    }
  }
  
  int Isolate::GetNextScriptId() { return heap()->NextScriptId(); }
  
  // static
  std::string Isolate::GetTurboCfgFileName(Isolate* isolate) {
    if (FLAG_trace_turbo_cfg_file == nullptr) {
      std::ostringstream os;
      os << "turbo-" << base::OS::GetCurrentProcessId() << "-";
      if (isolate != nullptr) {
        os << isolate->id();
      } else {
        os << "any";
      }
      os << ".cfg";
      return os.str();
    } else {
      return FLAG_trace_turbo_cfg_file;
    }
  }
  
  // Heap::detached_contexts tracks detached contexts as pairs
  // (number of GC since the context was detached, the context).
  void Isolate::AddDetachedContext(Handle<Context> context) {
    HandleScope scope(this);
    Handle<WeakArrayList> detached_contexts = factory()->detached_contexts();
    detached_contexts = WeakArrayList::AddToEnd(
        this, detached_contexts, MaybeObjectHandle(Smi::zero(), this),
        MaybeObjectHandle::Weak(context));
    heap()->set_detached_contexts(*detached_contexts);
  }
  
  void Isolate::CheckDetachedContextsAfterGC() {
    HandleScope scope(this);
    Handle<WeakArrayList> detached_contexts = factory()->detached_contexts();
    int length = detached_contexts->length();
    if (length == 0) return;
    int new_length = 0;
    for (int i = 0; i < length; i += 2) {
      int mark_sweeps = detached_contexts->Get(i).ToSmi().value();
      MaybeObject context = detached_contexts->Get(i + 1);
      DCHECK(context->IsWeakOrCleared());
      if (!context->IsCleared()) {
        detached_contexts->Set(
            new_length, MaybeObject::FromSmi(Smi::FromInt(mark_sweeps + 1)));
        detached_contexts->Set(new_length + 1, context);
        new_length += 2;
      }
    }
    detached_contexts->set_length(new_length);
    while (new_length < length) {
      detached_contexts->Set(new_length, MaybeObject::FromSmi(Smi::zero()));
      ++new_length;
    }
  
    if (FLAG_trace_detached_contexts) {
      PrintF("%d detached contexts are collected out of %d\n",
             length - new_length, length);
      for (int i = 0; i < new_length; i += 2) {
        int mark_sweeps = detached_contexts->Get(i).ToSmi().value();
        MaybeObject context = detached_contexts->Get(i + 1);
        DCHECK(context->IsWeakOrCleared());
        if (mark_sweeps > 3) {
          PrintF("detached context %p\n survived %d GCs (leak?)\n",
                 reinterpret_cast<void*>(context.ptr()), mark_sweeps);
        }
      }
    }
  }
  
  double Isolate::LoadStartTimeMs() {
    base::MutexGuard guard(&rail_mutex_);
    return load_start_time_ms_;
  }
  
  void Isolate::UpdateLoadStartTime() {
    base::MutexGuard guard(&rail_mutex_);
    load_start_time_ms_ = heap()->MonotonicallyIncreasingTimeInMs();
  }
  
  void Isolate::SetRAILMode(RAILMode rail_mode) {
    RAILMode old_rail_mode = rail_mode_.load();
    if (old_rail_mode != PERFORMANCE_LOAD && rail_mode == PERFORMANCE_LOAD) {
      base::MutexGuard guard(&rail_mutex_);
      load_start_time_ms_ = heap()->MonotonicallyIncreasingTimeInMs();
    }
    rail_mode_.store(rail_mode);
    if (old_rail_mode == PERFORMANCE_LOAD && rail_mode != PERFORMANCE_LOAD) {
      heap()->incremental_marking()->incremental_marking_job()->ScheduleTask(
          heap());
    }
    if (FLAG_trace_rail) {
      PrintIsolate(this, "RAIL mode: %s\n", RAILModeName(rail_mode));
    }
  }
  
  void Isolate::IsolateInBackgroundNotification() {
    is_isolate_in_background_ = true;
    heap()->ActivateMemoryReducerIfNeeded();
  }
  
  void Isolate::IsolateInForegroundNotification() {
    is_isolate_in_background_ = false;
  }
  
  void Isolate::PrintWithTimestamp(const char* format, ...) {
    base::OS::Print("[%d:%p] %8.0f ms: ", base::OS::GetCurrentProcessId(),
                    static_cast<void*>(this), time_millis_since_init());
    va_list arguments;
    va_start(arguments, format);
    base::OS::VPrint(format, arguments);
    va_end(arguments);
  }
  
  void Isolate::SetIdle(bool is_idle) {
    StateTag state = current_vm_state();
    if (js_entry_sp() != kNullAddress) return;
    DCHECK(state == EXTERNAL || state == IDLE);
    if (is_idle) {
      set_current_vm_state(IDLE);
    } else if (state == IDLE) {
      set_current_vm_state(EXTERNAL);
    }
  }
  
