// Copyright 2021 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 INCLUDE_V8_PERSISTENT_HANDLE_H_
#define INCLUDE_V8_PERSISTENT_HANDLE_H_
#include "v8-internal.h" // NOLINT(build/include_directory)
#include "v8-local-handle.h" // NOLINT(build/include_directory)
#include "v8-weak-callback-info.h" // NOLINT(build/include_directory)
#include "v8config.h" // NOLINT(build/include_directory)
namespace v8 {
class Isolate;
template <class K, class V, class T>
class PersistentValueMapBase;
template <class V, class T>
class PersistentValueVector;
template <class T>
class Global;
template <class T>
class PersistentBase;
template <class K, class V, class T>
class PersistentValueMap;
class Value;
namespace api_internal {
V8_EXPORT internal::Address* Eternalize(v8::Isolate* isolate, Value* handle);
V8_EXPORT internal::Address* CopyGlobalReference(internal::Address* from);
V8_EXPORT void DisposeGlobal(internal::Address* global_handle);
V8_EXPORT void MakeWeak(internal::Address** location_addr);
V8_EXPORT void* ClearWeak(internal::Address* location);
V8_EXPORT void AnnotateStrongRetainer(internal::Address* location,
const char* label);
V8_EXPORT internal::Address* GlobalizeReference(internal::Isolate* isolate,
internal::Address value);
V8_EXPORT void MoveGlobalReference(internal::Address** from,
internal::Address** to);
} // namespace api_internal
/**
* Eternal handles are set-once handles that live for the lifetime of the
* isolate.
*/
template <class T>
class Eternal : public api_internal::IndirectHandleBase {
public:
V8_INLINE Eternal() = default;
template <class S>
V8_INLINE Eternal(Isolate* isolate, Local<S> handle) {
Set(isolate, handle);
}
// Can only be safely called if already set.
V8_INLINE Local<T> Get(Isolate* isolate) const {
// The eternal handle will never go away, so as with the roots, we don't
// even need to open a handle.
return Local<T>::FromSlot(slot());
}
template <class S>
void Set(Isolate* isolate, Local<S> handle) {
static_assert(std::is_base_of<T, S>::value, "type check");
slot() =
api_internal::Eternalize(isolate, *handle.template UnsafeAs<Value>());
}
};
namespace api_internal {
V8_EXPORT void MakeWeak(internal::Address* location, void* data,
WeakCallbackInfo<void>::Callback weak_callback,
WeakCallbackType type);
} // namespace api_internal
/**
* An object reference that is independent of any handle scope. Where
* a Local handle only lives as long as the HandleScope in which it was
* allocated, a PersistentBase handle remains valid until it is explicitly
* disposed using Reset().
*
* A persistent handle contains a reference to a storage cell within
* the V8 engine which holds an object value and which is updated by
* the garbage collector whenever the object is moved. A new storage
* cell can be created using the constructor or PersistentBase::Reset and
* existing handles can be disposed using PersistentBase::Reset.
*
*/
template <class T>
class PersistentBase : public api_internal::IndirectHandleBase {
public:
/**
* If non-empty, destroy the underlying storage cell
* IsEmpty() will return true after this call.
*/
V8_INLINE void Reset();
/**
* If non-empty, destroy the underlying storage cell
* and create a new one with the contents of other if other is non empty
*/
template <class S>
V8_INLINE void Reset(Isolate* isolate, const Local<S>& other);
/**
* If non-empty, destroy the underlying storage cell
* and create a new one with the contents of other if other is non empty
*/
template <class S>
V8_INLINE void Reset(Isolate* isolate, const PersistentBase<S>& other);
V8_INLINE Local<T> Get(Isolate* isolate) const {
return Local<T>::New(isolate, *this);
}
template <class S>
V8_INLINE bool operator==(const PersistentBase<S>& that) const {
return internal::HandleHelper::EqualHandles(*this, that);
}
template <class S>
V8_INLINE bool operator==(const Local<S>& that) const {
return internal::HandleHelper::EqualHandles(*this, that);
}
template <class S>
V8_INLINE bool operator!=(const PersistentBase<S>& that) const {
return !operator==(that);
}
template <class S>
V8_INLINE bool operator!=(const Local<S>& that) const {
return !operator==(that);
}
/**
* Install a finalization callback on this object.
* NOTE: There is no guarantee as to *when* or even *if* the callback is
* invoked. The invocation is performed solely on a best effort basis.
