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.
  
  #ifndef V8_API_H_
  #define V8_API_H_
  
  #include "include/v8-testing.h"
  #include "src/contexts.h"
  #include "src/debug/debug-interface.h"
  #include "src/detachable-vector.h"
  #include "src/factory.h"
  #include "src/isolate.h"
  
  namespace v8 {
  
  // Constants used in the implementation of the API.  The most natural thing
  // would usually be to place these with the classes that use them, but
  // we want to keep them out of v8.h because it is an externally
  // visible file.
  class Consts {
   public:
    enum TemplateType {
      FUNCTION_TEMPLATE = 0,
      OBJECT_TEMPLATE = 1
    };
  };
  
  template <typename T> inline T ToCData(v8::internal::Object* obj) {
    STATIC_ASSERT(sizeof(T) == sizeof(v8::internal::Address));
    if (obj == v8::internal::Smi::kZero) return nullptr;
    return reinterpret_cast<T>(
        reinterpret_cast<intptr_t>(
            v8::internal::Foreign::cast(obj)->foreign_address()));
  }
  
  
  template <typename T>
  inline v8::internal::Handle<v8::internal::Object> FromCData(
      v8::internal::Isolate* isolate, T obj) {
    STATIC_ASSERT(sizeof(T) == sizeof(v8::internal::Address));
    if (obj == nullptr) return handle(v8::internal::Smi::kZero, isolate);
    return isolate->factory()->NewForeign(
        reinterpret_cast<v8::internal::Address>(reinterpret_cast<intptr_t>(obj)));
  }
  
  
  class ApiFunction {
   public:
    explicit ApiFunction(v8::internal::Address addr) : addr_(addr) { }
    v8::internal::Address address() { return addr_; }
   private:
    v8::internal::Address addr_;
  };
  
  
  
  class RegisteredExtension {
   public:
    explicit RegisteredExtension(Extension* extension);
    static void Register(RegisteredExtension* that);
    static void UnregisterAll();
    Extension* extension() { return extension_; }
    RegisteredExtension* next() { return next_; }
    static RegisteredExtension* first_extension() { return first_extension_; }
   private:
    Extension* extension_;
    RegisteredExtension* next_;
    static RegisteredExtension* first_extension_;
  };
  
  #define OPEN_HANDLE_LIST(V)                    \
    V(Template, TemplateInfo)                    \
    V(FunctionTemplate, FunctionTemplateInfo)    \
    V(ObjectTemplate, ObjectTemplateInfo)        \
    V(Signature, FunctionTemplateInfo)           \
    V(AccessorSignature, FunctionTemplateInfo)   \
    V(Data, Object)                              \
    V(RegExp, JSRegExp)                          \
    V(Object, JSReceiver)                        \
    V(Array, JSArray)                            \
    V(Map, JSMap)                                \
    V(Set, JSSet)                                \
    V(ArrayBuffer, JSArrayBuffer)                \
    V(ArrayBufferView, JSArrayBufferView)        \
    V(TypedArray, JSTypedArray)                  \
    V(Uint8Array, JSTypedArray)                  \
    V(Uint8ClampedArray, JSTypedArray)           \
    V(Int8Array, JSTypedArray)                   \
    V(Uint16Array, JSTypedArray)                 \
    V(Int16Array, JSTypedArray)                  \
    V(Uint32Array, JSTypedArray)                 \
    V(Int32Array, JSTypedArray)                  \
    V(Float32Array, JSTypedArray)                \
    V(Float64Array, JSTypedArray)                \
    V(DataView, JSDataView)                      \
    V(SharedArrayBuffer, JSArrayBuffer)          \
    V(Name, Name)                                \
    V(String, String)                            \
    V(Symbol, Symbol)                            \
    V(Script, JSFunction)                        \
    V(UnboundScript, SharedFunctionInfo)         \
    V(Module, Module)                            \
    V(Function, JSReceiver)                      \
    V(Message, JSMessageObject)                  \
    V(Context, Context)                          \
    V(External, Object)                          \
    V(StackTrace, FixedArray)                    \
    V(StackFrame, StackFrameInfo)                \
    V(Proxy, JSProxy)                            \
    V(NativeWeakMap, JSWeakMap)                  \
    V(debug::GeneratorObject, JSGeneratorObject) \
    V(debug::Script, Script)                     \
    V(Promise, JSPromise)                        \
    V(Primitive, Object)                         \
    V(PrimitiveArray, FixedArray)                \
    V(ScriptOrModule, Script)
  