  void Isolate::CollectSourcePositionsForAllBytecodeArrays() {
    HandleScope scope(this);
    std::vector<Handle<SharedFunctionInfo>> sfis;
    {
      DisallowGarbageCollection no_gc;
      HeapObjectIterator iterator(heap());
      for (HeapObject obj = iterator.Next(); !obj.is_null();
           obj = iterator.Next()) {
        if (obj.IsSharedFunctionInfo()) {
          SharedFunctionInfo sfi = SharedFunctionInfo::cast(obj);
          if (sfi.HasBytecodeArray()) {
            sfis.push_back(Handle<SharedFunctionInfo>(sfi, this));
          }
        }
      }
    }
    for (auto sfi : sfis) {
      SharedFunctionInfo::EnsureSourcePositionsAvailable(this, sfi);
    }
  }
  
  #ifdef V8_INTL_SUPPORT
  namespace {
  std::string GetStringFromLocale(Handle<Object> locales_obj) {
    DCHECK(locales_obj->IsString() || locales_obj->IsUndefined());
    if (locales_obj->IsString()) {
      return std::string(String::cast(*locales_obj).ToCString().get());
    }
  
    return "";
  }
  }  // namespace
  
  icu::UMemory* Isolate::get_cached_icu_object(ICUObjectCacheType cache_type,
                                               Handle<Object> locales_obj) {
    std::string locale = GetStringFromLocale(locales_obj);
    auto value = icu_object_cache_.find(cache_type);
    if (value == icu_object_cache_.end()) return nullptr;
  
    ICUCachePair pair = value->second;
    if (pair.first != locale) return nullptr;
  
    return pair.second.get();
  }
  
  void Isolate::set_icu_object_in_cache(
      ICUObjectCacheType cache_type, Handle<Object> locales_obj,
      std::shared_ptr<icu::UMemory> icu_formatter) {
    std::string locale = GetStringFromLocale(locales_obj);
    ICUCachePair pair = std::make_pair(locale, icu_formatter);
  
    auto it = icu_object_cache_.find(cache_type);
    if (it == icu_object_cache_.end()) {
      icu_object_cache_.insert({cache_type, pair});
    } else {
      it->second = pair;
    }
  }
  
  void Isolate::clear_cached_icu_object(ICUObjectCacheType cache_type) {
    icu_object_cache_.erase(cache_type);
  }
  
  void Isolate::ClearCachedIcuObjects() { icu_object_cache_.clear(); }
  
  #endif  // V8_INTL_SUPPORT
  
  bool StackLimitCheck::JsHasOverflowed(uintptr_t gap) const {
    StackGuard* stack_guard = isolate_->stack_guard();
  #ifdef USE_SIMULATOR
    // The simulator uses a separate JS stack.
    Address jssp_address = Simulator::current(isolate_)->get_sp();
    uintptr_t jssp = static_cast<uintptr_t>(jssp_address);
    if (jssp - gap < stack_guard->real_jslimit()) return true;
  #endif  // USE_SIMULATOR
    return GetCurrentStackPosition() - gap < stack_guard->real_climit();
  }
  
  SaveContext::SaveContext(Isolate* isolate) : isolate_(isolate) {
    if (!isolate->context().is_null()) {
      context_ = Handle<Context>(isolate->context(), isolate);
    }
  
    c_entry_fp_ = isolate->c_entry_fp(isolate->thread_local_top());
  }
  
  SaveContext::~SaveContext() {
    isolate_->set_context(context_.is_null() ? Context() : *context_);
  }
  
  bool SaveContext::IsBelowFrame(CommonFrame* frame) {
    return (c_entry_fp_ == 0) || (c_entry_fp_ > frame->sp());
  }
  
  SaveAndSwitchContext::SaveAndSwitchContext(Isolate* isolate,
                                             Context new_context)
      : SaveContext(isolate) {
    isolate->set_context(new_context);
  }
  
  #ifdef DEBUG
  AssertNoContextChange::AssertNoContextChange(Isolate* isolate)
      : isolate_(isolate), context_(isolate->context(), isolate) {}
  
  namespace {
  
  bool Overlapping(const MemoryRange& a, const MemoryRange& b) {
    uintptr_t a1 = reinterpret_cast<uintptr_t>(a.start);
    uintptr_t a2 = a1 + a.length_in_bytes;
    uintptr_t b1 = reinterpret_cast<uintptr_t>(b.start);
    uintptr_t b2 = b1 + b.length_in_bytes;
    // Either b1 or b2 are in the [a1, a2) range.
    return (a1 <= b1 && b1 < a2) || (a1 <= b2 && b2 < a2);
  }
  
