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/isolate.h"
  
  #include <stdlib.h>
  
  #include <atomic>
  #include <fstream>  // NOLINT(readability/streams)
  #include <memory>
  #include <sstream>
  #include <unordered_map>
  
  #include "src/api-inl.h"
  #include "src/assembler-inl.h"
  #include "src/ast/ast-value-factory.h"
  #include "src/ast/scopes.h"
  #include "src/base/adapters.h"
  #include "src/base/hashmap.h"
  #include "src/base/platform/platform.h"
  #include "src/base/sys-info.h"
  #include "src/base/utils/random-number-generator.h"
  #include "src/bootstrapper.h"
  #include "src/builtins/builtins-promise.h"
  #include "src/builtins/constants-table-builder.h"
  #include "src/cancelable-task.h"
  #include "src/compilation-cache.h"
  #include "src/compilation-statistics.h"
  #include "src/compiler-dispatcher/compiler-dispatcher.h"
  #include "src/compiler-dispatcher/optimizing-compile-dispatcher.h"
  #include "src/date.h"
  #include "src/debug/debug-frames.h"
  #include "src/debug/debug.h"
  #include "src/deoptimizer.h"
  #include "src/elements.h"
  #include "src/frames-inl.h"
  #include "src/ic/stub-cache.h"
  #include "src/interpreter/interpreter.h"
  #include "src/isolate-inl.h"
  #include "src/libsampler/sampler.h"
  #include "src/log.h"
  #include "src/messages.h"
  #include "src/microtask-queue.h"
  #include "src/objects/frame-array-inl.h"
  #include "src/objects/hash-table-inl.h"
  #include "src/objects/js-array-inl.h"
  #include "src/objects/js-generator-inl.h"
  #include "src/objects/module-inl.h"
  #include "src/objects/promise-inl.h"
  #include "src/objects/slots.h"
  #include "src/objects/smi.h"
  #include "src/objects/stack-frame-info-inl.h"
  #include "src/profiler/tracing-cpu-profiler.h"
  #include "src/prototype.h"
  #include "src/ptr-compr.h"
  #include "src/regexp/regexp-stack.h"
  #include "src/runtime-profiler.h"
  #include "src/setup-isolate.h"
  #include "src/simulator.h"
  #include "src/snapshot/embedded-data.h"
  #include "src/snapshot/startup-deserializer.h"
  #include "src/tracing/tracing-category-observer.h"
  #include "src/trap-handler/trap-handler.h"
  #include "src/unicode-cache.h"
  #include "src/v8.h"
  #include "src/version.h"
  #include "src/visitors.h"
  #include "src/vm-state-inl.h"
  #include "src/wasm/wasm-code-manager.h"
  #include "src/wasm/wasm-engine.h"
  #include "src/wasm/wasm-objects.h"
  #include "src/zone/accounting-allocator.h"
  #ifdef V8_INTL_SUPPORT
  #include "unicode/uobject.h"
  #endif  // V8_INTL_SUPPORT
  
  extern "C" const uint8_t* v8_Default_embedded_blob_;
  extern "C" uint32_t v8_Default_embedded_blob_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* DefaultEmbeddedBlob() { return v8_Default_embedded_blob_; }
  uint32_t DefaultEmbeddedBlobSize() { return v8_Default_embedded_blob_size_; }
  
  #ifdef V8_MULTI_SNAPSHOTS
  extern "C" const uint8_t* v8_Trusted_embedded_blob_;
  extern "C" uint32_t v8_Trusted_embedded_blob_size_;
  
  const uint8_t* TrustedEmbeddedBlob() { return v8_Trusted_embedded_blob_; }
  uint32_t TrustedEmbeddedBlobSize() { return v8_Trusted_embedded_blob_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_(nullptr);
  std::atomic<uint32_t> current_embedded_blob_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_
  // - sticky_embedded_blob_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_ = nullptr;
  uint32_t sticky_embedded_blob_size_ = 0;
  
  bool enable_embedded_blob_refcounting_ = true;
  int current_embedded_blob_refs_ = 0;
  
  const uint8_t* StickyEmbeddedBlob() { return sticky_embedded_blob_; }
  uint32_t StickyEmbeddedBlobSize() { return sticky_embedded_blob_size_; }
  
  void SetStickyEmbeddedBlob(const uint8_t* blob, uint32_t blob_size) {
    sticky_embedded_blob_ = blob;
    sticky_embedded_blob_size_ = blob_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 (StickyEmbeddedBlob() == nullptr) return;
  
    CHECK_EQ(StickyEmbeddedBlob(), Isolate::CurrentEmbeddedBlob());
  
    InstructionStream::FreeOffHeapInstructionStream(
        const_cast<uint8_t*>(Isolate::CurrentEmbeddedBlob()),
        Isolate::CurrentEmbeddedBlobSize());
  
    current_embedded_blob_.store(nullptr, std::memory_order_relaxed);
    current_embedded_blob_size_.store(0, std::memory_order_relaxed);
    sticky_embedded_blob_ = nullptr;
    sticky_embedded_blob_size_ = 0;
  }
  
  void Isolate::SetEmbeddedBlob(const uint8_t* blob, uint32_t blob_size) {
    CHECK_NOT_NULL(blob);
  
    embedded_blob_ = blob;
    embedded_blob_size_ = blob_size;
    current_embedded_blob_.store(blob, std::memory_order_relaxed);
    current_embedded_blob_size_.store(blob_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();
    CHECK_EQ(d.Hash(), d.CreateHash());
  #endif  // DEBUG
  }
  
  void Isolate::ClearEmbeddedBlob() {
    CHECK(enable_embedded_blob_refcounting_);
    CHECK_EQ(embedded_blob_, CurrentEmbeddedBlob());
    CHECK_EQ(embedded_blob_, StickyEmbeddedBlob());
  
    embedded_blob_ = nullptr;
    embedded_blob_size_ = 0;
    current_embedded_blob_.store(nullptr, std::memory_order_relaxed);
    current_embedded_blob_size_.store(0, std::memory_order_relaxed);
    sticky_embedded_blob_ = nullptr;
    sticky_embedded_blob_size_ = 0;
  }
  
  const uint8_t* Isolate::embedded_blob() const { return embedded_blob_; }
  uint32_t Isolate::embedded_blob_size() const { return embedded_blob_size_; }
  
  // static
  const uint8_t* Isolate::CurrentEmbeddedBlob() {
    return current_embedded_blob_.load(std::memory_order::memory_order_relaxed);
  }
  
  // static
  uint32_t Isolate::CurrentEmbeddedBlobSize() {
    return current_embedded_blob_size_.load(
        std::memory_order::memory_order_relaxed);
  }
  
  void ThreadLocalTop::Initialize(Isolate* isolate) {
    *this = ThreadLocalTop();
    isolate_ = isolate;
  #ifdef USE_SIMULATOR
    simulator_ = Simulator::current(isolate);
  #endif
    thread_id_ = ThreadId::Current();
    thread_in_wasm_flag_address_ = reinterpret_cast<Address>(
        trap_handler::GetThreadInWasmThreadLocalAddress());
  }
  
  void ThreadLocalTop::Free() {
    // Match unmatched PopPromise calls.
    while (promise_on_stack_) isolate_->PopPromise();
  }
  
  
  base::Thread::LocalStorageKey Isolate::isolate_key_;
  base::Thread::LocalStorageKey Isolate::per_isolate_thread_data_key_;
  base::Atomic32 Isolate::isolate_counter_ = 0;
  #if DEBUG
  base::Atomic32 Isolate::isolate_key_created_ = 0;
  #endif
  
  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) {
        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(!thread_manager_->mutex_owner_.Equals(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
    base::Relaxed_Store(&isolate_key_created_, 1);
  #endif
    per_isolate_thread_data_key_ = base::Thread::CreateThreadLocalKey();
    init_memcopy_functions();
  }
  
  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::kTop, nullptr,
                        FullObjectSlot(&thread->pending_exception_));
    v->VisitRootPointer(Root::kTop, nullptr,
                        FullObjectSlot(&thread->pending_message_obj_));
    v->VisitRootPointer(Root::kTop, nullptr, FullObjectSlot(&thread->context_));
    v->VisitRootPointer(Root::kTop, 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::kTop, nullptr,
          FullObjectSlot(reinterpret_cast<Address>(&(block->exception_))));
      v->VisitRootPointer(
          Root::kTop, nullptr,
          FullObjectSlot(reinterpret_cast<Address>(&(block->message_obj_))));
    }
  
    // Iterate over pointers on native execution stack.
    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::IterateDeferredHandles(RootVisitor* visitor) {
    for (DeferredHandles* deferred = deferred_handles_head_; deferred != nullptr;
         deferred = deferred->next_) {
      deferred->Iterate(visitor);
    }
  }
  