  class Utils {
   public:
    static inline bool ApiCheck(bool condition,
                                const char* location,
                                const char* message) {
      if (!condition) Utils::ReportApiFailure(location, message);
      return condition;
    }
    static void ReportOOMFailure(const char* location, bool is_heap_oom);
  
    static inline Local<Context> ToLocal(
        v8::internal::Handle<v8::internal::Context> obj);
    static inline Local<Value> ToLocal(
        v8::internal::Handle<v8::internal::Object> obj);
    static inline Local<Module> ToLocal(
        v8::internal::Handle<v8::internal::Module> obj);
    static inline Local<Name> ToLocal(
        v8::internal::Handle<v8::internal::Name> obj);
    static inline Local<String> ToLocal(
        v8::internal::Handle<v8::internal::String> obj);
    static inline Local<Symbol> ToLocal(
        v8::internal::Handle<v8::internal::Symbol> obj);
    static inline Local<RegExp> ToLocal(
        v8::internal::Handle<v8::internal::JSRegExp> obj);
    static inline Local<Object> ToLocal(
        v8::internal::Handle<v8::internal::JSReceiver> obj);
    static inline Local<Object> ToLocal(
        v8::internal::Handle<v8::internal::JSObject> obj);
    static inline Local<Function> ToLocal(
        v8::internal::Handle<v8::internal::JSFunction> obj);
    static inline Local<Array> ToLocal(
        v8::internal::Handle<v8::internal::JSArray> obj);
    static inline Local<Map> ToLocal(
        v8::internal::Handle<v8::internal::JSMap> obj);
    static inline Local<Set> ToLocal(
        v8::internal::Handle<v8::internal::JSSet> obj);
    static inline Local<Proxy> ToLocal(
        v8::internal::Handle<v8::internal::JSProxy> obj);
    static inline Local<ArrayBuffer> ToLocal(
        v8::internal::Handle<v8::internal::JSArrayBuffer> obj);
    static inline Local<ArrayBufferView> ToLocal(
        v8::internal::Handle<v8::internal::JSArrayBufferView> obj);
    static inline Local<DataView> ToLocal(
        v8::internal::Handle<v8::internal::JSDataView> obj);
    static inline Local<TypedArray> ToLocal(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Uint8Array> ToLocalUint8Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Uint8ClampedArray> ToLocalUint8ClampedArray(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Int8Array> ToLocalInt8Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Uint16Array> ToLocalUint16Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Int16Array> ToLocalInt16Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Uint32Array> ToLocalUint32Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Int32Array> ToLocalInt32Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Float32Array> ToLocalFloat32Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
    static inline Local<Float64Array> ToLocalFloat64Array(
        v8::internal::Handle<v8::internal::JSTypedArray> obj);
  
    static inline Local<SharedArrayBuffer> ToLocalShared(
        v8::internal::Handle<v8::internal::JSArrayBuffer> obj);
  
