base_object.h

// Copyright Joyent, Inc. and other Node contributors.
//
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// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
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// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
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#ifndef SRC_BASE_OBJECT_H_
#define SRC_BASE_OBJECT_H_

#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#include "memory_tracker.h"
#include "v8.h"
#include <type_traits>  // std::remove_reference

namespace node {

class Environment;

class BaseObject : public MemoryRetainer {
 public:
  // Associates this object with `object`. It uses the 0th internal field for
  // that, and in particular aborts if there is no such field.
  inline BaseObject(Environment* env, v8::Local<v8::Object> object);
  inline ~BaseObject() override;

  BaseObject() = delete;

  // Returns the wrapped object.  Returns an empty handle when
  // persistent.IsEmpty() is true.
  inline v8::Local<v8::Object> object() const;

  // Same as the above, except it additionally verifies that this object
  // is associated with the passed Isolate in debug mode.
  inline v8::Local<v8::Object> object(v8::Isolate* isolate) const;

  inline v8::Global<v8::Object>& persistent();

  inline Environment* env() const;

  // Get a BaseObject* pointer, or subclass pointer, for the JS object that
  // was also passed to the `BaseObject()` constructor initially.
  // This may return `nullptr` if the C++ object has not been constructed yet,
  // e.g. when the JS object used `MakeLazilyInitializedJSTemplate`.
  static inline BaseObject* FromJSObject(v8::Local<v8::Object> object);
  template <typename T>
  static inline T* FromJSObject(v8::Local<v8::Object> object);

  // Make the `v8::Global` a weak reference and, `delete` this object once
  // the JS object has been garbage collected.
  inline void MakeWeak();

  // Undo `MakeWeak()`, i.e. turn this into a strong reference.
  inline void ClearWeak();

  // Utility to create a FunctionTemplate with one internal field (used for
  // the `BaseObject*` pointer) and a constructor that initializes that field
  // to `nullptr`.
  static inline v8::Local<v8::FunctionTemplate> MakeLazilyInitializedJSTemplate(
      Environment* env);

  // Setter/Getter pair for internal fields that can be passed to SetAccessor.
  template <int Field>
  static void InternalFieldGet(v8::Local<v8::String> property,
                               const v8::PropertyCallbackInfo<v8::Value>& info);
  template <int Field, bool (v8::Value::* typecheck)() const>
  static void InternalFieldSet(v8::Local<v8::String> property,
                               v8::Local<v8::Value> value,
                               const v8::PropertyCallbackInfo<void>& info);

  // This is a bit of a hack. See the override in async_wrap.cc for details.
  virtual bool IsDoneInitializing() const;

 protected:
  // Can be used to avoid the automatic object deletion when the Environment
  // exits, for example when this object is owned and deleted by another
  // BaseObject at that point.
  inline void RemoveCleanupHook();

 private:
  v8::Local<v8::Object> WrappedObject() const override;
  static void DeleteMe(void* data);

  // persistent_handle_ needs to be at a fixed offset from the start of the
  // class because it is used by src/node_postmortem_metadata.cc to calculate
  // offsets and generate debug symbols for BaseObject, which assumes that the
  // position of members in memory are predictable. For more information please
  // refer to `doc/guides/node-postmortem-support.md`
  friend int GenDebugSymbols();
  friend class CleanupHookCallback;

  v8::Global<v8::Object> persistent_handle_;
  Environment* env_;
};


// Global alias for FromJSObject() to avoid churn.
template <typename T>
inline T* Unwrap(v8::Local<v8::Object> obj) {
  return BaseObject::FromJSObject<T>(obj);
}


#define ASSIGN_OR_RETURN_UNWRAP(ptr, obj, ...)                                \
  do {                                                                        \
    *ptr = static_cast<typename std::remove_reference<decltype(*ptr)>::type>( \
        BaseObject::FromJSObject(obj));                                       \
    if (*ptr == nullptr)                                                      \
      return __VA_ARGS__;                                                     \
  } while (0)

}  // namespace node

#endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#endif  // SRC_BASE_OBJECT_H_