  
  #ifdef DEBUG
  bool Isolate::IsDeferredHandle(Address* handle) {
    // Comparing unrelated pointers (not from the same array) is undefined
    // behavior, so cast to Address before making arbitrary comparisons.
    Address handle_as_address = reinterpret_cast<Address>(handle);
    // Each DeferredHandles instance keeps the handles to one job in the
    // concurrent recompilation queue, containing a list of blocks.  Each block
    // contains kHandleBlockSize handles except for the first block, which may
    // not be fully filled.
    // We iterate through all the blocks to see whether the argument handle
    // belongs to one of the blocks.  If so, it is deferred.
    for (DeferredHandles* deferred = deferred_handles_head_; deferred != nullptr;
         deferred = deferred->next_) {
      std::vector<Address*>* blocks = &deferred->blocks_;
      for (size_t i = 0; i < blocks->size(); i++) {
        Address* block_limit = (i == 0) ? deferred->first_block_limit_
                                        : blocks->at(i) + kHandleBlockSize;
        if (reinterpret_cast<Address>(blocks->at(i)) <= handle_as_address &&
            handle_as_address < reinterpret_cast<Address>(block_limit)) {
          return true;
        }
      }
    }
    return false;
  }
  #endif  // DEBUG
  
  
  void Isolate::RegisterTryCatchHandler(v8::TryCatch* that) {
    thread_local_top()->set_try_catch_handler(that);
  }
  
  
  void Isolate::UnregisterTryCatchHandler(v8::TryCatch* that) {
    DCHECK(thread_local_top()->try_catch_handler() == that);
    thread_local_top()->set_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()) {
      if (it.frame()->type() == StackFrame::INTERNAL) continue;
      code_objects_[i++] =
          reinterpret_cast<void*>(it.frame()->unchecked_code().ptr());
    }
  }
  
  namespace {
  
  class FrameArrayBuilder {
   public:
    FrameArrayBuilder(Isolate* isolate, FrameSkipMode mode, int limit,
                      Handle<Object> caller)
        : isolate_(isolate), mode_(mode), limit_(limit), caller_(caller) {
      switch (mode_) {
        case SKIP_FIRST:
          skip_next_frame_ = true;
          break;
        case SKIP_UNTIL_SEEN:
          DCHECK(caller_->IsJSFunction());
          skip_next_frame_ = true;
          break;
        case SKIP_NONE:
          skip_next_frame_ = false;
          break;
      }
  
      elements_ = isolate->factory()->NewFrameArray(Min(limit, 10));
    }
  
    void AppendAsyncFrame(Handle<JSGeneratorObject> generator_object) {
      if (full()) return;
      Handle<JSFunction> function(generator_object->function(), isolate_);
      if (!IsVisibleInStackTrace(function)) return;
      int flags = FrameArray::kIsAsync;
      if (IsStrictFrame(function)) flags |= FrameArray::kIsStrict;
  
      Handle<Object> receiver(generator_object->receiver(), isolate_);
      Handle<AbstractCode> code(
          AbstractCode::cast(function->shared()->GetBytecodeArray()), isolate_);
      int offset = Smi::ToInt(generator_object->input_or_debug_pos());
      // The stored bytecode offset is relative to a different base than what
      // is used in the source position table, hence the subtraction.
      offset -= BytecodeArray::kHeaderSize - kHeapObjectTag;
      elements_ = FrameArray::AppendJSFrame(elements_, receiver, function, code,
                                            offset, flags);
    }
  
    void AppendPromiseAllFrame(Handle<Context> context, int offset) {
      if (full()) return;
      int flags = FrameArray::kIsAsync | FrameArray::kIsPromiseAll;
  
      Handle<Context> native_context(context->native_context(), isolate_);
      Handle<JSFunction> function(native_context->promise_all(), isolate_);
      if (!IsVisibleInStackTrace(function)) return;
  
      Handle<Object> receiver(native_context->promise_function(), isolate_);
      Handle<AbstractCode> code(AbstractCode::cast(function->code()), isolate_);
      elements_ = FrameArray::AppendJSFrame(elements_, receiver, function, code,
                                            offset, flags);
    }
  
    void AppendJavaScriptFrame(
        FrameSummary::JavaScriptFrameSummary const& summary) {
      // Filter out internal frames that we do not want to show.
      if (!IsVisibleInStackTrace(summary.function())) return;
  
      Handle<AbstractCode> abstract_code = summary.abstract_code();
      const int offset = summary.code_offset();
  
      const bool is_constructor = summary.is_constructor();
  
      int flags = 0;
      Handle<JSFunction> function = summary.function();
      if (IsStrictFrame(function)) flags |= FrameArray::kIsStrict;
      if (is_constructor) flags |= FrameArray::kIsConstructor;
  
      elements_ = FrameArray::AppendJSFrame(
          elements_, TheHoleToUndefined(isolate_, summary.receiver()), function,
          abstract_code, offset, flags);
    }
  
    void AppendWasmCompiledFrame(
        FrameSummary::WasmCompiledFrameSummary const& summary) {
      if (summary.code()->kind() != wasm::WasmCode::kFunction) return;
      Handle<WasmInstanceObject> instance = summary.wasm_instance();
      int flags = 0;
      if (instance->module_object()->is_asm_js()) {
        flags |= FrameArray::kIsAsmJsWasmFrame;
        if (summary.at_to_number_conversion()) {
          flags |= FrameArray::kAsmJsAtNumberConversion;
        }
      } else {
        flags |= FrameArray::kIsWasmFrame;
      }
  
      elements_ = FrameArray::AppendWasmFrame(
          elements_, instance, summary.function_index(), summary.code(),
          summary.code_offset(), flags);
    }
  
    void AppendWasmInterpretedFrame(
        FrameSummary::WasmInterpretedFrameSummary const& summary) {
      Handle<WasmInstanceObject> instance = summary.wasm_instance();
      int flags = FrameArray::kIsWasmInterpretedFrame;
      DCHECK(!instance->module_object()->is_asm_js());
      elements_ = FrameArray::AppendWasmFrame(elements_, instance,
                                              summary.function_index(), {},
                                              summary.byte_offset(), flags);
    }
  
    void AppendBuiltinExitFrame(BuiltinExitFrame* exit_frame) {
      Handle<JSFunction> function = handle(exit_frame->function(), isolate_);
  
      // Filter out internal frames that we do not want to show.
      if (!IsVisibleInStackTrace(function)) return;
  
      Handle<Object> receiver(exit_frame->receiver(), isolate_);
      Handle<Code> code(exit_frame->LookupCode(), isolate_);
      const int offset =
          static_cast<int>(exit_frame->pc() - code->InstructionStart());
  
      int flags = 0;
      if (IsStrictFrame(function)) flags |= FrameArray::kIsStrict;
      if (exit_frame->IsConstructor()) flags |= FrameArray::kIsConstructor;
  
      elements_ = FrameArray::AppendJSFrame(elements_, receiver, function,
                                            Handle<AbstractCode>::cast(code),
                                            offset, flags);
    }
  
    bool full() { return elements_->FrameCount() >= limit_; }
  
    Handle<FrameArray> GetElements() {
      elements_->ShrinkToFit(isolate_);
      return elements_;
    }
  
   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();
      }
      return true;
    }
  
    bool IsInSameSecurityContext(Handle<JSFunction> function) {
      return isolate_->context()->HasSameSecurityTokenAs(function->context());
    }
  
    // TODO(jgruber): Fix all cases in which frames give us a hole value (e.g. the
    // receiver in RegExp constructor frames.
    Handle<Object> TheHoleToUndefined(Isolate* isolate, Handle<Object> in) {
      return (in->IsTheHole(isolate))
                 ? Handle<Object>::cast(isolate->factory()->undefined_value())
                 : in;
    }
  
    Isolate* isolate_;
    const FrameSkipMode mode_;
    int limit_;
    const Handle<Object> caller_;
    bool skip_next_frame_ = true;
    bool encountered_strict_function_ = false;
    Handle<FrameArray> 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 = 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; }
  
  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,
                              FrameArrayBuilder* 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);
  
        // We store the offset of the promise into the {function}'s
        // hash field for promise resolve element callbacks.
        int const offset = Smi::ToInt(Smi::cast(function->GetIdentityHash())) - 1;
        builder->AppendPromiseAllFrame(context, offset);
  
        // 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 {
        // 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;
        }
      }
    }
  }
  
  }  // namespace
  
  Handle<Object> Isolate::CaptureSimpleStackTrace(Handle<JSReceiver> error_object,
                                                  FrameSkipMode mode,
                                                  Handle<Object> caller) {
    DisallowJavascriptExecution no_js(this);
  
    int limit;
    if (!GetStackTraceLimit(this, &limit)) return factory()->undefined_value();
  
    FrameArrayBuilder builder(this, mode, limit, caller);
  
    // 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(this); !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::BUILTIN:
        case StackFrame::WASM_COMPILED:
        case StackFrame::WASM_INTERPRETER_ENTRY: {
          // A standard frame may include many summarized frames (due to
          // inlining).
          std::vector<FrameSummary> frames;
          StandardFrame::cast(frame)->Summarize(&frames);
          for (size_t i = frames.size(); i-- != 0 && !builder.full();) {
            const auto& summary = frames[i];
            if (summary.IsJavaScript()) {
              //=========================================================
              // Handle a JavaScript frame.
              //=========================================================
              auto const& java_script = summary.AsJavaScript();
              builder.AppendJavaScriptFrame(java_script);
            } else if (summary.IsWasmCompiled()) {
              //=========================================================
              // Handle a WASM compiled frame.
              //=========================================================
              auto const& wasm_compiled = summary.AsWasmCompiled();
              builder.AppendWasmCompiledFrame(wasm_compiled);
            } else if (summary.IsWasmInterpreted()) {
              //=========================================================
              // Handle a WASM interpreted frame.
              //=========================================================
              auto const& wasm_interpreted = summary.AsWasmInterpreted();
              builder.AppendWasmInterpretedFrame(wasm_interpreted);
            }
          }
          break;
        }
  
        case StackFrame::BUILTIN_EXIT:
          // 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 (FLAG_async_stack_traces) {
      Handle<Object> current_microtask = 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(this, promise_reaction_job_task->handler(),
                              Builtins::kAsyncFunctionAwaitResolveClosure) ||
            IsBuiltinFunction(this, promise_reaction_job_task->handler(),
                              Builtins::kAsyncGeneratorAwaitResolveClosure) ||
            IsBuiltinFunction(this, promise_reaction_job_task->handler(),
                              Builtins::kAsyncGeneratorYieldResolveClosure)) {
          // 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(),
              this);
          Handle<JSGeneratorObject> generator_object(
              JSGeneratorObject::cast(context->extension()), this);
          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(), this);
              CaptureAsyncStackTrace(this, promise, &builder);
            } else {
              Handle<JSAsyncGeneratorObject> async_generator_object =
                  Handle<JSAsyncGeneratorObject>::cast(generator_object);
              Handle<AsyncGeneratorRequest> async_generator_request(
                  AsyncGeneratorRequest::cast(async_generator_object->queue()),
                  this);
              Handle<JSPromise> promise(
                  JSPromise::cast(async_generator_request->promise()), this);
              CaptureAsyncStackTrace(this, 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(), this);
          if (promise_or_capability->IsJSPromise()) {
            Handle<JSPromise> promise =
                Handle<JSPromise>::cast(promise_or_capability);
            CaptureAsyncStackTrace(this, promise, &builder);
          }
        }
      }
    }
  
