// Copyright Joyent, Inc. and other Node contributors.

//

// Permission is hereby granted, free of charge, to any person obtaining a

// copy of this software and associated documentation files (the

// "Software"), to deal in the Software without restriction, including

// without limitation the rights to use, copy, modify, merge, publish,

// distribute, sublicense, and/or sell copies of the Software, and to permit

// persons to whom the Software is furnished to do so, subject to the

// following conditions:

//

// The above copyright notice and this permission notice shall be included

// in all copies or substantial portions of the Software.

//

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS

// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN

// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,

// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR

// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE

// USE OR OTHER DEALINGS IN THE SOFTWARE.

#ifndef SRC_BASE_OBJECT_H_

#define SRC_BASE_OBJECT_H_

#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#include <type_traits>  // std::remove_reference

#include "memory_tracker.h"

#include "v8.h"

namespace node {

class Environment;

template <typename T, bool kIsWeak>

class BaseObjectPtrImpl;

namespace worker {

class TransferData;

}

extern uint16_t kNodeEmbedderId;

class BaseObject : public MemoryRetainer {

 public:

  enum InternalFields { kEmbedderType, kSlot, kInternalFieldCount };

  // Associates this object with `object`. It uses the 1st internal field for

  // that, and in particular aborts if there is no such field.

  BaseObject(Environment* env, v8::Local<v8::Object> object);

  ~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 void LazilyInitializedJSTemplateConstructor(

      const v8::FunctionCallbackInfo<v8::Value>& args);

  static inline BaseObject* FromJSObject(v8::Local<v8::Value> object);

  template <typename T>

  static inline T* FromJSObject(v8::Local<v8::Value> object);

  // Make the `v8::Global` a weak reference and, `delete` this object once

  // the JS object has been garbage collected and there are no (strong)

  // BaseObjectPtr references to it.

  void MakeWeak();

  // Undo `MakeWeak()`, i.e. turn this into a strong reference that is a GC

  // root and will not be touched by the garbage collector.

  inline void ClearWeak();

  // Reports whether this BaseObject is using a weak reference or detached,

  // i.e. whether is can be deleted by GC once no strong BaseObjectPtrs refer

  // to it anymore.

  inline bool IsWeakOrDetached() const;

  // Utility to create a FunctionTemplate with one internal field (used for

  // the `BaseObject*` pointer) and a constructor that initializes that field

  // to `nullptr`.

  static 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;

  // Can be used to avoid this object keeping itself alive as a GC root

  // indefinitely, for example when this object is owned and deleted by another

  // BaseObject once that is torn down. This can only be called when there is

  // a BaseObjectPtr to this object.

  inline void Detach();

  static v8::Local<v8::FunctionTemplate> GetConstructorTemplate(

      Environment* env);

  // Interface for transferring BaseObject instances using the .postMessage()

  // method of MessagePorts (and, by extension, Workers).

  // GetTransferMode() returns a transfer mode that indicates how to deal with

  // the current object:

  // - kUntransferable:

  //     No transfer is possible, either because this type of BaseObject does

  //     not know how to be transferred, or because it is not in a state in

  //     which it is possible to do so (e.g. because it has already been

  //     transferred).

  // - kTransferable:

  //     This object can be transferred in a destructive fashion, i.e. will be

  //     rendered unusable on the sending side of the channel in the process

  //     of being transferred. (In C++ this would be referred to as movable but

  //     not copyable.) Objects of this type need to be listed in the

  //     `transferList` argument of the relevant postMessage() call in order to

  //     make sure that they are not accidentally destroyed on the sending side.

  //     TransferForMessaging() will be called to get a representation of the

  //     object that is used for subsequent deserialization.

  //     The NestedTransferables() method can be used to transfer other objects

  //     along with this one, if a situation requires it.

  // - kCloneable:

  //     This object can be cloned without being modified.

  //     CloneForMessaging() will be called to get a representation of the

  //     object that is used for subsequent deserialization, unless the

  //     object is listed in transferList, in which case TransferForMessaging()

  //     is attempted first.

  // After a successful clone, FinalizeTransferRead() is called on the receiving

  // end, and can read deserialize JS data possibly serialized by a previous

  // FinalizeTransferWrite() call.

  enum class TransferMode {

    kUntransferable,

    kTransferable,

    kCloneable

  };

  virtual TransferMode GetTransferMode() const;

  virtual std::unique_ptr<worker::TransferData> TransferForMessaging();

  virtual std::unique_ptr<worker::TransferData> CloneForMessaging() const;

  virtual v8::Maybe<std::vector<BaseObjectPtrImpl<BaseObject, false>>>

      NestedTransferables() const;

  virtual v8::Maybe<bool> FinalizeTransferRead(

      v8::Local<v8::Context> context, v8::ValueDeserializer* deserializer);