    static inline Local<Message> MessageToLocal(
        v8::internal::Handle<v8::internal::Object> obj);
    static inline Local<Promise> PromiseToLocal(
        v8::internal::Handle<v8::internal::JSObject> obj);
    static inline Local<StackTrace> StackTraceToLocal(
        v8::internal::Handle<v8::internal::FixedArray> obj);
    static inline Local<StackFrame> StackFrameToLocal(
        v8::internal::Handle<v8::internal::StackFrameInfo> obj);
    static inline Local<Number> NumberToLocal(
        v8::internal::Handle<v8::internal::Object> obj);
    static inline Local<Integer> IntegerToLocal(
        v8::internal::Handle<v8::internal::Object> obj);
    static inline Local<Uint32> Uint32ToLocal(
        v8::internal::Handle<v8::internal::Object> obj);
    static inline Local<FunctionTemplate> ToLocal(
        v8::internal::Handle<v8::internal::FunctionTemplateInfo> obj);
    static inline Local<ObjectTemplate> ToLocal(
        v8::internal::Handle<v8::internal::ObjectTemplateInfo> obj);
    static inline Local<Signature> SignatureToLocal(
        v8::internal::Handle<v8::internal::FunctionTemplateInfo> obj);
    static inline Local<AccessorSignature> AccessorSignatureToLocal(
        v8::internal::Handle<v8::internal::FunctionTemplateInfo> obj);
    static inline Local<External> ExternalToLocal(
        v8::internal::Handle<v8::internal::JSObject> obj);
    static inline Local<NativeWeakMap> NativeWeakMapToLocal(
        v8::internal::Handle<v8::internal::JSWeakMap> obj);
    static inline Local<Function> CallableToLocal(
        v8::internal::Handle<v8::internal::JSReceiver> obj);
    static inline Local<Primitive> ToLocalPrimitive(
        v8::internal::Handle<v8::internal::Object> obj);
    static inline Local<PrimitiveArray> ToLocal(
        v8::internal::Handle<v8::internal::FixedArray> obj);
    static inline Local<ScriptOrModule> ScriptOrModuleToLocal(
        v8::internal::Handle<v8::internal::Script> obj);
  
  #define DECLARE_OPEN_HANDLE(From, To) \
    static inline v8::internal::Handle<v8::internal::To> \
        OpenHandle(const From* that, bool allow_empty_handle = false);
  
  OPEN_HANDLE_LIST(DECLARE_OPEN_HANDLE)
  
  #undef DECLARE_OPEN_HANDLE
  
    template<class From, class To>
    static inline Local<To> Convert(v8::internal::Handle<From> obj) {
      DCHECK(obj.is_null() ||
             (obj->IsSmi() ||
              !obj->IsTheHole(i::HeapObject::cast(*obj)->GetIsolate())));
      return Local<To>(reinterpret_cast<To*>(obj.location()));
    }
  
    template <class T>
    static inline v8::internal::Handle<v8::internal::Object> OpenPersistent(
        const v8::Persistent<T>& persistent) {
      return v8::internal::Handle<v8::internal::Object>(
          reinterpret_cast<v8::internal::Object**>(persistent.val_));
    }
  
    template <class T>
    static inline v8::internal::Handle<v8::internal::Object> OpenPersistent(
        v8::Persistent<T>* persistent) {
      return OpenPersistent(*persistent);
    }
  
    template <class From, class To>
    static inline v8::internal::Handle<To> OpenHandle(v8::Local<From> handle) {
      return OpenHandle(*handle);
    }
  
   private:
    static void ReportApiFailure(const char* location, const char* message);
  };
  
  
  template <class T>
  inline T* ToApi(v8::internal::Handle<v8::internal::Object> obj) {
    return reinterpret_cast<T*>(obj.location());
  }
  
  template <class T>
  inline v8::Local<T> ToApiHandle(
      v8::internal::Handle<v8::internal::Object> obj) {
    return Utils::Convert<v8::internal::Object, T>(obj);
  }
  
  
  template <class T>
  inline bool ToLocal(v8::internal::MaybeHandle<v8::internal::Object> maybe,
                      Local<T>* local) {
    v8::internal::Handle<v8::internal::Object> handle;
    if (maybe.ToHandle(&handle)) {
      *local = Utils::Convert<v8::internal::Object, T>(handle);
      return true;
    }
    return false;
  }
  
  
  // Implementations of ToLocal
  
  #define MAKE_TO_LOCAL(Name, From, To)                                       \
    Local<v8::To> Utils::Name(v8::internal::Handle<v8::internal::From> obj) { \
      return Convert<v8::internal::From, v8::To>(obj);  \
    }
  