    // TODO(yangguo): Queue this structured stack trace for preprocessing on GC.
    return factory()->NewJSArrayWithElements(builder.GetElements());
  }
  
  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, LanguageMode::kStrict),
                          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,
                                            LanguageMode::kStrict),
                        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());
    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_interpreted()) {
      InterpretedFrame* iframe = static_cast<InterpretedFrame*>(frame);
      Address bytecode_start =
          iframe->GetBytecodeArray()->GetFirstBytecodeAddress();
      return bytecode_start + iframe->GetBytecodeOffset();
    }
  
    return frame->pc();
  }
  
  class CaptureStackTraceHelper {
   public:
    explicit CaptureStackTraceHelper(Isolate* isolate) : isolate_(isolate) {}
  
    Handle<StackFrameInfo> NewStackFrameObject(FrameSummary& summ) {
      if (summ.IsJavaScript()) return NewStackFrameObject(summ.AsJavaScript());
      if (summ.IsWasm()) return NewStackFrameObject(summ.AsWasm());
      UNREACHABLE();
    }
  
    Handle<StackFrameInfo> NewStackFrameObject(
        const FrameSummary::JavaScriptFrameSummary& summ) {
      int code_offset;
      Handle<ByteArray> source_position_table;
      Handle<Object> maybe_cache;
      Handle<SimpleNumberDictionary> cache;
      if (!FLAG_optimize_for_size) {
        code_offset = summ.code_offset();
        source_position_table =
            handle(summ.abstract_code()->source_position_table(), isolate_);
        maybe_cache = handle(summ.abstract_code()->stack_frame_cache(), isolate_);
        if (maybe_cache->IsSimpleNumberDictionary()) {
          cache = Handle<SimpleNumberDictionary>::cast(maybe_cache);
        } else {
          cache = SimpleNumberDictionary::New(isolate_, 1);
        }
        int entry = cache->FindEntry(isolate_, code_offset);
        if (entry != NumberDictionary::kNotFound) {
          Handle<StackFrameInfo> frame(
              StackFrameInfo::cast(cache->ValueAt(entry)), isolate_);
          return frame;
        }
      }
  
      Handle<StackFrameInfo> frame = factory()->NewStackFrameInfo();
      Handle<Script> script = Handle<Script>::cast(summ.script());
      Script::PositionInfo info;
      bool valid_pos = Script::GetPositionInfo(script, summ.SourcePosition(),
                                               &info, Script::WITH_OFFSET);
      if (valid_pos) {
        frame->set_line_number(info.line + 1);
        frame->set_column_number(info.column + 1);
      }
      frame->set_script_id(script->id());
      frame->set_script_name(script->name());
      frame->set_script_name_or_source_url(script->GetNameOrSourceURL());
      frame->set_is_eval(script->compilation_type() ==
                         Script::COMPILATION_TYPE_EVAL);
      Handle<String> function_name = summ.FunctionName();
      frame->set_function_name(*function_name);
      frame->set_is_constructor(summ.is_constructor());
      frame->set_is_wasm(false);
      if (!FLAG_optimize_for_size) {
        auto new_cache =
            SimpleNumberDictionary::Set(isolate_, cache, code_offset, frame);
        if (*new_cache != *cache || !maybe_cache->IsNumberDictionary()) {
          AbstractCode::SetStackFrameCache(summ.abstract_code(), new_cache);
        }
      }
      frame->set_id(next_id());
      return frame;
    }
  
    Handle<StackFrameInfo> NewStackFrameObject(
        const FrameSummary::WasmFrameSummary& summ) {
      Handle<StackFrameInfo> info = factory()->NewStackFrameInfo();
  
      Handle<WasmModuleObject> module_object(
          summ.wasm_instance()->module_object(), isolate_);
      Handle<String> name = WasmModuleObject::GetFunctionName(
          isolate_, module_object, summ.function_index());
      info->set_function_name(*name);
      // Encode the function index as line number (1-based).
      info->set_line_number(summ.function_index() + 1);
      // Encode the byte offset as column (1-based).
      int position = summ.byte_offset();
      // Make position 1-based.
      if (position >= 0) ++position;
      info->set_column_number(position);
      info->set_script_id(summ.script()->id());
      info->set_is_wasm(true);
      info->set_id(next_id());
      return info;
    }
  
   private:
    inline Factory* factory() { return isolate_->factory(); }
  
    int next_id() const {
      int id = isolate_->last_stack_frame_info_id() + 1;
      isolate_->set_last_stack_frame_info_id(id);
      return id;
    }
  
    Isolate* isolate_;
  };
  
  Handle<FixedArray> Isolate::CaptureCurrentStackTrace(
      int frame_limit, StackTrace::StackTraceOptions options) {
    DisallowJavascriptExecution no_js(this);
    CaptureStackTraceHelper helper(this);
  
    // Ensure no negative values.
    int limit = Max(frame_limit, 0);
    Handle<FixedArray> stack_trace_elems = factory()->NewFixedArray(limit);
  
    int frames_seen = 0;
    for (StackTraceFrameIterator it(this); !it.done() && (frames_seen < limit);
         it.Advance()) {
      StandardFrame* frame = it.frame();
      // Set initial size to the maximum inlining level + 1 for the outermost
      // function.
      std::vector<FrameSummary> frames;
      frame->Summarize(&frames);
      for (size_t i = frames.size(); i != 0 && frames_seen < limit; i--) {
        FrameSummary& frame = frames[i - 1];
        if (!frame.is_subject_to_debugging()) continue;
        // Filter frames from other security contexts.
        if (!(options & StackTrace::kExposeFramesAcrossSecurityOrigins) &&
            !this->context()->HasSameSecurityTokenAs(*frame.native_context()))
          continue;
        Handle<StackFrameInfo> new_frame_obj = helper.NewStackFrameObject(frame);
        stack_trace_elems->set(frames_seen, *new_frame_obj);
        frames_seen++;
      }
    }
    return FixedArray::ShrinkOrEmpty(this, stack_trace_elems, frames_seen);
  }
  
  
  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) {
    // The MentionedObjectCache is not GC-proof at the moment.
    DisallowHeapAllocation no_gc;
    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;
    { DisallowHeapAllocation no_gc;
      AccessCheckInfo access_check_info = AccessCheckInfo::Get(this, receiver);
      if (access_check_info.is_null()) {
        AllowHeapAllocation doesnt_matter_anymore;
        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;
    {
      DisallowHeapAllocation 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;
    { DisallowHeapAllocation 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_abort_on_stack_or_string_length_overflow) {
      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> no_caller;
    Handle<Object> exception;
    ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
        this, exception,
        ErrorUtils::Construct(this, fun, fun, msg, SKIP_NONE, no_caller, true));
  
    Throw(*exception, nullptr);
  
  #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::TerminateExecution() {
    return Throw(ReadOnlyRoots(this).termination_exception(), nullptr);
  }
  
  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() {
    RuntimeCallTimerScope runtimeTimer(
        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);
    }
  }
  
  
  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
  }
  
  Object Isolate::Throw(Object raw_exception, MessageLocation* location) {
    DCHECK(!has_pending_exception());
  
    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 (AllowHeapAllocation::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)) {
      debug()->OnThrow(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 = CreateMessage(exception, location);
        thread_local_top()->pending_message_obj_ = *message_obj;
  
        // For any exception not caught by JavaScript, even when an external
        // handler is present:
        // 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();
          }
        }
      }
    }
  
    // 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();
  }
  
  Object Isolate::UnwindAndFindHandler() {
    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.
      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(),
                              table.LookupReturn(0), code->constant_pool(),
                              handler->address() + StackHandlerConstants::kSize,
                              0);
        }
  
        case StackFrame::WASM_COMPILED: {
          if (trap_handler::IsThreadInWasm()) {
            trap_handler::ClearThreadInWasm();
          }
  
          // For WebAssembly frames we perform a lookup in the handler table.
          if (!catchable_by_js) break;
          WasmCompiledFrame* wasm_frame = static_cast<WasmCompiledFrame*>(frame);
          int stack_slots = 0;  // Will contain stack slot count of frame.
          int offset = wasm_frame->LookupExceptionHandlerInTable(&stack_slots);
          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 -
                              stack_slots * kPointerSize;
  
          // This is going to be handled by Wasm, so we need to set the TLS flag
          // again. It was cleared above assuming the frame would be unwound.
          trap_handler::SetThreadInWasm();
  
          // Gather information from the frame.
          wasm::WasmCode* wasm_code =
              wasm_engine()->code_manager()->LookupCode(frame->pc());
          return FoundHandler(Context(), wasm_code->instruction_start(), offset,
                              wasm_code->constant_pool(), return_sp, frame->fp());
        }
  
        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);
          int stack_slots = 0;  // Will contain stack slot count of frame.
          int offset =
              js_frame->LookupExceptionHandlerInTable(&stack_slots, 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 -
                              stack_slots * kPointerSize;
  
          // Gather information from the frame.
          Code code = frame->LookupCode();
  
          // TODO(bmeurer): Turbofanned BUILTIN frames appear as OPTIMIZED,
          // but do not have a code kind of OPTIMIZED_FUNCTION.
          if (code->kind() == Code::OPTIMIZED_FUNCTION &&
              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(), 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);
          Code code = stub_frame->LookupCode();
          if (!code->IsCode() || code->kind() != Code::BUILTIN ||
              !code->handler_table_offset() || !code->is_turbofanned()) {
            break;
          }
  
          int stack_slots = 0;  // Will contain stack slot count of frame.
          int offset = stub_frame->LookupExceptionHandlerInTable(&stack_slots);
          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 -
                              stack_slots * kPointerSize;
  
          return FoundHandler(Context(), code->InstructionStart(), offset,
                              code->constant_pool(), return_sp, frame->fp());
        }
  
        case StackFrame::INTERPRETED: {
          // For interpreted frame we perform a range lookup in the handler table.
          if (!catchable_by_js) break;
          InterpretedFrame* js_frame = static_cast<InterpretedFrame*>(frame);
          int register_slots = InterpreterFrameConstants::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 * kPointerSize;
  