* As always, GC-based finalization should *not* be relied upon for any
* critical form of resource management!
*
* The callback is supposed to reset the handle. No further V8 API may be
* called in this callback. In case additional work involving V8 needs to be
* done, a second callback can be scheduled using
* WeakCallbackInfo<void>::SetSecondPassCallback.
*/
template <typename P>
V8_INLINE void SetWeak(P* parameter,
typename WeakCallbackInfo<P>::Callback callback,
WeakCallbackType type);
/**
* Turns this handle into a weak phantom handle without finalization callback.
* The handle will be reset automatically when the garbage collector detects
* that the object is no longer reachable.
*/
V8_INLINE void SetWeak();
template <typename P>
V8_INLINE P* ClearWeak();
// TODO(dcarney): remove this.
V8_INLINE void ClearWeak() { ClearWeak<void>(); }
/**
* Annotates the strong handle with the given label, which is then used by the
* heap snapshot generator as a name of the edge from the root to the handle.
* The function does not take ownership of the label and assumes that the
* label is valid as long as the handle is valid.
*/
V8_INLINE void AnnotateStrongRetainer(const char* label);
/** Returns true if the handle's reference is weak. */
V8_INLINE bool IsWeak() const;
/**
* Assigns a wrapper class ID to the handle.
*/
V8_INLINE void SetWrapperClassId(uint16_t class_id);
/**
* Returns the class ID previously assigned to this handle or 0 if no class ID
* was previously assigned.
*/
V8_INLINE uint16_t WrapperClassId() const;
PersistentBase(const PersistentBase& other) = delete;
void operator=(const PersistentBase&) = delete;
private:
friend class Isolate;
friend class Utils;
template <class F>
friend class Local;
template <class F1, class F2>
friend class Persistent;
template <class F>
friend class Global;
template <class F>
friend class PersistentBase;
template <class F>
friend class ReturnValue;
template <class F1, class F2, class F3>
friend class PersistentValueMapBase;
template <class F1, class F2>
friend class PersistentValueVector;
friend class Object;
friend class internal::ValueHelper;
V8_INLINE PersistentBase() = default;
V8_INLINE explicit PersistentBase(internal::Address* location)
: IndirectHandleBase(location) {}
V8_INLINE static internal::Address* New(Isolate* isolate, T* that);
};
/**
* Default traits for Persistent. This class does not allow
* use of the copy constructor or assignment operator.
* At present kResetInDestructor is not set, but that will change in a future
* version.
*/
template <class T>
class NonCopyablePersistentTraits {
public:
using NonCopyablePersistent = Persistent<T, NonCopyablePersistentTraits<T>>;
static const bool kResetInDestructor = false;
template <class S, class M>
V8_INLINE static void Copy(const Persistent<S, M>& source,
NonCopyablePersistent* dest) {
static_assert(sizeof(S) < 0,
"NonCopyablePersistentTraits::Copy is not instantiable");
}
};
/**
* Helper class traits to allow copying and assignment of Persistent.
* This will clone the contents of storage cell, but not any of the flags, etc.
*/
template <class T>
struct CopyablePersistentTraits {
using CopyablePersistent = Persistent<T, CopyablePersistentTraits<T>>;
static const bool kResetInDestructor = true;
template <class S, class M>
static V8_INLINE void Copy(const Persistent<S, M>& source,
CopyablePersistent* dest) {
// do nothing, just allow copy
}
};
/**
* A PersistentBase which allows copy and assignment.
*
* Copy, assignment and destructor behavior is controlled by the traits
* class M.
*
* CAVEAT: Persistent objects do not have proper destruction behavior by default
* and as such will leak the object without explicit clear. Consider using
* `v8::Global` instead which has proper destruction and move semantics.
*/
template <class T, class M>
class Persistent : public PersistentBase<T> {
public:
/**
* A Persistent with no storage cell.
*/
V8_INLINE Persistent() = default;
/**
* Construct a Persistent from a Local.
* When the Local is non-empty, a new storage cell is created
* pointing to the same object, and no flags are set.
*/
template <class S>
V8_INLINE Persistent(Isolate* isolate, Local<S> that)
: PersistentBase<T>(
PersistentBase<T>::New(isolate, that.template value<S>())) {
static_assert(std::is_base_of<T, S>::value, "type check");
}
/**
* Construct a Persistent from a Persistent.
* When the Persistent is non-empty, a new storage cell is created
* pointing to the same object, and no flags are set.