  // Indicates whether this object is expected to use a strong reference during

  // a clean process exit (due to an empty event loop).

  virtual bool IsNotIndicativeOfMemoryLeakAtExit() const;

  virtual inline void OnGCCollect();

 private:

  v8::Local<v8::Object> WrappedObject() const override;

  bool IsRootNode() 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/contributing/node-postmortem-support.md`

  friend int GenDebugSymbols();

  friend class CleanupHookCallback;

  template <typename T, bool kIsWeak>

  friend class BaseObjectPtrImpl;

  v8::Global<v8::Object> persistent_handle_;

  // Metadata that is associated with this BaseObject if there are BaseObjectPtr

  // or BaseObjectWeakPtr references to it.

  // This object is deleted when the BaseObject itself is destroyed, and there

  // are no weak references to it.

  struct PointerData {

    // Number of BaseObjectPtr instances that refer to this object. If this

    // is non-zero, the BaseObject is always a GC root and will not be destroyed

    // during cleanup until the count drops to zero again.

    unsigned int strong_ptr_count = 0;

    // Number of BaseObjectWeakPtr instances that refer to this object.

    unsigned int weak_ptr_count = 0;

    // Indicates whether MakeWeak() has been called.

    bool wants_weak_jsobj = false;

    // Indicates whether Detach() has been called. If that is the case, this

    // object will be destroyed once the strong pointer count drops to zero.

    bool is_detached = false;

    // Reference to the original BaseObject. This is used by weak pointers.

    BaseObject* self = nullptr;

  };

  inline bool has_pointer_data() const;

  // This creates a PointerData struct if none was associated with this

  // BaseObject before.

  PointerData* pointer_data();

  // Functions that adjust the strong pointer count.

  void decrease_refcount();

  void increase_refcount();

  Environment* env_;

  PointerData* pointer_data_ = nullptr;

};

// Global alias for FromJSObject() to avoid churn.

template <typename T>

}

#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)

// Implementation of a generic strong or weak pointer to a BaseObject.

// If strong, this will keep the target BaseObject alive regardless of other

// circumstances such as the GC or Environment cleanup.

// If weak, destruction behaviour is not affected, but the pointer will be

// reset to nullptr once the BaseObject is destroyed.

// The API matches std::shared_ptr closely.

template <typename T, bool kIsWeak>

class BaseObjectPtrImpl final {

 public:

  inline BaseObjectPtrImpl();

  inline ~BaseObjectPtrImpl();

  inline explicit BaseObjectPtrImpl(T* target);

  // Copy and move constructors. Note that the templated version is not a copy

  // or move constructor in the C++ sense of the word, so an identical

  // untemplated version is provided.

  template <typename U, bool kW>

  inline BaseObjectPtrImpl(const BaseObjectPtrImpl<U, kW>& other);

  inline BaseObjectPtrImpl(const BaseObjectPtrImpl& other);

  template <typename U, bool kW>

  inline BaseObjectPtrImpl& operator=(const BaseObjectPtrImpl<U, kW>& other);

  inline BaseObjectPtrImpl& operator=(const BaseObjectPtrImpl& other);

  inline BaseObjectPtrImpl(BaseObjectPtrImpl&& other);

  inline BaseObjectPtrImpl& operator=(BaseObjectPtrImpl&& other);

  inline void reset(T* ptr = nullptr);

  inline T* get() const;

  inline T& operator*() const;

  inline T* operator->() const;

  inline operator bool() const;

  template <typename U, bool kW>

  inline bool operator ==(const BaseObjectPtrImpl<U, kW>& other) const;

  template <typename U, bool kW>

  inline bool operator !=(const BaseObjectPtrImpl<U, kW>& other) const;

 private:

  union {

    BaseObject* target;                     // Used for strong pointers.

    BaseObject::PointerData* pointer_data;  // Used for weak pointers.

  } data_;

  inline BaseObject* get_base_object() const;

  inline BaseObject::PointerData* pointer_data() const;

};

template <typename T>

using BaseObjectPtr = BaseObjectPtrImpl<T, false>;

template <typename T>

using BaseObjectWeakPtr = BaseObjectPtrImpl<T, true>;

// Create a BaseObject instance and return a pointer to it.

// This variant leaves the object as a GC root by default.

template <typename T, typename... Args>

inline BaseObjectPtr<T> MakeBaseObject(Args&&... args);

// Create a BaseObject instance and return a pointer to it.

// This variant detaches the object by default, meaning that the caller fully

// owns it, and once the last BaseObjectPtr to it is destroyed, the object

// itself is also destroyed.

template <typename T, typename... Args>

inline BaseObjectPtr<T> MakeDetachedBaseObject(Args&&... args);

}  // namespace node

#endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#endif  // SRC_BASE_OBJECT_H_