          // 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));
          js_frame->PatchBytecodeOffset(static_cast<int>(offset));
  
          Code code =
              builtins()->builtin(Builtins::kInterpreterEnterBytecodeDispatch);
          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,
                     JavaScriptFrame::cast(frame)->LookupExceptionHandlerInTable(
                         nullptr, nullptr));
          }
          break;
  
        case StackFrame::WASM_INTERPRETER_ENTRY: {
          if (trap_handler::IsThreadInWasm()) {
            trap_handler::ClearThreadInWasm();
          }
          WasmInterpreterEntryFrame* interpreter_frame =
              WasmInterpreterEntryFrame::cast(frame);
          // TODO(wasm): Implement try-catch in the interpreter.
          interpreter_frame->debug_info()->Unwind(frame->fp());
        } 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() == AbstractCode::BUILTIN) {
            prediction = code->GetCode()->GetBuiltinCatchPrediction();
            if (prediction == HandlerTable::UNCAUGHT) continue;
            return prediction;
          }
  
          // Must have been constructed from a bytecode array.
          CHECK_EQ(AbstractCode::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::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::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() != Code::BUILTIN ||
              !code->handler_table_offset() || !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 (handle_scope_implementer()->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) {
    for (StackTraceFrameIterator it(this); !it.done(); it.Advance()) {
      if (!it.is_javascript()) continue;
  
      HandleScope scope(this);
      JavaScriptFrame* frame = it.javascript_frame();
  
      Handle<Object> receiver(frame->receiver(), this);
      Handle<JSFunction> function(frame->function(), this);
      Handle<AbstractCode> code;
      int offset;
      if (frame->is_interpreted()) {
        InterpretedFrame* interpreted_frame = InterpretedFrame::cast(frame);
        code = handle(AbstractCode::cast(interpreted_frame->GetBytecodeArray()),
                      this);
        offset = interpreted_frame->GetBytecodeOffset();
      } else {
        code = handle(AbstractCode::cast(frame->LookupCode()), this);
        offset = static_cast<int>(frame->pc() - code->InstructionStart());
      }
  
      JSStackFrame site(this, receiver, function, code, offset);
      Handle<String> line = site.ToString().ToHandleChecked();
      if (line->length() > 0) {
        line->PrintOn(out);
        PrintF(out, "\n");
      }
    }
  }
  
  bool Isolate::ComputeLocation(MessageLocation* target) {
    StackTraceFrameIterator it(this);
    if (it.done()) return false;
    StandardFrame* 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;
    frame->Summarize(&frames);
    FrameSummary& summary = frames.back();
    int pos = summary.SourcePosition();
    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);
    }
    *target = MessageLocation(Handle<Script>::cast(script), pos, pos + 1, shared);
    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->IsJSArray()) return false;
    Handle<JSArray> simple_stack_trace = Handle<JSArray>::cast(property);
  
    Handle<FrameArray> elements(FrameArray::cast(simple_stack_trace->elements()),
                                this);
  
    const int frame_count = elements->FrameCount();
    for (int i = 0; i < frame_count; i++) {
      if (elements->IsWasmFrame(i) || elements->IsAsmJsWasmFrame(i)) {
        Handle<WasmInstanceObject> instance(elements->WasmInstance(i), this);
        uint32_t func_index =
            static_cast<uint32_t>(elements->WasmFunctionIndex(i)->value());
        wasm::WasmCode* wasm_code = reinterpret_cast<wasm::WasmCode*>(
            elements->WasmCodeObject(i)->foreign_address());
        int code_offset = elements->Offset(i)->value();
        bool is_at_number_conversion =
            elements->IsAsmJsWasmFrame(i) &&
            elements->Flags(i)->value() & FrameArray::kAsmJsAtNumberConversion;
        int byte_offset =
            FrameSummary::WasmCompiledFrameSummary::GetWasmSourcePosition(
                wasm_code, code_offset);
        int pos = WasmModuleObject::GetSourcePosition(
            handle(instance->module_object(), this), func_index, byte_offset,
            is_at_number_conversion);
        Handle<Script> script(instance->module_object()->script(), this);
  
        *target = MessageLocation(script, pos, pos + 1);
        return true;
      }
  
      Handle<JSFunction> fun = handle(elements->Function(i), this);
      if (!fun->shared()->IsSubjectToDebugging()) continue;
  
      Object script = fun->shared()->script();
      if (script->IsScript() &&
          !(Script::cast(script)->source()->IsUndefined(this))) {
        AbstractCode abstract_code = elements->Code(i);
        const int code_offset = elements->Offset(i)->value();
        const int pos = abstract_code->SourcePosition(code_offset);
  
        Handle<Script> casted_script(Script::cast(script), this);
        *target = MessageLocation(casted_script, pos, pos + 1);
        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);
  }
  
  void Isolate::ReportPendingMessagesImpl(bool report_externally) {
    Object exception = pending_exception();
  
    // 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)) 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 (report_externally) {
      // 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);
    }
  
    // 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<Script> script(message->script(), this);
      int start_pos = message->start_position();
      int end_pos = message->end_position();
      MessageLocation location(script, start_pos, end_pos);
      MessageHandler::ReportMessage(this, &location, message);
    }
  }
  
  void Isolate::ReportPendingMessages() {
    DCHECK(AllowExceptions::IsAllowed(this));
  
    // The embedder might run script in response to an exception.
    AllowJavascriptExecutionDebugOnly allow_script(this);
  
    Object exception = 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;
  
    ReportPendingMessagesImpl(IsExternalHandlerOnTop(exception));
  }
  
  void Isolate::ReportPendingMessagesFromJavaScript() {
    DCHECK(AllowExceptions::IsAllowed(this));
  
    auto IsHandledByJavaScript = [=]() {
      // In this situation, the exception is always a non-terminating exception.
  
      // Get the top-most JS_ENTRY handler, cannot be on top if it doesn't exist.
      Address entry_handler = Isolate::handler(thread_local_top());
      DCHECK_NE(entry_handler, kNullAddress);
      entry_handler = StackHandler::FromAddress(entry_handler)->next_address();
  
      // 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;
  
      return (entry_handler < external_handler);
    };
  
    auto IsHandledExternally = [=]() {
      Address external_handler = thread_local_top()->try_catch_handler_address();
      if (external_handler == kNullAddress) 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());
      DCHECK_NE(entry_handler, kNullAddress);
      entry_handler = StackHandler::FromAddress(entry_handler)->next_address();
      return (entry_handler > external_handler);
    };
  
    auto PropagateToExternalHandler = [=]() {
      if (IsHandledByJavaScript()) {
        thread_local_top_.external_caught_exception_ = false;
        return false;
      }
  
      if (!IsHandledExternally()) {
        thread_local_top_.external_caught_exception_ = false;
        return true;
      }
  
      thread_local_top_.external_caught_exception_ = true;
      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;
    };
  
    // Try to propagate to an external v8::TryCatch handler.
    if (!PropagateToExternalHandler()) return;
  
    ReportPendingMessagesImpl(true);
  }
  
  MessageLocation Isolate::GetMessageLocation() {
    DCHECK(has_pending_exception());
  
    if (thread_local_top_.pending_exception_ !=
            ReadOnlyRoots(heap()).termination_exception() &&
        !thread_local_top_.pending_message_obj_->IsTheHole(this)) {
      Handle<JSMessageObject> message_obj(
          JSMessageObject::cast(thread_local_top_.pending_message_obj_), this);
      Handle<Script> script(message_obj->script(), this);
      int start_pos = message_obj->start_position();
      int end_pos = message_obj->end_position();
      return MessageLocation(script, start_pos, end_pos);
    }
  
    return MessageLocation();
  }
  
  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 InternalPromiseHasUserDefinedRejectHandler(Isolate* isolate,
                                                  Handle<JSPromise> promise);
  
  bool PromiseHandlerCheck(Isolate* isolate, Handle<JSReceiver> handler,
                           Handle<JSReceiver> deferred_promise) {
    // Recurse to the forwarding Promise, if any. This may be 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);
    if (forwarding_handler->IsUndefined(isolate)) {
      return true;
    }
  
    if (!deferred_promise->IsJSPromise()) {
      return true;
    }
  
    return InternalPromiseHasUserDefinedRejectHandler(
        isolate, Handle<JSPromise>::cast(deferred_promise));
  }
  
  bool InternalPromiseHasUserDefinedRejectHandler(Isolate* isolate,
                                                  Handle<JSPromise> promise) {
    // 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 this Promise is subsumed by another Promise (a Promise resolved
    // with another Promise, or an intermediate, hidden, throwaway Promise
    // within async/await), then recurse on the outer Promise.
    // In this case, the dependency is one possible way that the Promise
    // could be resolved, so it does not subsume the other following cases.
    Handle<Symbol> key = isolate->factory()->promise_handled_by_symbol();
    Handle<Object> outer_promise_obj = JSObject::GetDataProperty(promise, key);
    if (outer_promise_obj->IsJSPromise() &&
        InternalPromiseHasUserDefinedRejectHandler(
            isolate, Handle<JSPromise>::cast(outer_promise_obj))) {
      return true;
    }
  
    if (promise->status() == Promise::kPending) {
      for (Handle<Object> current(promise->reactions(), isolate);
           !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)) {
          Handle<JSPromise> promise = Handle<JSPromise>::cast(
              promise_or_capability->IsJSPromise()
                  ? promise_or_capability
                  : handle(Handle<PromiseCapability>::cast(promise_or_capability)
                               ->promise(),
                           isolate));
          if (reaction->reject_handler()->IsUndefined(isolate)) {
            if (InternalPromiseHasUserDefinedRejectHandler(isolate, promise)) {
              return true;
            }
          } else {
            Handle<JSReceiver> current_handler(
                JSReceiver::cast(reaction->reject_handler()), isolate);
            if (PromiseHandlerCheck(isolate, current_handler, promise)) {
              return true;
            }
          }
        }
        current = handle(reaction->next(), isolate);
      }
    }
  
    return false;
  }
  
  }  // namespace
  
  bool Isolate::PromiseHasUserDefinedRejectHandler(Handle<Object> promise) {
    if (!promise->IsJSPromise()) return false;
    return InternalPromiseHasUserDefinedRejectHandler(
        this, Handle<JSPromise>::cast(promise));
  }
  