  
  #define MAKE_TO_LOCAL_TYPED_ARRAY(Type, typeName, TYPE, ctype, size)  \
    Local<v8::Type##Array> Utils::ToLocal##Type##Array(                 \
        v8::internal::Handle<v8::internal::JSTypedArray> obj) {         \
      DCHECK(obj->type() == v8::internal::kExternal##Type##Array);      \
      return Convert<v8::internal::JSTypedArray, v8::Type##Array>(obj); \
    }
  
  
  MAKE_TO_LOCAL(ToLocal, Context, Context)
  MAKE_TO_LOCAL(ToLocal, Object, Value)
  MAKE_TO_LOCAL(ToLocal, Module, Module)
  MAKE_TO_LOCAL(ToLocal, Name, Name)
  MAKE_TO_LOCAL(ToLocal, String, String)
  MAKE_TO_LOCAL(ToLocal, Symbol, Symbol)
  MAKE_TO_LOCAL(ToLocal, JSRegExp, RegExp)
  MAKE_TO_LOCAL(ToLocal, JSReceiver, Object)
  MAKE_TO_LOCAL(ToLocal, JSObject, Object)
  MAKE_TO_LOCAL(ToLocal, JSFunction, Function)
  MAKE_TO_LOCAL(ToLocal, JSArray, Array)
  MAKE_TO_LOCAL(ToLocal, JSMap, Map)
  MAKE_TO_LOCAL(ToLocal, JSSet, Set)
  MAKE_TO_LOCAL(ToLocal, JSProxy, Proxy)
  MAKE_TO_LOCAL(ToLocal, JSArrayBuffer, ArrayBuffer)
  MAKE_TO_LOCAL(ToLocal, JSArrayBufferView, ArrayBufferView)
  MAKE_TO_LOCAL(ToLocal, JSDataView, DataView)
  MAKE_TO_LOCAL(ToLocal, JSTypedArray, TypedArray)
  MAKE_TO_LOCAL(ToLocalShared, JSArrayBuffer, SharedArrayBuffer)
  
  TYPED_ARRAYS(MAKE_TO_LOCAL_TYPED_ARRAY)
  
  MAKE_TO_LOCAL(ToLocal, FunctionTemplateInfo, FunctionTemplate)
  MAKE_TO_LOCAL(ToLocal, ObjectTemplateInfo, ObjectTemplate)
  MAKE_TO_LOCAL(SignatureToLocal, FunctionTemplateInfo, Signature)
  MAKE_TO_LOCAL(AccessorSignatureToLocal, FunctionTemplateInfo, AccessorSignature)
  MAKE_TO_LOCAL(MessageToLocal, Object, Message)
  MAKE_TO_LOCAL(PromiseToLocal, JSObject, Promise)
  MAKE_TO_LOCAL(StackTraceToLocal, FixedArray, StackTrace)
  MAKE_TO_LOCAL(StackFrameToLocal, StackFrameInfo, StackFrame)
  MAKE_TO_LOCAL(NumberToLocal, Object, Number)
  MAKE_TO_LOCAL(IntegerToLocal, Object, Integer)
  MAKE_TO_LOCAL(Uint32ToLocal, Object, Uint32)
  MAKE_TO_LOCAL(ExternalToLocal, JSObject, External)
  MAKE_TO_LOCAL(NativeWeakMapToLocal, JSWeakMap, NativeWeakMap)
  MAKE_TO_LOCAL(CallableToLocal, JSReceiver, Function)
  MAKE_TO_LOCAL(ToLocalPrimitive, Object, Primitive)
  MAKE_TO_LOCAL(ToLocal, FixedArray, PrimitiveArray)
  MAKE_TO_LOCAL(ScriptOrModuleToLocal, Script, ScriptOrModule)
  