  }  // anonymous namespace
  
  #endif  // DEBUG
  
  void Isolate::AddCodeMemoryRange(MemoryRange range) {
    std::vector<MemoryRange>* old_code_pages = GetCodePages();
    DCHECK_NOT_NULL(old_code_pages);
  #ifdef DEBUG
    auto overlapping = [range](const MemoryRange& a) {
      return Overlapping(range, a);
    };
    DCHECK_EQ(old_code_pages->end(),
              std::find_if(old_code_pages->begin(), old_code_pages->end(),
                           overlapping));
  #endif
  
    std::vector<MemoryRange>* new_code_pages;
    if (old_code_pages == &code_pages_buffer1_) {
      new_code_pages = &code_pages_buffer2_;
    } else {
      new_code_pages = &code_pages_buffer1_;
    }
  
    // Copy all existing data from the old vector to the new vector and insert the
    // new page.
    new_code_pages->clear();
    new_code_pages->reserve(old_code_pages->size() + 1);
    std::merge(old_code_pages->begin(), old_code_pages->end(), &range, &range + 1,
               std::back_inserter(*new_code_pages),
               [](const MemoryRange& a, const MemoryRange& b) {
                 return a.start < b.start;
               });
  
    // Atomically switch out the pointer
    SetCodePages(new_code_pages);
  }
  
  // |chunk| is either a Page or an executable LargePage.
  void Isolate::AddCodeMemoryChunk(MemoryChunk* chunk) {
    // We only keep track of individual code pages/allocations if we are on arm32,
    // because on x64 and arm64 we have a code range which makes this unnecessary.
  #if !defined(V8_TARGET_ARCH_ARM)
    return;
  #else
    void* new_page_start = reinterpret_cast<void*>(chunk->area_start());
    size_t new_page_size = chunk->area_size();
  
    MemoryRange new_range{new_page_start, new_page_size};
  
    AddCodeMemoryRange(new_range);
  #endif  // !defined(V8_TARGET_ARCH_ARM)
  }
  
  void Isolate::AddCodeRange(Address begin, size_t length_in_bytes) {
    AddCodeMemoryRange(
        MemoryRange{reinterpret_cast<void*>(begin), length_in_bytes});
  }
  
  bool Isolate::RequiresCodeRange() const {
    return kPlatformRequiresCodeRange && !jitless_;
  }
  
  v8::metrics::Recorder::ContextId Isolate::GetOrRegisterRecorderContextId(
      Handle<NativeContext> context) {
    if (serializer_enabled_) return v8::metrics::Recorder::ContextId::Empty();
    i::Object id = context->recorder_context_id();
    if (id.IsNullOrUndefined()) {
      CHECK_LT(last_recorder_context_id_, i::Smi::kMaxValue);
      context->set_recorder_context_id(
          i::Smi::FromIntptr(++last_recorder_context_id_));
      v8::HandleScope handle_scope(reinterpret_cast<v8::Isolate*>(this));
      auto result = recorder_context_id_map_.emplace(
          std::piecewise_construct,
          std::forward_as_tuple(last_recorder_context_id_),
          std::forward_as_tuple(reinterpret_cast<v8::Isolate*>(this),
                                ToApiHandle<v8::Context>(context)));
      result.first->second.SetWeak(
          reinterpret_cast<void*>(last_recorder_context_id_),
          RemoveContextIdCallback, v8::WeakCallbackType::kParameter);
      return v8::metrics::Recorder::ContextId(last_recorder_context_id_);
    } else {
      DCHECK(id.IsSmi());
      return v8::metrics::Recorder::ContextId(
          static_cast<uintptr_t>(i::Smi::ToInt(id)));
    }
  }
  
  MaybeLocal<v8::Context> Isolate::GetContextFromRecorderContextId(
      v8::metrics::Recorder::ContextId id) {
    auto result = recorder_context_id_map_.find(id.id_);
    if (result == recorder_context_id_map_.end() || result->second.IsEmpty())
      return MaybeLocal<v8::Context>();
    return result->second.Get(reinterpret_cast<v8::Isolate*>(this));
  }
  
  void Isolate::UpdateLongTaskStats() {
    if (last_long_task_stats_counter_ != isolate_data_.long_task_stats_counter_) {
      last_long_task_stats_counter_ = isolate_data_.long_task_stats_counter_;
      long_task_stats_ = v8::metrics::LongTaskStats{};
    }
  }
  
  v8::metrics::LongTaskStats* Isolate::GetCurrentLongTaskStats() {
    UpdateLongTaskStats();
    return &long_task_stats_;
  }
  
  void Isolate::RemoveContextIdCallback(const v8::WeakCallbackInfo<void>& data) {
    Isolate* isolate = reinterpret_cast<Isolate*>(data.GetIsolate());
    uintptr_t context_id = reinterpret_cast<uintptr_t>(data.GetParameter());
    isolate->recorder_context_id_map_.erase(context_id);
  }
  