  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() != Code::BUILTIN ||
            !code->handler_table_offset() || !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::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 (PromiseHasUserDefinedRejectHandler(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;
  }
  
  
  void Isolate::SetAbortOnUncaughtExceptionCallback(
      v8::Isolate::AbortOnUncaughtExceptionCallback callback) {
    abort_on_uncaught_exception_callback_ = callback;
  }
  
  bool Isolate::AreWasmThreadsEnabled(Handle<Context> context) {
    if (wasm_threads_enabled_callback()) {
      v8::Local<v8::Context> api_context = v8::Utils::ToLocal(context);
      return wasm_threads_enabled_callback()(api_context);
    }
    return FLAG_experimental_wasm_threads;
  }
  
  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));
    InitializeThreadLocal();
    clear_pending_exception();
    clear_pending_message();
    clear_scheduled_exception();
    return to + sizeof(ThreadLocalTop);
  }
  
  
  char* Isolate::RestoreThread(char* from) {
    MemCopy(reinterpret_cast<char*>(thread_local_top()), from,
            sizeof(ThreadLocalTop));
  // This might be just paranoia, but it seems to be needed in case a
  // thread_local_top_ is restored on a separate OS thread.
  #ifdef USE_SIMULATOR
    thread_local_top()->simulator_ = Simulator::current(this);
  #endif
    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;
      }
    }
  }
  
  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;
  }
  
  void Isolate::SetWasmEngine(std::shared_ptr<wasm::WasmEngine> engine) {
    DCHECK_NULL(wasm_engine_);  // Only call once before {Init}.
    wasm_engine_ = std::move(engine);
    wasm_engine_->AddIsolate(this);
    wasm::WasmCodeManager::InstallSamplingGCCallback(this);
  }
  
  // NOLINTNEXTLINE
  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 VerboseAccountingAllocator : public AccountingAllocator {
   public:
    VerboseAccountingAllocator(Heap* heap, size_t allocation_sample_bytes,
                               size_t pool_sample_bytes)
        : heap_(heap),
          last_memory_usage_(0),
          last_pool_size_(0),
          nesting_deepth_(0),
          allocation_sample_bytes_(allocation_sample_bytes),
          pool_sample_bytes_(pool_sample_bytes) {}
  
    v8::internal::Segment* GetSegment(size_t size) override {
      v8::internal::Segment* memory = AccountingAllocator::GetSegment(size);
      if (memory) {
        size_t malloced_current = GetCurrentMemoryUsage();
        size_t pooled_current = GetCurrentPoolSize();
  
        if (last_memory_usage_ + allocation_sample_bytes_ < malloced_current ||
            last_pool_size_ + pool_sample_bytes_ < pooled_current) {
          PrintMemoryJSON(malloced_current, pooled_current);
          last_memory_usage_ = malloced_current;
          last_pool_size_ = pooled_current;
        }
      }
      return memory;
    }
  
    void ReturnSegment(v8::internal::Segment* memory) override {
      AccountingAllocator::ReturnSegment(memory);
      size_t malloced_current = GetCurrentMemoryUsage();
      size_t pooled_current = GetCurrentPoolSize();
  
      if (malloced_current + allocation_sample_bytes_ < last_memory_usage_ ||
          pooled_current + pool_sample_bytes_ < last_pool_size_) {
        PrintMemoryJSON(malloced_current, pooled_current);
        last_memory_usage_ = malloced_current;
        last_pool_size_ = pooled_current;
      }
    }
  
    void ZoneCreation(const Zone* zone) override {
      PrintZoneModificationSample(zone, "zonecreation");
      nesting_deepth_++;
    }
  
    void ZoneDestruction(const Zone* zone) override {
      nesting_deepth_--;
      PrintZoneModificationSample(zone, "zonedestruction");
    }
  
   private:
    void PrintZoneModificationSample(const Zone* zone, const char* type) {
      PrintF(
          "{"
          "\"type\": \"%s\", "
          "\"isolate\": \"%p\", "
          "\"time\": %f, "
          "\"ptr\": \"%p\", "
          "\"name\": \"%s\", "
          "\"size\": %" PRIuS
          ","
          "\"nesting\": %zu}\n",
          type, reinterpret_cast<void*>(heap_->isolate()),
          heap_->isolate()->time_millis_since_init(),
          reinterpret_cast<const void*>(zone), zone->name(),
          zone->allocation_size(), nesting_deepth_.load());
    }
  
    void PrintMemoryJSON(size_t malloced, size_t pooled) {
      // Note: Neither isolate, nor heap is locked, so be careful with accesses
      // as the allocator is potentially used on a concurrent thread.
      double time = heap_->isolate()->time_millis_since_init();
      PrintF(
          "{"
          "\"type\": \"zone\", "
          "\"isolate\": \"%p\", "
          "\"time\": %f, "
          "\"allocated\": %" PRIuS
          ","
          "\"pooled\": %" PRIuS "}\n",
          reinterpret_cast<void*>(heap_->isolate()), time, malloced, pooled);
    }
  
    Heap* heap_;
    std::atomic<size_t> last_memory_usage_;
    std::atomic<size_t> last_pool_size_;
    std::atomic<size_t> nesting_deepth_;
    size_t allocation_sample_bytes_, pool_sample_bytes_;
  };
  
  #ifdef DEBUG
  std::atomic<size_t> Isolate::non_disposed_isolates_;
  #endif  // DEBUG
  
  // static
  Isolate* Isolate::New(IsolateAllocationMode mode) {
    // IsolateAllocator allocates the memory for the Isolate object according to
    // the given allocation mode.
    std::unique_ptr<IsolateAllocator> isolate_allocator =
        base::make_unique<IsolateAllocator>(mode);
    // 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_TARGET_ARCH_64_BIT
    DCHECK_IMPLIES(
        mode == IsolateAllocationMode::kInV8Heap,
        IsAligned(isolate->isolate_root(), kPtrComprIsolateRootAlignment));
  #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(base::Relaxed_Load(&isolate_key_created_), 1);
    Isolate* saved_isolate = reinterpret_cast<Isolate*>(
        base::Thread::GetThreadLocal(isolate->isolate_key_));
    SetIsolateThreadLocals(isolate, nullptr);
  
    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);
  }
  
  v8::PageAllocator* Isolate::page_allocator() {
    return isolate_allocator_->page_allocator();
  }
  
  Isolate::Isolate(std::unique_ptr<i::IsolateAllocator> isolate_allocator)
      : isolate_allocator_(std::move(isolate_allocator)),
        id_(base::Relaxed_AtomicIncrement(&isolate_counter_, 1)),
        stack_guard_(this),
        allocator_(FLAG_trace_zone_stats ? new VerboseAccountingAllocator(
                                               &heap_, 256 * KB, 128 * KB)
                                         : new AccountingAllocator()),
        builtins_(this),
        rail_mode_(PERFORMANCE_ANIMATION),
        code_event_dispatcher_(new CodeEventDispatcher()),
        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_.roots_)),
             Internals::kIsolateRootsOffset);
    CHECK_EQ(Internals::kExternalMemoryOffset % 8, 0);
    CHECK_EQ(static_cast<int>(OFFSET_OF(Isolate, isolate_data_.external_memory_)),
             Internals::kExternalMemoryOffset);
    CHECK_EQ(Internals::kExternalMemoryLimitOffset % 8, 0);
    CHECK_EQ(static_cast<int>(
                 OFFSET_OF(Isolate, isolate_data_.external_memory_limit_)),
             Internals::kExternalMemoryLimitOffset);
    CHECK_EQ(Internals::kExternalMemoryAtLastMarkCompactOffset % 8, 0);
    CHECK_EQ(static_cast<int>(OFFSET_OF(
                 Isolate, isolate_data_.external_memory_at_last_mark_compact_)),
             Internals::kExternalMemoryAtLastMarkCompactOffset);
  }
  
  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();
    }
  
    debug()->Unload();
  
    wasm_engine()->DeleteCompileJobsOnIsolate(this);
  
    if (concurrent_recompilation_enabled()) {
      optimizing_compile_dispatcher_->Stop();
      delete optimizing_compile_dispatcher_;
      optimizing_compile_dispatcher_ = nullptr;
    }
  
    heap_.mark_compact_collector()->EnsureSweepingCompleted();
    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();
  
    delete deoptimizer_data_;
    deoptimizer_data_ = nullptr;
    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();
  
    heap_.TearDown();
    logger_->TearDown();
  
    if (wasm_engine_) {
      wasm_engine_->RemoveIsolate(this);
      wasm_engine_.reset();
    }
  
    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;
  
    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 unicode_cache_;
    unicode_cache_ = 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;
  
    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;
  }
  
  void Isolate::InitializeThreadLocal() { thread_local_top_.Initialize(this); }
  
  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());
    DCHECK_NE(0, isolate->embedded_blob_size());
  
    HandleScope scope(isolate);
    Builtins* builtins = isolate->builtins();
  
    EmbeddedData d = EmbeddedData::FromBlob();
  
    for (int i = 0; i < Builtins::builtin_count; i++) {
      if (!Builtins::IsIsolateIndependent(i)) continue;
  
      Address instruction_start = d.InstructionStartOfBuiltin(i);
      Handle<Code> trampoline = isolate->factory()->NewOffHeapTrampolineFor(
          builtins->builtin_handle(i), instruction_start);
  
