GCC Code Coverage Report
Directory: ./ Exec Total Coverage
File: base_object.h Lines: 2 3 66.7 %
Date: 2021-10-05 04:12:38 Branches: 0 0 - %

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// Copyright Joyent, Inc. and other Node contributors.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a
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// copy of this software and associated documentation files (the
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// "Software"), to deal in the Software without restriction, including
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// without limitation the rights to use, copy, modify, merge, publish,
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// distribute, sublicense, and/or sell copies of the Software, and to permit
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// persons to whom the Software is furnished to do so, subject to the
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// following conditions:
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//
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// The above copyright notice and this permission notice shall be included
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// in all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
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// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
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// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
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// USE OR OTHER DEALINGS IN THE SOFTWARE.
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#ifndef SRC_BASE_OBJECT_H_
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#define SRC_BASE_OBJECT_H_
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#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
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#include <type_traits>  // std::remove_reference
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#include "memory_tracker.h"
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#include "v8.h"
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namespace node {
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class Environment;
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template <typename T, bool kIsWeak>
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class BaseObjectPtrImpl;
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namespace worker {
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class TransferData;
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}
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class BaseObject : public MemoryRetainer {
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 public:
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  enum InternalFields { kSlot, kInternalFieldCount };
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  // Associates this object with `object`. It uses the 0th internal field for
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  // that, and in particular aborts if there is no such field.
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  inline BaseObject(Environment* env, v8::Local<v8::Object> object);
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  inline ~BaseObject() override;
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  BaseObject() = delete;
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  // Returns the wrapped object.  Returns an empty handle when
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  // persistent.IsEmpty() is true.
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  inline v8::Local<v8::Object> object() const;
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  // Same as the above, except it additionally verifies that this object
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  // is associated with the passed Isolate in debug mode.
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  inline v8::Local<v8::Object> object(v8::Isolate* isolate) const;
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  inline v8::Global<v8::Object>& persistent();
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  inline Environment* env() const;
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  // Get a BaseObject* pointer, or subclass pointer, for the JS object that
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  // was also passed to the `BaseObject()` constructor initially.
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  // This may return `nullptr` if the C++ object has not been constructed yet,
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  // e.g. when the JS object used `MakeLazilyInitializedJSTemplate`.
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  static inline void LazilyInitializedJSTemplateConstructor(
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      const v8::FunctionCallbackInfo<v8::Value>& args);
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  static inline BaseObject* FromJSObject(v8::Local<v8::Value> object);
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  template <typename T>
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  static inline T* FromJSObject(v8::Local<v8::Value> object);
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  // Make the `v8::Global` a weak reference and, `delete` this object once
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  // the JS object has been garbage collected and there are no (strong)
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  // BaseObjectPtr references to it.
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  inline void MakeWeak();
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  // Undo `MakeWeak()`, i.e. turn this into a strong reference that is a GC
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  // root and will not be touched by the garbage collector.
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  inline void ClearWeak();
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  // Reports whether this BaseObject is using a weak reference or detached,
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  // i.e. whether is can be deleted by GC once no strong BaseObjectPtrs refer
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  // to it anymore.
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  inline bool IsWeakOrDetached() const;
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  // Utility to create a FunctionTemplate with one internal field (used for
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  // the `BaseObject*` pointer) and a constructor that initializes that field
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  // to `nullptr`.
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  static inline v8::Local<v8::FunctionTemplate> MakeLazilyInitializedJSTemplate(
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      Environment* env);
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  // Setter/Getter pair for internal fields that can be passed to SetAccessor.
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  template <int Field>
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  static void InternalFieldGet(v8::Local<v8::String> property,
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                               const v8::PropertyCallbackInfo<v8::Value>& info);
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  template <int Field, bool (v8::Value::*typecheck)() const>
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  static void InternalFieldSet(v8::Local<v8::String> property,
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                               v8::Local<v8::Value> value,
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                               const v8::PropertyCallbackInfo<void>& info);
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  // This is a bit of a hack. See the override in async_wrap.cc for details.
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  virtual bool IsDoneInitializing() const;
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  // Can be used to avoid this object keeping itself alive as a GC root
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  // indefinitely, for example when this object is owned and deleted by another
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  // BaseObject once that is torn down. This can only be called when there is
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  // a BaseObjectPtr to this object.