  LocalHeap* Isolate::main_thread_local_heap() {
    return main_thread_local_isolate()->heap();
  }
  
  LocalHeap* Isolate::CurrentLocalHeap() {
    LocalHeap* local_heap = LocalHeap::Current();
    return local_heap ? local_heap : main_thread_local_heap();
  }
  
  // |chunk| is either a Page or an executable LargePage.
  void Isolate::RemoveCodeMemoryChunk(MemoryChunk* chunk) {
    // We only keep track of individual code pages/allocations if we are on arm32,
    // because on x64 and arm64 we have a code range which makes this unnecessary.
  #if !defined(V8_TARGET_ARCH_ARM)
    return;
  #else
    void* removed_page_start = reinterpret_cast<void*>(chunk->area_start());
    std::vector<MemoryRange>* old_code_pages = GetCodePages();
    DCHECK_NOT_NULL(old_code_pages);
  
    std::vector<MemoryRange>* new_code_pages;
    if (old_code_pages == &code_pages_buffer1_) {
      new_code_pages = &code_pages_buffer2_;
    } else {
      new_code_pages = &code_pages_buffer1_;
    }
  
    // Copy all existing data from the old vector to the new vector except the
    // removed page.
    new_code_pages->clear();
    new_code_pages->reserve(old_code_pages->size() - 1);
    std::remove_copy_if(old_code_pages->begin(), old_code_pages->end(),
                        std::back_inserter(*new_code_pages),
                        [removed_page_start](const MemoryRange& range) {
                          return range.start == removed_page_start;
                        });
    DCHECK_EQ(old_code_pages->size(), new_code_pages->size() + 1);
    // Atomically switch out the pointer
    SetCodePages(new_code_pages);
  #endif  // !defined(V8_TARGET_ARCH_ARM)
  }
  
  #undef TRACE_ISOLATE
  
  // static
  Address Isolate::load_from_stack_count_address(const char* function_name) {
    DCHECK_NOT_NULL(function_name);
    if (!stack_access_count_map) {
      stack_access_count_map = new MapOfLoadsAndStoresPerFunction{};
    }
    auto& map = *stack_access_count_map;
    std::string name(function_name);
    // It is safe to return the address of std::map values.
    // Only iterators and references to the erased elements are invalidated.
    return reinterpret_cast<Address>(&map[name].first);
  }
  
  // static
  Address Isolate::store_to_stack_count_address(const char* function_name) {
    DCHECK_NOT_NULL(function_name);
    if (!stack_access_count_map) {
      stack_access_count_map = new MapOfLoadsAndStoresPerFunction{};
    }
    auto& map = *stack_access_count_map;
    std::string name(function_name);
    // It is safe to return the address of std::map values.
    // Only iterators and references to the erased elements are invalidated.
    return reinterpret_cast<Address>(&map[name].second);
  }
  
  void Isolate::AttachToSharedIsolate(Isolate* shared) {
    DCHECK(shared->is_shared());
    DCHECK_NULL(shared_isolate_);
    shared->AppendAsClientIsolate(this);
    shared_isolate_ = shared;
    heap()->InitSharedSpaces();
  }
  
  void Isolate::DetachFromSharedIsolate() {
    DCHECK_NOT_NULL(shared_isolate_);
    shared_isolate_->RemoveAsClientIsolate(this);
    shared_isolate_ = nullptr;
    heap()->DeinitSharedSpaces();
  }
  
  void Isolate::AppendAsClientIsolate(Isolate* client) {
    base::MutexGuard guard(&client_isolate_mutex_);
  
    DCHECK_NULL(client->prev_client_isolate_);
    DCHECK_NULL(client->next_client_isolate_);
    DCHECK_NE(client_isolate_head_, client);
  
    if (client_isolate_head_) {
      client_isolate_head_->prev_client_isolate_ = client;
    }
  
    client->prev_client_isolate_ = nullptr;
    client->next_client_isolate_ = client_isolate_head_;
  
    client_isolate_head_ = client;
  }
  
  void Isolate::RemoveAsClientIsolate(Isolate* client) {
    base::MutexGuard guard(&client_isolate_mutex_);
  
    if (client->next_client_isolate_) {
      client->next_client_isolate_->prev_client_isolate_ =
          client->prev_client_isolate_;
    }
  
    if (client->prev_client_isolate_) {
      client->prev_client_isolate_->next_client_isolate_ =
          client->next_client_isolate_;
    } else {
      DCHECK_EQ(client_isolate_head_, client);
      client_isolate_head_ = client->next_client_isolate_;
    }
  }
  
  }  // namespace internal
  }  // namespace v8
  