      // Note that references to the old, on-heap code objects may still exist on
      // the heap. This is fine for the sake of serialization, as serialization
      // will canonicalize all builtins in MaybeCanonicalizeBuiltin().
      //
      // From this point onwards, some builtin code objects may be unreachable and
      // thus collected by the GC.
      builtins->set_builtin(i, *trampoline);
  
      if (isolate->logger()->is_listening_to_code_events() ||
          isolate->is_profiling()) {
        isolate->logger()->LogCodeObject(*trampoline);
      }
    }
  }
  
  }  // namespace
  
  void Isolate::InitializeDefaultEmbeddedBlob() {
    const uint8_t* blob = DefaultEmbeddedBlob();
    uint32_t size = DefaultEmbeddedBlobSize();
  
  #ifdef V8_MULTI_SNAPSHOTS
    if (!FLAG_untrusted_code_mitigations) {
      blob = TrustedEmbeddedBlob();
      size = TrustedEmbeddedBlobSize();
    }
  #endif
  
    if (StickyEmbeddedBlob() != nullptr) {
      base::MutexGuard guard(current_embedded_blob_refcount_mutex_.Pointer());
      // Check again now that we hold the lock.
      if (StickyEmbeddedBlob() != nullptr) {
        blob = StickyEmbeddedBlob();
        size = StickyEmbeddedBlobSize();
        current_embedded_blob_refs_++;
      }
    }
  
    if (blob == nullptr) {
      CHECK_EQ(0, size);
    } else {
      SetEmbeddedBlob(blob, size);
    }
  }
  
  void Isolate::CreateAndSetEmbeddedBlob() {
    base::MutexGuard guard(current_embedded_blob_refcount_mutex_.Pointer());
  
    // If a sticky blob has been set, we reuse it.
    if (StickyEmbeddedBlob() != nullptr) {
      CHECK_EQ(embedded_blob(), StickyEmbeddedBlob());
      CHECK_EQ(CurrentEmbeddedBlob(), StickyEmbeddedBlob());
    } else {
      // Create and set a new embedded blob.
      uint8_t* data;
      uint32_t size;
      InstructionStream::CreateOffHeapInstructionStream(this, &data, &size);
  
      CHECK_EQ(0, current_embedded_blob_refs_);
      const uint8_t* const_data = const_cast<const uint8_t*>(data);
      SetEmbeddedBlob(const_data, size);
      current_embedded_blob_refs_++;
  
      SetStickyEmbeddedBlob(const_data, size);
    }
  
    CreateOffHeapTrampolines(this);
  }
  
  void Isolate::TearDownEmbeddedBlob() {
    // Nothing to do in case the blob is embedded into the binary or unset.
    if (StickyEmbeddedBlob() == nullptr) return;
  
    CHECK_EQ(embedded_blob(), StickyEmbeddedBlob());
    CHECK_EQ(CurrentEmbeddedBlob(), StickyEmbeddedBlob());
  
    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*>(embedded_blob()), embedded_blob_size());
      ClearEmbeddedBlob();
    }
  }
  
  bool Isolate::Init(StartupDeserializer* des) {
    TRACE_ISOLATE(init);
  
    base::ElapsedTimer timer;
    if (des == nullptr && 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(this);
  
    // Safe after setting Heap::isolate_, and initializing StackGuard
    heap_.SetStackLimits();
  
  #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
  
    compilation_cache_ = new CompilationCache(this);
    descriptor_lookup_cache_ = new DescriptorLookupCache();
    unicode_cache_ = new UnicodeCache();
    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);
  
    compiler_dispatcher_ =
        new CompilerDispatcher(this, V8::GetCurrentPlatform(), FLAG_stack_size);
  
    // Enable logging before setting up the heap
    logger_->SetUp(this);
  
    { // NOLINT
      // 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();
  
    isolate_data_.external_reference_table()->Init(this);
  
    // Setup the wasm engine.
    if (wasm_engine_ == nullptr) {
      SetWasmEngine(wasm::WasmEngine::GetWasmEngine());
    }
    DCHECK_NOT_NULL(wasm_engine_);
  
    deoptimizer_data_ = new DeoptimizerData(heap());
  
    const bool create_heap_objects = (des == nullptr);
    if (setup_delegate_ == nullptr) {
      setup_delegate_ = new SetupIsolateDelegate(create_heap_objects);
    }
  
    if (!setup_delegate_->SetupHeap(&heap_)) {
      V8::FatalProcessOutOfMemory(this, "heap object creation");
      return false;
    }
  
    if (create_heap_objects) {
      // Terminate the partial snapshot cache so we can iterate.
      partial_snapshot_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 (FLAG_embedded_builtins && create_heap_objects) {
      builtins_constants_table_builder_ = new BuiltinsConstantsTableBuilder(this);
    }
    setup_delegate_->SetupBuiltins(this);
    if (create_heap_objects) {
      // Create a copy of the the interpreter entry trampoline and store it
      // on the root list. It is used as a template for further copies that
      // may later be created to help profile interpreted code.
      // TODO(jgruber): Merge this with the block below once
      //                FLAG_embedded_builtins is always true.
      HandleScope handle_scope(this);
      Handle<Code> code =
          factory()->CopyCode(BUILTIN_CODE(this, InterpreterEntryTrampoline));
      heap_.SetInterpreterEntryTrampolineForProfiling(*code);
    }
    if (FLAG_embedded_builtins && create_heap_objects) {
      builtins_constants_table_builder_->Finalize();
      delete builtins_constants_table_builder_;
      builtins_constants_table_builder_ = nullptr;
  
      CreateAndSetEmbeddedBlob();
    }
  
    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(this);
      CodeSpaceMemoryModificationScope modification_scope(&heap_);
  
      if (!create_heap_objects) des->DeserializeInto(this);
      load_stub_cache_->Initialize();
      store_stub_cache_->Initialize();
      interpreter_->Initialize();
      heap_.NotifyDeserializationComplete();
    }
    delete setup_delegate_;
    setup_delegate_ = nullptr;
  
    // Initialize the builtin entry table.
    Builtins::UpdateBuiltinEntryTable(this);
  
    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();
  
    // Deserializing may put strange things in the root array's copy of the
    // stack guard.
    heap_.SetStackLimits();
  
    // 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, heap()->HashSeed());
    }
  
    initialized_from_snapshot_ = (des != nullptr);
  
    if (!FLAG_inline_new) heap_.DisableInlineAllocation();
  
    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 (des == nullptr && 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().Equals(
                   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().Equals(
               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);
  }
  
  
  void Isolate::LinkDeferredHandles(DeferredHandles* deferred) {
    deferred->next_ = deferred_handles_head_;
    if (deferred_handles_head_ != nullptr) {
      deferred_handles_head_->previous_ = deferred;
    }
    deferred_handles_head_ = deferred;
  }
  
  
  void Isolate::UnlinkDeferredHandles(DeferredHandles* deferred) {
  #ifdef DEBUG
    // In debug mode assert that the linked list is well-formed.
    DeferredHandles* deferred_iterator = deferred;
    while (deferred_iterator->previous_ != nullptr) {
      deferred_iterator = deferred_iterator->previous_;
    }
    DCHECK(deferred_handles_head_ == deferred_iterator);
  #endif
    if (deferred_handles_head_ == deferred) {
      deferred_handles_head_ = deferred_handles_head_->next_;
    }
    if (deferred->next_ != nullptr) {
      deferred->next_->previous_ = deferred->previous_;
    }
    if (deferred->previous_ != nullptr) {
      deferred->previous_->next_ = deferred->next_;
    }
  }
  
  void Isolate::DumpAndResetStats() {
    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;
    }
    // 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();
    }
    if (V8_UNLIKELY(FLAG_runtime_stats ==
                    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();
    }
  }
  
  void Isolate::AbortConcurrentOptimization(BlockingBehavior behavior) {
    if (concurrent_recompilation_enabled()) {
      DisallowHeapAllocation 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() && !is_block_count_code_coverage();
  }
  
  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_trace_maps;
  }
  
  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;
  
    {
      HeapIterator 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;
  }
  
  bool 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 ||
          current_context->initial_array_prototype() == object ||
          current_context->initial_string_prototype() == object) {
        return true;
      }
      context = current_context->next_context_link();
    }
    return false;
  }
  
  bool Isolate::IsInAnyContext(Object object, uint32_t index) {
    DisallowHeapAllocation 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;
  }
  
  bool Isolate::IsNoElementsProtectorIntact(Context context) {
    PropertyCell no_elements_cell = heap()->no_elements_protector();
    bool cell_reports_intact =
        no_elements_cell->value()->IsSmi() &&
        Smi::ToInt(no_elements_cell->value()) == kProtectorValid;
  
  #ifdef DEBUG
    Context native_context = context->native_context();
  
    Map root_array_map =
        native_context->GetInitialJSArrayMap(GetInitialFastElementsKind());
    JSObject initial_array_proto = JSObject::cast(
        native_context->get(Context::INITIAL_ARRAY_PROTOTYPE_INDEX));
    JSObject initial_object_proto = JSObject::cast(
        native_context->get(Context::INITIAL_OBJECT_PROTOTYPE_INDEX));
    JSObject initial_string_proto = JSObject::cast(
        native_context->get(Context::INITIAL_STRING_PROTOTYPE_INDEX));
  
    if (root_array_map.is_null() || initial_array_proto == initial_object_proto) {
      // We are in the bootstrapping process, and the entire check sequence
      // shouldn't be performed.
      return cell_reports_intact;
    }
  
    // Check that the array prototype hasn't been altered WRT empty elements.
    if (root_array_map->prototype() != initial_array_proto) {
      DCHECK_EQ(false, cell_reports_intact);
      return cell_reports_intact;
    }
  
    FixedArrayBase elements = initial_array_proto->elements();
    ReadOnlyRoots roots(heap());
    if (elements != roots.empty_fixed_array() &&
        elements != roots.empty_slow_element_dictionary()) {
      DCHECK_EQ(false, cell_reports_intact);
      return cell_reports_intact;
    }
  