  #undef MAKE_TO_LOCAL_TYPED_ARRAY
  #undef MAKE_TO_LOCAL
  
  
  // Implementations of OpenHandle
  
  #define MAKE_OPEN_HANDLE(From, To)                                             \
    v8::internal::Handle<v8::internal::To> Utils::OpenHandle(                    \
        const v8::From* that, bool allow_empty_handle) {                         \
      DCHECK(allow_empty_handle || that != nullptr);                             \
      DCHECK(that == nullptr ||                                                  \
             (*reinterpret_cast<v8::internal::Object* const*>(that))->Is##To()); \
      return v8::internal::Handle<v8::internal::To>(                             \
          reinterpret_cast<v8::internal::To**>(const_cast<v8::From*>(that)));    \
    }
  
  OPEN_HANDLE_LIST(MAKE_OPEN_HANDLE)
  
  #undef MAKE_OPEN_HANDLE
  #undef OPEN_HANDLE_LIST
  
  extern Isolate* IsolateNewImpl(internal::Isolate* isolate,
                                 const Isolate::CreateParams& params);
  
  namespace internal {
  
  class V8_EXPORT_PRIVATE DeferredHandles {
   public:
    ~DeferredHandles();
  
   private:
    DeferredHandles(Object** first_block_limit, Isolate* isolate)
        : next_(nullptr),
          previous_(nullptr),
          first_block_limit_(first_block_limit),
          isolate_(isolate) {
      isolate->LinkDeferredHandles(this);
    }
  
    void Iterate(RootVisitor* v);
  
    std::vector<Object**> blocks_;
    DeferredHandles* next_;
    DeferredHandles* previous_;
    Object** first_block_limit_;
    Isolate* isolate_;
  
    friend class HandleScopeImplementer;
    friend class Isolate;
  };
  
  
  // This class is here in order to be able to declare it a friend of
  // HandleScope.  Moving these methods to be members of HandleScope would be
  // neat in some ways, but it would expose internal implementation details in
  // our public header file, which is undesirable.
  //
  // An isolate has a single instance of this class to hold the current thread's
  // data. In multithreaded V8 programs this data is copied in and out of storage
  // so that the currently executing thread always has its own copy of this
  // data.
  class HandleScopeImplementer {
   public:
    explicit HandleScopeImplementer(Isolate* isolate)
        : isolate_(isolate),
          microtask_context_(nullptr),
          spare_(nullptr),
          call_depth_(0),
          microtasks_depth_(0),
          microtasks_suppressions_(0),
          entered_context_count_during_microtasks_(0),
  #ifdef DEBUG
          debug_microtasks_depth_(0),
  #endif
          microtasks_policy_(v8::MicrotasksPolicy::kAuto),
          last_handle_before_deferred_block_(nullptr) {
    }
  
    ~HandleScopeImplementer() {
      DeleteArray(spare_);
    }
  
    // Threading support for handle data.
    static int ArchiveSpacePerThread();
    char* RestoreThread(char* from);
    char* ArchiveThread(char* to);
    void FreeThreadResources();
  
    // Garbage collection support.
    void Iterate(v8::internal::RootVisitor* v);
    static char* Iterate(v8::internal::RootVisitor* v, char* data);
  
    inline internal::Object** GetSpareOrNewBlock();
    inline void DeleteExtensions(internal::Object** prev_limit);
  
    // Call depth represents nested v8 api calls.
    inline void IncrementCallDepth() {call_depth_++;}
    inline void DecrementCallDepth() {call_depth_--;}
    inline bool CallDepthIsZero() { return call_depth_ == 0; }
  
    // Microtasks scope depth represents nested scopes controlling microtasks
    // invocation, which happens when depth reaches zero.
    inline void IncrementMicrotasksScopeDepth() {microtasks_depth_++;}
    inline void DecrementMicrotasksScopeDepth() {microtasks_depth_--;}
    inline int GetMicrotasksScopeDepth() { return microtasks_depth_; }
  
    // Possibly nested microtasks suppression scopes prevent microtasks
    // from running.
    inline void IncrementMicrotasksSuppressions() {microtasks_suppressions_++;}
    inline void DecrementMicrotasksSuppressions() {microtasks_suppressions_--;}
    inline bool HasMicrotasksSuppressions() { return !!microtasks_suppressions_; }
  