*/
template <class S, class M2>
V8_INLINE Persistent(Isolate* isolate, const Persistent<S, M2>& that)
: PersistentBase<T>(
PersistentBase<T>::New(isolate, that.template value<S>())) {
static_assert(std::is_base_of<T, S>::value, "type check");
}
/**
* The copy constructors and assignment operator create a Persistent
* exactly as the Persistent constructor, but the Copy function from the
* traits class is called, allowing the setting of flags based on the
* copied Persistent.
*/
V8_INLINE Persistent(const Persistent& that) : PersistentBase<T>() {
Copy(that);
}
template <class S, class M2>
V8_INLINE Persistent(const Persistent<S, M2>& that) : PersistentBase<T>() {
Copy(that);
}
V8_INLINE Persistent& operator=(const Persistent& that) {
Copy(that);
return *this;
}
template <class S, class M2>
V8_INLINE Persistent& operator=(const Persistent<S, M2>& that) {
Copy(that);
return *this;
}
/**
* The destructor will dispose the Persistent based on the
* kResetInDestructor flags in the traits class. Since not calling dispose
* can result in a memory leak, it is recommended to always set this flag.
*/
V8_INLINE ~Persistent() {
if (M::kResetInDestructor) this->Reset();
}
// TODO(dcarney): this is pretty useless, fix or remove
template <class S, class M2>
V8_INLINE static Persistent<T, M>& Cast(const Persistent<S, M2>& that) {
#ifdef V8_ENABLE_CHECKS
// If we're going to perform the type check then we have to check
// that the handle isn't empty before doing the checked cast.
if (!that.IsEmpty()) T::Cast(that.template value<S>());
#endif
return reinterpret_cast<Persistent<T, M>&>(
const_cast<Persistent<S, M2>&>(that));
}
// TODO(dcarney): this is pretty useless, fix or remove
template <class S, class M2>
V8_INLINE Persistent<S, M2>& As() const {
return Persistent<S, M2>::Cast(*this);
}
private:
friend class Isolate;
friend class Utils;
template <class F>
friend class Local;
template <class F1, class F2>
friend class Persistent;
template <class F>
friend class ReturnValue;
template <class S, class M2>
V8_INLINE void Copy(const Persistent<S, M2>& that);
};
/**
* A PersistentBase which has move semantics.
*
* Note: Persistent class hierarchy is subject to future changes.
*/
template <class T>
class Global : public PersistentBase<T> {
public:
/**
* A Global with no storage cell.
*/
V8_INLINE Global() = default;
/**
* Construct a Global from a Local.
* When the Local is non-empty, a new storage cell is created
* pointing to the same object, and no flags are set.
*/
template <class S>
V8_INLINE Global(Isolate* isolate, Local<S> that)
: PersistentBase<T>(
PersistentBase<T>::New(isolate, that.template value<S>())) {
static_assert(std::is_base_of<T, S>::value, "type check");
}
/**
* Construct a Global from a PersistentBase.
* When the Persistent is non-empty, a new storage cell is created
* pointing to the same object, and no flags are set.
*/
template <class S>
V8_INLINE Global(Isolate* isolate, const PersistentBase<S>& that)
: PersistentBase<T>(
PersistentBase<T>::New(isolate, that.template value<S>())) {
static_assert(std::is_base_of<T, S>::value, "type check");
}
/**
* Move constructor.
*/
V8_INLINE Global(Global&& other);
V8_INLINE ~Global() { this->Reset(); }
/**
* Move via assignment.
*/
template <class S>
V8_INLINE Global& operator=(Global<S>&& rhs);
/**
* Pass allows returning uniques from functions, etc.
*/
Global Pass() { return static_cast<Global&&>(*this); }
/*
* For compatibility with Chromium's base::Bind (base::Passed).
*/
using MoveOnlyTypeForCPP03 = void;
Global(const Global&) = delete;
void operator=(const Global&) = delete;
private:
template <class F>
friend class ReturnValue;
};
// UniquePersistent is an alias for Global for historical reason.
template <class T>
using UniquePersistent = Global<T>;
/**
* Interface for iterating through all the persistent handles in the heap.
