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// 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 "base_object_types.h"

#include "memory_tracker.h"

#include "node_v8_embedder.h"

#include "util.h"

#include "v8.h"

namespace node {

class Environment;

class IsolateData;

class Realm;

template <typename T, bool kIsWeak>

class BaseObjectPtrImpl;

namespace worker {

class TransferData;

}

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.

// This is the designated constructor.

BaseObject(Realm* realm, v8::Local<v8::Object> object);

// Convenient constructor for constructing BaseObject in the principal realm.

inline 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;

inline Realm* realm() 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 void SetInternalFields(IsolateData* isolate_data,

v8::Local<v8::Object> object,

void* slot);

static inline bool IsBaseObject(IsolateData* isolate_data,

v8::Local<v8::Object> object);

static inline void TagBaseObject(IsolateData* isolate_data,

v8::Local<v8::Object> object);

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);

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

template <typename T>

static inline T* Unwrap(v8::Local<v8::Value> obj) {

return BaseObject::FromJSObject<T>(obj);

}

// 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(

IsolateData* isolate, int internal_field_count = kInternalFieldCount);

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

Environment* env, int internal_field_count = kInternalFieldCount);

// Setter/Getter pair for internal fields that can be passed to SetAccessor.

template <int Field>

static void InternalFieldGet(const v8::FunctionCallbackInfo<v8::Value>& args);

template <int Field, bool (v8::Value::*typecheck)() const>

static void InternalFieldSet(const v8::FunctionCallbackInfo<v8::Value>& args);

// 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();

// 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:

// - kDisallowCloneAndTransfer:

// No transfer or clone 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 and is kTransferable, in which case

// TransferForMessaging() is attempted first.

// - kTransferableAndCloneable:

// This object can be transferred or cloned.

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

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

// FinalizeTransferWrite() call.

// By default, a BaseObject is kDisallowCloneAndTransfer and a JS Object is

// kCloneable unless otherwise specified.

enum TransferMode : uint32_t {

kDisallowCloneAndTransfer = 0,

kTransferable = 1 << 0,

kCloneable = 1 << 1,

kTransferableAndCloneable = 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<void> 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();

virtual inline bool is_snapshotable() const { return false; }

private:

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

void DeleteMe();

// 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 CleanupQueue;

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();

Realm* realm_;

PointerData* pointer_data_ = nullptr;

ListNode<BaseObject> base_object_list_node_;

friend class BaseObjectList;

};

class BaseObjectList

: public ListHead<BaseObject, &BaseObject::base_object_list_node_>,

public MemoryRetainer {

public:

void Cleanup();

SET_MEMORY_INFO_NAME(BaseObjectList)

SET_SELF_SIZE(BaseObjectList)

void MemoryInfo(node::MemoryTracker* tracker) const override;

};

#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. However, this class is not thread

// safe, that is, we can't have different BaseObjectPtrImpl instances in

// different threads referring to the same BaseObject instance.

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 BaseObjectPtrImpl(std::nullptr_t);

inline BaseObjectPtrImpl& operator=(std::nullptr_t);

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, bool kIsWeak>

inline static bool operator==(const BaseObjectPtrImpl<T, kIsWeak>,

const std::nullptr_t);

template <typename T, bool kIsWeak>

inline static bool operator==(const std::nullptr_t,

const BaseObjectPtrImpl<T, kIsWeak>);

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 makes the object a weak GC root by default.

template <typename T, typename... Args>

inline BaseObjectWeakPtr<T> MakeWeakBaseObject(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_

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