  #ifdef DEBUG
    // In debug we check that calls not intended to invoke microtasks are
    // still correctly wrapped with microtask scopes.
    inline void IncrementDebugMicrotasksScopeDepth() {debug_microtasks_depth_++;}
    inline void DecrementDebugMicrotasksScopeDepth() {debug_microtasks_depth_--;}
    inline bool DebugMicrotasksScopeDepthIsZero() {
      return debug_microtasks_depth_ == 0;
    }
  #endif
  
    inline void set_microtasks_policy(v8::MicrotasksPolicy policy);
    inline v8::MicrotasksPolicy microtasks_policy() const;
  
    inline void EnterContext(Handle<Context> context);
    inline void LeaveContext();
    inline bool LastEnteredContextWas(Handle<Context> context);
  
    // Returns the last entered context or an empty handle if no
    // contexts have been entered.
    inline Handle<Context> LastEnteredContext();
  
    inline void EnterMicrotaskContext(Handle<Context> context);
    inline void LeaveMicrotaskContext();
    inline Handle<Context> MicrotaskContext();
    inline bool MicrotaskContextIsLastEnteredContext() const {
      return microtask_context_ &&
             entered_context_count_during_microtasks_ == entered_contexts_.size();
    }
  
    inline void SaveContext(Context* context);
    inline Context* RestoreContext();
    inline bool HasSavedContexts();
  
    inline DetachableVector<Object**>* blocks() { return &blocks_; }
    Isolate* isolate() const { return isolate_; }
  
    void ReturnBlock(Object** block) {
      DCHECK_NOT_NULL(block);
      if (spare_ != nullptr) DeleteArray(spare_);
      spare_ = block;
    }
  
   private:
    void ResetAfterArchive() {
      blocks_.detach();
      entered_contexts_.detach();
      saved_contexts_.detach();
      microtask_context_ = nullptr;
      entered_context_count_during_microtasks_ = 0;
      spare_ = nullptr;
      last_handle_before_deferred_block_ = nullptr;
      call_depth_ = 0;
    }
  
    void Free() {
      DCHECK(blocks_.empty());
      DCHECK(entered_contexts_.empty());
      DCHECK(saved_contexts_.empty());
      DCHECK(!microtask_context_);
  
      blocks_.free();
      entered_contexts_.free();
      saved_contexts_.free();
      if (spare_ != nullptr) {
        DeleteArray(spare_);
        spare_ = nullptr;
      }
      DCHECK_EQ(call_depth_, 0);
    }
  
    void BeginDeferredScope();
    DeferredHandles* Detach(Object** prev_limit);
  
    Isolate* isolate_;
    DetachableVector<Object**> blocks_;
    // Used as a stack to keep track of entered contexts.
    DetachableVector<Context*> entered_contexts_;
    // Used as a stack to keep track of saved contexts.
    DetachableVector<Context*> saved_contexts_;
    Context* microtask_context_;
    Object** spare_;
    int call_depth_;
    int microtasks_depth_;
    int microtasks_suppressions_;
    size_t entered_context_count_during_microtasks_;
  #ifdef DEBUG
    int debug_microtasks_depth_;
  #endif
    v8::MicrotasksPolicy microtasks_policy_;
    Object** last_handle_before_deferred_block_;
    // This is only used for threading support.
    HandleScopeData handle_scope_data_;
  
    void IterateThis(RootVisitor* v);
    char* RestoreThreadHelper(char* from);
    char* ArchiveThreadHelper(char* to);
  
    friend class DeferredHandles;
    friend class DeferredHandleScope;
  
    DISALLOW_COPY_AND_ASSIGN(HandleScopeImplementer);
  };
  
  
  const int kHandleBlockSize = v8::internal::KB - 2;  // fit in one page
  
  
  void HandleScopeImplementer::set_microtasks_policy(
      v8::MicrotasksPolicy policy) {
    microtasks_policy_ = policy;
  }
  
  
  v8::MicrotasksPolicy HandleScopeImplementer::microtasks_policy() const {
    return microtasks_policy_;
  }
  
  
  void HandleScopeImplementer::SaveContext(Context* context) {
    saved_contexts_.push_back(context);
  }
  