*/
class V8_EXPORT PersistentHandleVisitor {
public:
virtual ~PersistentHandleVisitor() = default;
virtual void VisitPersistentHandle(Persistent<Value>* value,
uint16_t class_id) {}
};
template <class T>
internal::Address* PersistentBase<T>::New(Isolate* isolate, T* that) {
if (internal::ValueHelper::IsEmpty(that)) return nullptr;
return api_internal::GlobalizeReference(
reinterpret_cast<internal::Isolate*>(isolate),
internal::ValueHelper::ValueAsAddress(that));
}
template <class T, class M>
template <class S, class M2>
void Persistent<T, M>::Copy(const Persistent<S, M2>& that) {
static_assert(std::is_base_of<T, S>::value, "type check");
this->Reset();
if (that.IsEmpty()) return;
this->slot() = api_internal::CopyGlobalReference(that.slot());
M::Copy(that, this);
}
template <class T>
bool PersistentBase<T>::IsWeak() const {
using I = internal::Internals;
if (this->IsEmpty()) return false;
return I::GetNodeState(this->slot()) == I::kNodeStateIsWeakValue;
}
template <class T>
void PersistentBase<T>::Reset() {
if (this->IsEmpty()) return;
api_internal::DisposeGlobal(this->slot());
this->Clear();
}
/**
* If non-empty, destroy the underlying storage cell
* and create a new one with the contents of other if other is non empty
*/
template <class T>
template <class S>
void PersistentBase<T>::Reset(Isolate* isolate, const Local<S>& other) {
static_assert(std::is_base_of<T, S>::value, "type check");
Reset();
if (other.IsEmpty()) return;
this->slot() = New(isolate, *other);
}
/**
* If non-empty, destroy the underlying storage cell
* and create a new one with the contents of other if other is non empty
*/
template <class T>
template <class S>
void PersistentBase<T>::Reset(Isolate* isolate,
const PersistentBase<S>& other) {
static_assert(std::is_base_of<T, S>::value, "type check");
Reset();
if (other.IsEmpty()) return;
this->slot() = New(isolate, other.template value<S>());
}
template <class T>
template <typename P>
V8_INLINE void PersistentBase<T>::SetWeak(
P* parameter, typename WeakCallbackInfo<P>::Callback callback,
WeakCallbackType type) {
using Callback = WeakCallbackInfo<void>::Callback;
#if (__GNUC__ >= 8) && !defined(__clang__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wcast-function-type"
#endif
#if __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wcast-function-type"
#endif
api_internal::MakeWeak(this->slot(), parameter,
reinterpret_cast<Callback>(callback), type);
#if __clang__
#pragma clang diagnostic pop
#endif
#if (__GNUC__ >= 8) && !defined(__clang__)
#pragma GCC diagnostic pop
#endif
}
template <class T>
void PersistentBase<T>::SetWeak() {
api_internal::MakeWeak(&this->slot());
}
template <class T>
template <typename P>
P* PersistentBase<T>::ClearWeak() {
return reinterpret_cast<P*>(api_internal::ClearWeak(this->slot()));
}
template <class T>
void PersistentBase<T>::AnnotateStrongRetainer(const char* label) {
api_internal::AnnotateStrongRetainer(this->slot(), label);
}
template <class T>
void PersistentBase<T>::SetWrapperClassId(uint16_t class_id) {
using I = internal::Internals;
if (this->IsEmpty()) return;
uint8_t* addr = reinterpret_cast<uint8_t*>(slot()) + I::kNodeClassIdOffset;
*reinterpret_cast<uint16_t*>(addr) = class_id;
}
template <class T>
uint16_t PersistentBase<T>::WrapperClassId() const {
using I = internal::Internals;
if (this->IsEmpty()) return 0;
uint8_t* addr = reinterpret_cast<uint8_t*>(slot()) + I::kNodeClassIdOffset;
return *reinterpret_cast<uint16_t*>(addr);
}
template <class T>
Global<T>::Global(Global&& other) : PersistentBase<T>(other.slot()) {
if (!other.IsEmpty()) {
api_internal::MoveGlobalReference(&other.slot(), &this->slot());
other.Clear();
}
}
template <class T>
template <class S>
Global<T>& Global<T>::operator=(Global<S>&& rhs) {
static_assert(std::is_base_of<T, S>::value, "type check");
if (this != &rhs) {
this->Reset();
if (!rhs.IsEmpty()) {
this->slot() = rhs.slot();
api_internal::MoveGlobalReference(&rhs.slot(), &this->slot());
rhs.Clear();
}
}
return *this;
}
} // namespace v8
#endif // INCLUDE_V8_PERSISTENT_HANDLE_H_