    // Check that the Object.prototype hasn't been altered WRT empty elements.
    elements = initial_object_proto->elements();
    if (elements != roots.empty_fixed_array() &&
        elements != roots.empty_slow_element_dictionary()) {
      DCHECK_EQ(false, cell_reports_intact);
      return cell_reports_intact;
    }
  
    // Check that the Array.prototype has the Object.prototype as its
    // [[Prototype]] and that the Object.prototype has a null [[Prototype]].
    PrototypeIterator iter(this, initial_array_proto);
    if (iter.IsAtEnd() || iter.GetCurrent() != initial_object_proto) {
      DCHECK_EQ(false, cell_reports_intact);
      DCHECK(!has_pending_exception());
      return cell_reports_intact;
    }
    iter.Advance();
    if (!iter.IsAtEnd()) {
      DCHECK_EQ(false, cell_reports_intact);
      DCHECK(!has_pending_exception());
      return cell_reports_intact;
    }
    DCHECK(!has_pending_exception());
  
    // Check that the String.prototype hasn't been altered WRT empty elements.
    elements = initial_string_proto->elements();
    if (elements != roots.empty_fixed_array() &&
        elements != roots.empty_slow_element_dictionary()) {
      DCHECK_EQ(false, cell_reports_intact);
      return cell_reports_intact;
    }
  
    // Check that the String.prototype has the Object.prototype
    // as its [[Prototype]] still.
    if (initial_string_proto->map()->prototype() != initial_object_proto) {
      DCHECK_EQ(false, cell_reports_intact);
      return cell_reports_intact;
    }
  #endif
  
    return cell_reports_intact;
  }
  
  bool Isolate::IsNoElementsProtectorIntact() {
    return Isolate::IsNoElementsProtectorIntact(context());
  }
  
  bool Isolate::IsIsConcatSpreadableLookupChainIntact() {
    Cell is_concat_spreadable_cell = heap()->is_concat_spreadable_protector();
    bool is_is_concat_spreadable_set =
        Smi::ToInt(is_concat_spreadable_cell->value()) == kProtectorInvalid;
  #ifdef DEBUG
    Map root_array_map =
        raw_native_context()->GetInitialJSArrayMap(GetInitialFastElementsKind());
    if (root_array_map.is_null()) {
      // Ignore the value of is_concat_spreadable during bootstrap.
      return !is_is_concat_spreadable_set;
    }
    Handle<Object> array_prototype(array_function()->prototype(), this);
    Handle<Symbol> key = factory()->is_concat_spreadable_symbol();
    Handle<Object> value;
    LookupIterator it(this, array_prototype, key);
    if (it.IsFound() && !JSReceiver::GetDataProperty(&it)->IsUndefined(this)) {
      // TODO(cbruni): Currently we do not revert if we unset the
      // @@isConcatSpreadable property on Array.prototype or Object.prototype
      // hence the reverse implication doesn't hold.
      DCHECK(is_is_concat_spreadable_set);
      return false;
    }
  #endif  // DEBUG
  
    return !is_is_concat_spreadable_set;
  }
  
  bool Isolate::IsIsConcatSpreadableLookupChainIntact(JSReceiver receiver) {
    if (!IsIsConcatSpreadableLookupChainIntact()) return false;
    return !receiver->HasProxyInPrototype(this);
  }
  
  bool Isolate::IsPromiseHookProtectorIntact() {
    PropertyCell promise_hook_cell = heap()->promise_hook_protector();
    bool is_promise_hook_protector_intact =
        Smi::ToInt(promise_hook_cell->value()) == kProtectorValid;
    DCHECK_IMPLIES(is_promise_hook_protector_intact,
                   !promise_hook_or_async_event_delegate_);
    DCHECK_IMPLIES(is_promise_hook_protector_intact,
                   !promise_hook_or_debug_is_active_or_async_event_delegate_);
    return is_promise_hook_protector_intact;
  }
  
  bool Isolate::IsPromiseResolveLookupChainIntact() {
    Cell promise_resolve_cell = heap()->promise_resolve_protector();
    bool is_promise_resolve_protector_intact =
        Smi::ToInt(promise_resolve_cell->value()) == kProtectorValid;
    return is_promise_resolve_protector_intact;
  }
  
  bool Isolate::IsPromiseThenLookupChainIntact() {
    PropertyCell promise_then_cell = heap()->promise_then_protector();
    bool is_promise_then_protector_intact =
        Smi::ToInt(promise_then_cell->value()) == kProtectorValid;
    return is_promise_then_protector_intact;
  }
  
  bool Isolate::IsPromiseThenLookupChainIntact(Handle<JSReceiver> receiver) {
    DisallowHeapAllocation no_gc;
    if (!receiver->IsJSPromise()) return false;
    if (!IsInAnyContext(receiver->map()->prototype(),
                        Context::PROMISE_PROTOTYPE_INDEX)) {
      return false;
    }
    return IsPromiseThenLookupChainIntact();
  }
  
  void Isolate::UpdateNoElementsProtectorOnSetElement(Handle<JSObject> object) {
    DisallowHeapAllocation no_gc;
    if (!object->map()->is_prototype_map()) return;
    if (!IsNoElementsProtectorIntact()) return;
    if (!IsArrayOrObjectOrStringPrototype(*object)) return;
    PropertyCell::SetValueWithInvalidation(
        this, factory()->no_elements_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
  }
  
  void Isolate::InvalidateIsConcatSpreadableProtector() {
    DCHECK(factory()->is_concat_spreadable_protector()->value()->IsSmi());
    DCHECK(IsIsConcatSpreadableLookupChainIntact());
    factory()->is_concat_spreadable_protector()->set_value(
        Smi::FromInt(kProtectorInvalid));
    DCHECK(!IsIsConcatSpreadableLookupChainIntact());
  }
  
  void Isolate::InvalidateArrayConstructorProtector() {
    DCHECK(factory()->array_constructor_protector()->value()->IsSmi());
    DCHECK(IsArrayConstructorIntact());
    factory()->array_constructor_protector()->set_value(
        Smi::FromInt(kProtectorInvalid));
    DCHECK(!IsArrayConstructorIntact());
  }
  
  void Isolate::InvalidateArraySpeciesProtector() {
    DCHECK(factory()->array_species_protector()->value()->IsSmi());
    DCHECK(IsArraySpeciesLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->array_species_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsArraySpeciesLookupChainIntact());
  }
  
  void Isolate::InvalidateTypedArraySpeciesProtector() {
    DCHECK(factory()->typed_array_species_protector()->value()->IsSmi());
    DCHECK(IsTypedArraySpeciesLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->typed_array_species_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsTypedArraySpeciesLookupChainIntact());
  }
  
  void Isolate::InvalidateRegExpSpeciesProtector() {
    DCHECK(factory()->regexp_species_protector()->value()->IsSmi());
    DCHECK(IsRegExpSpeciesLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->regexp_species_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsRegExpSpeciesLookupChainIntact());
  }
  
  void Isolate::InvalidatePromiseSpeciesProtector() {
    DCHECK(factory()->promise_species_protector()->value()->IsSmi());
    DCHECK(IsPromiseSpeciesLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->promise_species_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsPromiseSpeciesLookupChainIntact());
  }
  
  void Isolate::InvalidateStringLengthOverflowProtector() {
    DCHECK(factory()->string_length_protector()->value()->IsSmi());
    DCHECK(IsStringLengthOverflowIntact());
    factory()->string_length_protector()->set_value(
        Smi::FromInt(kProtectorInvalid));
    DCHECK(!IsStringLengthOverflowIntact());
  }
  
  void Isolate::InvalidateArrayIteratorProtector() {
    DCHECK(factory()->array_iterator_protector()->value()->IsSmi());
    DCHECK(IsArrayIteratorLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->array_iterator_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsArrayIteratorLookupChainIntact());
  }
  
  void Isolate::InvalidateMapIteratorProtector() {
    DCHECK(factory()->map_iterator_protector()->value()->IsSmi());
    DCHECK(IsMapIteratorLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->map_iterator_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsMapIteratorLookupChainIntact());
  }
  
  void Isolate::InvalidateSetIteratorProtector() {
    DCHECK(factory()->set_iterator_protector()->value()->IsSmi());
    DCHECK(IsSetIteratorLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->set_iterator_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsSetIteratorLookupChainIntact());
  }
  
  void Isolate::InvalidateStringIteratorProtector() {
    DCHECK(factory()->string_iterator_protector()->value()->IsSmi());
    DCHECK(IsStringIteratorLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->string_iterator_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsStringIteratorLookupChainIntact());
  }
  
  void Isolate::InvalidateArrayBufferDetachingProtector() {
    DCHECK(factory()->array_buffer_detaching_protector()->value()->IsSmi());
    DCHECK(IsArrayBufferDetachingIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->array_buffer_detaching_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsArrayBufferDetachingIntact());
  }
  
  void Isolate::InvalidatePromiseHookProtector() {
    DCHECK(factory()->promise_hook_protector()->value()->IsSmi());
    DCHECK(IsPromiseHookProtectorIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->promise_hook_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsPromiseHookProtectorIntact());
  }
  
  void Isolate::InvalidatePromiseResolveProtector() {
    DCHECK(factory()->promise_resolve_protector()->value()->IsSmi());
    DCHECK(IsPromiseResolveLookupChainIntact());
    factory()->promise_resolve_protector()->set_value(
        Smi::FromInt(kProtectorInvalid));
    DCHECK(!IsPromiseResolveLookupChainIntact());
  }
  
  void Isolate::InvalidatePromiseThenProtector() {
    DCHECK(factory()->promise_then_protector()->value()->IsSmi());
    DCHECK(IsPromiseThenLookupChainIntact());
    PropertyCell::SetValueWithInvalidation(
        this, factory()->promise_then_protector(),
        handle(Smi::FromInt(kProtectorInvalid), this));
    DCHECK(!IsPromiseThenLookupChainIntact());
  }
  
  bool Isolate::IsAnyInitialArrayPrototype(Handle<JSArray> array) {
    DisallowHeapAllocation no_gc;
    return IsInAnyContext(*array, Context::INITIAL_ARRAY_PROTOTYPE_INDEX);
  }
  