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  inline void Detach();
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  static v8::Local<v8::FunctionTemplate> GetConstructorTemplate(
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      Environment* env);
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  // Interface for transferring BaseObject instances using the .postMessage()
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  // method of MessagePorts (and, by extension, Workers).
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  // GetTransferMode() returns a transfer mode that indicates how to deal with
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  // the current object:
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  // - kUntransferable:
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  //     No transfer is possible, either because this type of BaseObject does
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  //     not know how to be transferred, or because it is not in a state in
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  //     which it is possible to do so (e.g. because it has already been
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  //     transferred).
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  // - kTransferable:
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  //     This object can be transferred in a destructive fashion, i.e. will be
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  //     rendered unusable on the sending side of the channel in the process
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  //     of being transferred. (In C++ this would be referred to as movable but
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  //     not copyable.) Objects of this type need to be listed in the
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  //     `transferList` argument of the relevant postMessage() call in order to
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  //     make sure that they are not accidentally destroyed on the sending side.
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  //     TransferForMessaging() will be called to get a representation of the
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  //     object that is used for subsequent deserialization.
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  //     The NestedTransferables() method can be used to transfer other objects
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  //     along with this one, if a situation requires it.
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  // - kCloneable:
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  //     This object can be cloned without being modified.
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  //     CloneForMessaging() will be called to get a representation of the
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  //     object that is used for subsequent deserialization, unless the
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  //     object is listed in transferList, in which case TransferForMessaging()
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  //     is attempted first.
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  // After a successful clone, FinalizeTransferRead() is called on the receiving
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  // end, and can read deserialize JS data possibly serialized by a previous
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  // FinalizeTransferWrite() call.
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  enum class TransferMode {
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    kUntransferable,
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    kTransferable,
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    kCloneable
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  };
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  virtual TransferMode GetTransferMode() const;
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  virtual std::unique_ptr<worker::TransferData> TransferForMessaging();
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  virtual std::unique_ptr<worker::TransferData> CloneForMessaging() const;
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  virtual v8::Maybe<std::vector<BaseObjectPtrImpl<BaseObject, false>>>
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      NestedTransferables() const;
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  virtual v8::Maybe<bool> FinalizeTransferRead(
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      v8::Local<v8::Context> context, v8::ValueDeserializer* deserializer);
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  // Indicates whether this object is expected to use a strong reference during
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  // a clean process exit (due to an empty event loop).
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  virtual bool IsNotIndicativeOfMemoryLeakAtExit() const;
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  virtual inline void OnGCCollect();
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  virtual inline bool is_snapshotable() const { return false; }
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 private:
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  v8::Local<v8::Object> WrappedObject() const override;
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  bool IsRootNode() const override;
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  static void DeleteMe(void* data);
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  // persistent_handle_ needs to be at a fixed offset from the start of the
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  // class because it is used by src/node_postmortem_metadata.cc to calculate
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  // offsets and generate debug symbols for BaseObject, which assumes that the
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  // position of members in memory are predictable. For more information please
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  // refer to `doc/guides/node-postmortem-support.md`
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  friend int GenDebugSymbols();
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  friend class CleanupHookCallback;
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  template <typename T, bool kIsWeak>
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  friend class BaseObjectPtrImpl;
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  v8::Global<v8::Object> persistent_handle_;
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  // Metadata that is associated with this BaseObject if there are BaseObjectPtr
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  // or BaseObjectWeakPtr references to it.
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  // This object is deleted when the BaseObject itself is destroyed, and there
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  // are no weak references to it.
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  struct PointerData {
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    // Number of BaseObjectPtr instances that refer to this object. If this
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    // is non-zero, the BaseObject is always a GC root and will not be destroyed
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    // during cleanup until the count drops to zero again.
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    unsigned int strong_ptr_count = 0;
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    // Number of BaseObjectWeakPtr instances that refer to this object.
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    unsigned int weak_ptr_count = 0;
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    // Indicates whether MakeWeak() has been called.