  
  Context* HandleScopeImplementer::RestoreContext() {
    Context* last_context = saved_contexts_.back();
    saved_contexts_.pop_back();
    return last_context;
  }
  
  
  bool HandleScopeImplementer::HasSavedContexts() {
    return !saved_contexts_.empty();
  }
  
  
  void HandleScopeImplementer::EnterContext(Handle<Context> context) {
    entered_contexts_.push_back(*context);
  }
  
  void HandleScopeImplementer::LeaveContext() { entered_contexts_.pop_back(); }
  
  bool HandleScopeImplementer::LastEnteredContextWas(Handle<Context> context) {
    return !entered_contexts_.empty() && entered_contexts_.back() == *context;
  }
  
  
  Handle<Context> HandleScopeImplementer::LastEnteredContext() {
    if (entered_contexts_.empty()) return Handle<Context>::null();
    return Handle<Context>(entered_contexts_.back());
  }
  
  void HandleScopeImplementer::EnterMicrotaskContext(Handle<Context> context) {
    DCHECK(!microtask_context_);
    microtask_context_ = *context;
    entered_context_count_during_microtasks_ = entered_contexts_.size();
  }
  
  void HandleScopeImplementer::LeaveMicrotaskContext() {
    DCHECK(microtask_context_);
    microtask_context_ = nullptr;
    entered_context_count_during_microtasks_ = 0;
  }
  
  Handle<Context> HandleScopeImplementer::MicrotaskContext() {
    if (microtask_context_) return Handle<Context>(microtask_context_);
    return Handle<Context>::null();
  }
  
  // If there's a spare block, use it for growing the current scope.
  internal::Object** HandleScopeImplementer::GetSpareOrNewBlock() {
    internal::Object** block =
        (spare_ != nullptr) ? spare_
                            : NewArray<internal::Object*>(kHandleBlockSize);
    spare_ = nullptr;
    return block;
  }
  
  
  void HandleScopeImplementer::DeleteExtensions(internal::Object** prev_limit) {
    while (!blocks_.empty()) {
      internal::Object** block_start = blocks_.back();
      internal::Object** block_limit = block_start + kHandleBlockSize;
  
      // SealHandleScope may make the prev_limit to point inside the block.
      if (block_start <= prev_limit && prev_limit <= block_limit) {
  #ifdef ENABLE_HANDLE_ZAPPING
        internal::HandleScope::ZapRange(prev_limit, block_limit);
  #endif
        break;
      }
  
      blocks_.pop_back();
  #ifdef ENABLE_HANDLE_ZAPPING
      internal::HandleScope::ZapRange(block_start, block_limit);
  #endif
      if (spare_ != nullptr) {
        DeleteArray(spare_);
      }
      spare_ = block_start;
    }
    DCHECK((blocks_.empty() && prev_limit == nullptr) ||
           (!blocks_.empty() && prev_limit != nullptr));
  }
  
  // Interceptor functions called from generated inline caches to notify
  // CPU profiler that external callbacks are invoked.
  void InvokeAccessorGetterCallback(
      v8::Local<v8::Name> property,
      const v8::PropertyCallbackInfo<v8::Value>& info,
      v8::AccessorNameGetterCallback getter);
  
  void InvokeFunctionCallback(const v8::FunctionCallbackInfo<v8::Value>& info,
                              v8::FunctionCallback callback);
  
  class Testing {
   public:
    static v8::Testing::StressType stress_type() { return stress_type_; }
    static void set_stress_type(v8::Testing::StressType stress_type) {
      stress_type_ = stress_type;
    }
  
   private:
    static v8::Testing::StressType stress_type_;
  };
  
  }  // namespace internal
  }  // namespace v8
  
  #endif  // V8_API_H_
  