  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));
    int entry = dictionary->FindEntry(this, key);
    Handle<Symbol> symbol;
    if (entry == NameDictionary::kNotFound) {
      symbol =
          private_symbol ? factory()->NewPrivateSymbol() : factory()->NewSymbol();
      symbol->set_name(*key);
      dictionary = NameDictionary::Add(this, dictionary, key, symbol,
                                       PropertyDetails::Empty(), &entry);
      switch (dictionary_index) {
        case RootIndex::kPublicSymbolTable:
          symbol->set_is_public(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() {
    if (!handle_scope_implementer()->CallDepthIsZero()) return;
  
    bool run_microtasks =
        default_microtask_queue()->size() &&
        !default_microtask_queue()->HasMicrotasksSuppressions() &&
        handle_scope_implementer()->microtasks_policy() ==
            v8::MicrotasksPolicy::kAuto;
  
    if (run_microtasks) {
      RunMicrotasks();
    } else {
      // TODO(marja): (spec) The discussion about when to clear the KeepDuringJob
      // set is still open (whether to clear it after every microtask or once
      // during a microtask checkpoint). See also
      // https://github.com/tc39/proposal-weakrefs/issues/39 .
      heap()->ClearKeepDuringJobSet();
    }
  
    if (call_completed_callbacks_.empty()) return;
    // Fire callbacks.  Increase call depth to prevent recursive callbacks.
    v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(this);
    v8::Isolate::SuppressMicrotaskExecutionScope suppress(isolate);
    std::vector<CallCompletedCallback> callbacks(call_completed_callbacks_);
    for (auto& callback : callbacks) {
      callback(reinterpret_cast<v8::Isolate*>(this));
    }
  }
  
  void Isolate::PromiseHookStateUpdated() {
    bool promise_hook_or_async_event_delegate =
        promise_hook_ || async_event_delegate_;
    bool promise_hook_or_debug_is_active_or_async_event_delegate =
        promise_hook_or_async_event_delegate || debug()->is_active();
    if (promise_hook_or_debug_is_active_or_async_event_delegate &&
        IsPromiseHookProtectorIntact()) {
      HandleScope scope(this);
      InvalidatePromiseHookProtector();
    }
    promise_hook_or_async_event_delegate_ = promise_hook_or_async_event_delegate;
    promise_hook_or_debug_is_active_or_async_event_delegate_ =
        promise_hook_or_debug_is_active_or_async_event_delegate;
  }
  
  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) {
    v8::Local<v8::Context> api_context =
        v8::Utils::ToLocal(Handle<Context>(native_context()));
  
    if (host_import_module_dynamically_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;
    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);
  }
  
  void Isolate::SetHostImportModuleDynamicallyCallback(
      HostImportModuleDynamicallyCallback callback) {
    host_import_module_dynamically_callback_ = callback;
  }
  
  Handle<JSObject> Isolate::RunHostInitializeImportMetaObjectCallback(
      Handle<Module> module) {
    Handle<Object> host_meta(module->import_meta(), this);
    if (host_meta->IsTheHole(this)) {
      host_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(module),
            v8::Local<v8::Object>::Cast(v8::Utils::ToLocal(host_meta)));
      }
      module->set_import_meta(*host_meta);
    }
    return Handle<JSObject>::cast(host_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);
  }
  
  void Isolate::SetPrepareStackTraceCallback(PrepareStackTraceCallback callback) {
    prepare_stack_trace_callback_ = callback;
  }
  
  bool Isolate::HasPrepareStackTraceCallback() const {
    return prepare_stack_trace_callback_ != nullptr;
  }
  
  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::RunPromiseHook(PromiseHookType type, Handle<JSPromise> promise,
                               Handle<Object> parent) {
    RunPromiseHookForAsyncEventDelegate(type, promise);
    if (promise_hook_ == nullptr) return;
    promise_hook_(type, v8::Utils::PromiseToLocal(promise),
                  v8::Utils::ToLocal(parent));
  }
  
  void Isolate::RunPromiseHookForAsyncEventDelegate(PromiseHookType type,
                                                    Handle<JSPromise> promise) {
    if (!async_event_delegate_) return;
    if (type == PromiseHookType::kResolve) return;
  
    if (type == PromiseHookType::kBefore) {
      if (!promise->async_task_id()) return;
      async_event_delegate_->AsyncEventOccurred(debug::kDebugWillHandle,
                                                promise->async_task_id(), false);
    } else if (type == PromiseHookType::kAfter) {
      if (!promise->async_task_id()) return;
      async_event_delegate_->AsyncEventOccurred(debug::kDebugDidHandle,
                                                promise->async_task_id(), false);
    } else {
      DCHECK(type == 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;
    Handle<FixedArray> stack_trace;
    if (event != v8::kPromiseHandlerAddedAfterReject && value->IsJSObject()) {
      stack_trace = GetDetailedStackTrace(Handle<JSObject>::cast(value));
    }
    promise_reject_callback_(v8::PromiseRejectMessage(
        v8::Utils::PromiseToLocal(promise), event, v8::Utils::ToLocal(value),
        v8::Utils::StackTraceToLocal(stack_trace)));
  }
  
  void Isolate::RunMicrotasks() {
    // Increase call depth to prevent recursive callbacks.
    v8::Isolate::SuppressMicrotaskExecutionScope suppress(
        reinterpret_cast<v8::Isolate*>(this));
    MicrotaskQueue* microtask_queue = default_microtask_queue();
    if (microtask_queue->size()) {
      TRACE_EVENT0("v8.execute", "RunMicrotasks");
      TRACE_EVENT_CALL_STATS_SCOPED(this, "v8", "V8.RunMicrotasks");
  
      HandleScopeImplementer::EnteredContextRewindScope scope(
          handle_scope_implementer());
      // If execution is terminating, bail out, clean up, and propagate to
      // TryCatch scope.
      if (microtask_queue->RunMicrotasks(this) < 0) {
        SetTerminationOnExternalTryCatch();
      }
      DCHECK_EQ(0, microtask_queue->size());
    }
    // TODO(marja): (spec) The discussion about when to clear the KeepDuringJob
    // set is still open (whether to clear it after every microtask or once
    // during a microtask checkpoint). See also
    // https://github.com/tc39/proposal-weakrefs/issues/39 .
    heap()->ClearKeepDuringJobSet();
  
    microtask_queue->FireMicrotasksCompletedCallback(this);
  }
  
  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.
    if (heap_.gc_state() == Heap::NOT_IN_GC) {
      if (use_counter_callback_) {
        HandleScope handle_scope(this);
        use_counter_callback_(reinterpret_cast<v8::Isolate*>(this), feature);
      }
    } else {
      heap_.IncrementDeferredCount(feature);
    }
  }
  
  // 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::kZero, this));
    detached_contexts = WeakArrayList::AddToEnd(this, detached_contexts,
                                                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::SetRAILMode(RAILMode rail_mode) {
    RAILMode old_rail_mode = rail_mode_.Value();
    if (old_rail_mode != PERFORMANCE_LOAD && rail_mode == PERFORMANCE_LOAD) {
      base::MutexGuard guard(&rail_mutex_);
      load_start_time_ms_ = heap()->MonotonicallyIncreasingTimeInMs();
    }
    rail_mode_.SetValue(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) {
    if (!is_profiling()) return;
    StateTag state = current_vm_state();
    DCHECK(state == EXTERNAL || state == IDLE);
    if (js_entry_sp() != kNullAddress) return;
    if (is_idle) {
      set_current_vm_state(IDLE);
    } else if (state == IDLE) {
      set_current_vm_state(EXTERNAL);
    }
  }
  
  #ifdef V8_INTL_SUPPORT
  icu::UObject* Isolate::get_cached_icu_object(ICUObjectCacheType cache_type) {
    return icu_object_cache_[cache_type].get();
  }
  
  void Isolate::set_icu_object_in_cache(ICUObjectCacheType cache_type,
                                        std::shared_ptr<icu::UObject> obj) {
    icu_object_cache_[cache_type] = obj;
  }
  
  void Isolate::clear_cached_icu_object(ICUObjectCacheType cache_type) {
    icu_object_cache_.erase(cache_type);
  }
  #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), prev_(isolate->save_context()) {
    if (!isolate->context().is_null()) {
      context_ = Handle<Context>(isolate->context(), isolate);
    }
    isolate->set_save_context(this);
  
    c_entry_fp_ = isolate->c_entry_fp(isolate->thread_local_top());
  }
  
  SaveContext::~SaveContext() {
    isolate_->set_context(context_.is_null() ? Context() : *context_);
    isolate_->set_save_context(prev_);
  }
  
  bool SaveContext::IsBelowFrame(StandardFrame* frame) {
    return (c_entry_fp_ == 0) || (c_entry_fp_ > frame->sp());
  }
  
  #ifdef DEBUG
  AssertNoContextChange::AssertNoContextChange(Isolate* isolate)
      : isolate_(isolate), context_(isolate->context(), isolate) {}
  #endif  // DEBUG
  
  bool InterruptsScope::Intercept(StackGuard::InterruptFlag flag) {
    InterruptsScope* last_postpone_scope = nullptr;
    for (InterruptsScope* current = this; current; current = current->prev_) {
      // We only consider scopes related to passed flag.
      if (!(current->intercept_mask_ & flag)) continue;
      if (current->mode_ == kRunInterrupts) {
        // If innermost scope is kRunInterrupts scope, prevent interrupt from
        // being intercepted.
        break;
      } else {
        DCHECK_EQ(current->mode_, kPostponeInterrupts);
        last_postpone_scope = current;
      }
    }
    // If there is no postpone scope for passed flag then we should not intercept.
    if (!last_postpone_scope) return false;
    last_postpone_scope->intercepted_flags_ |= flag;
    return true;
  }
  
  #undef TRACE_ISOLATE
  
  }  // namespace internal
  }  // namespace v8
  