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    bool wants_weak_jsobj = false;
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    // Indicates whether Detach() has been called. If that is the case, this
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    // object will be destroyed once the strong pointer count drops to zero.
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    bool is_detached = false;
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    // Reference to the original BaseObject. This is used by weak pointers.
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    BaseObject* self = nullptr;
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  };
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  inline bool has_pointer_data() const;
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  // This creates a PointerData struct if none was associated with this
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  // BaseObject before.
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  inline PointerData* pointer_data();
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  // Functions that adjust the strong pointer count.
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  inline void decrease_refcount();
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  inline void increase_refcount();
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  Environment* env_;
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  PointerData* pointer_data_ = nullptr;
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};
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// Global alias for FromJSObject() to avoid churn.
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template <typename T>
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inline T* Unwrap(v8::Local<v8::Value> obj) {
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  return BaseObject::FromJSObject<T>(obj);
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}
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#define ASSIGN_OR_RETURN_UNWRAP(ptr, obj, ...)                                 \
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  do {                                                                         \
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    *ptr = static_cast<typename std::remove_reference<decltype(*ptr)>::type>(  \
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        BaseObject::FromJSObject(obj));                                        \
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    if (*ptr == nullptr) return __VA_ARGS__;                                   \
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  } while (0)
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// Implementation of a generic strong or weak pointer to a BaseObject.
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// If strong, this will keep the target BaseObject alive regardless of other
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// circumstances such as the GC or Environment cleanup.
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// If weak, destruction behaviour is not affected, but the pointer will be
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// reset to nullptr once the BaseObject is destroyed.
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// The API matches std::shared_ptr closely.
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template <typename T, bool kIsWeak>
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class BaseObjectPtrImpl final {
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 public:
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  inline BaseObjectPtrImpl();
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  inline ~BaseObjectPtrImpl();
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  inline explicit BaseObjectPtrImpl(T* target);
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  // Copy and move constructors. Note that the templated version is not a copy
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  // or move constructor in the C++ sense of the word, so an identical
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  // untemplated version is provided.
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  template <typename U, bool kW>
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  inline BaseObjectPtrImpl(const BaseObjectPtrImpl<U, kW>& other);
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  inline BaseObjectPtrImpl(const BaseObjectPtrImpl& other);
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  template <typename U, bool kW>
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  inline BaseObjectPtrImpl& operator=(const BaseObjectPtrImpl<U, kW>& other);
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  inline BaseObjectPtrImpl& operator=(const BaseObjectPtrImpl& other);
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  inline BaseObjectPtrImpl(BaseObjectPtrImpl&& other);
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  inline BaseObjectPtrImpl& operator=(BaseObjectPtrImpl&& other);
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  inline void reset(T* ptr = nullptr);
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  inline T* get() const;
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  inline T& operator*() const;
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  inline T* operator->() const;
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  inline operator bool() const;
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  template <typename U, bool kW>
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  inline bool operator ==(const BaseObjectPtrImpl<U, kW>& other) const;
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  template <typename U, bool kW>
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  inline bool operator !=(const BaseObjectPtrImpl<U, kW>& other) const;
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 private:
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  union {
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    BaseObject* target;                     // Used for strong pointers.
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    BaseObject::PointerData* pointer_data;  // Used for weak pointers.
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  } data_;
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  inline BaseObject* get_base_object() const;
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  inline BaseObject::PointerData* pointer_data() const;
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};
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template <typename T>
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using BaseObjectPtr = BaseObjectPtrImpl<T, false>;
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template <typename T>
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using BaseObjectWeakPtr = BaseObjectPtrImpl<T, true>;
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// Create a BaseObject instance and return a pointer to it.
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// This variant leaves the object as a GC root by default.
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template <typename T, typename... Args>
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inline BaseObjectPtr<T> MakeBaseObject(Args&&... args);
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// Create a BaseObject instance and return a pointer to it.
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// This variant detaches the object by default, meaning that the caller fully
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// owns it, and once the last BaseObjectPtr to it is destroyed, the object
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// itself is also destroyed.
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template <typename T, typename... Args>
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inline BaseObjectPtr<T> MakeDetachedBaseObject(Args&&... args);
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}  // namespace node
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#endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
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#endif  // SRC_BASE_OBJECT_H_