blob: 9653efa1c2949a3a4af493d97e0114dc8b4cf005 [file] [log] [blame]
// Copyright 2016 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.
#include <memory>
#include "src/execution/isolate.h"
#include "src/handles/global-handles.h"
#include "src/handles/handles.h"
#include "src/heap/factory.h"
#include "src/objects/foreign.h"
namespace v8 {
namespace internal {
// Implements a doubly-linked lists of destructors for the isolate.
struct ManagedPtrDestructor {
// Estimated size of external memory associated with the managed object.
// This is used to adjust the garbage collector's heuristics upon
// allocation and deallocation of a managed object.
size_t estimated_size_ = 0;
ManagedPtrDestructor* prev_ = nullptr;
ManagedPtrDestructor* next_ = nullptr;
void* shared_ptr_ptr_ = nullptr;
void (*destructor_)(void* shared_ptr) = nullptr;
Address* global_handle_location_ = nullptr;
ManagedPtrDestructor(size_t estimated_size, void* shared_ptr_ptr,
void (*destructor)(void*))
: estimated_size_(estimated_size),
destructor_(destructor) {}
// The GC finalizer of a managed object, which does not depend on
// the template parameter.
V8_EXPORT_PRIVATE void ManagedObjectFinalizer(
const v8::WeakCallbackInfo<void>& data);
// {Managed<T>} is essentially a {std::shared_ptr<T>} allocated on the heap
// that can be used to manage the lifetime of C++ objects that are shared
// across multiple isolates.
// When a {Managed<T>} object is garbage collected (or an isolate which
// contains {Managed<T>} is torn down), the {Managed<T>} deletes its underlying
// {std::shared_ptr<T>}, thereby decrementing its internal reference count,
// which will delete the C++ object when the reference count drops to 0.
template <class CppType>
class Managed : public Foreign {
Managed() : Foreign() {}
explicit Managed(Address ptr) : Foreign(ptr) {}
Managed* operator->() { return this; }
// Get a raw pointer to the C++ object.
V8_INLINE CppType* raw() { return GetSharedPtrPtr()->get(); }
// Get a reference to the shared pointer to the C++ object.
V8_INLINE const std::shared_ptr<CppType>& get() { return *GetSharedPtrPtr(); }
static Managed cast(Object obj) { return Managed(obj.ptr()); }
static Managed unchecked_cast(Object obj) { return bit_cast<Managed>(obj); }
// Allocate a new {CppType} and wrap it in a {Managed<CppType>}.
template <typename... Args>
static Handle<Managed<CppType>> Allocate(Isolate* isolate,
size_t estimated_size,
Args&&... args) {
return FromSharedPtr(
isolate, estimated_size,
// Create a {Managed<CppType>} from an existing raw {CppType*}. The returned
// object will now own the memory pointed to by {CppType}.
static Handle<Managed<CppType>> FromRawPtr(Isolate* isolate,
size_t estimated_size,
CppType* ptr) {
return FromSharedPtr(isolate, estimated_size,
// Create a {Managed<CppType>} from an existing {std::unique_ptr<CppType>}.
// The returned object will now own the memory pointed to by {CppType}, and
// the unique pointer will be released.
static Handle<Managed<CppType>> FromUniquePtr(
Isolate* isolate, size_t estimated_size,
std::unique_ptr<CppType> unique_ptr) {
return FromSharedPtr(isolate, estimated_size, std::move(unique_ptr));
// Create a {Managed<CppType>} from an existing {std::shared_ptr<CppType>}.
static Handle<Managed<CppType>> FromSharedPtr(
Isolate* isolate, size_t estimated_size,
const std::shared_ptr<CppType>& shared_ptr) {
auto destructor = new ManagedPtrDestructor(
estimated_size, new std::shared_ptr<CppType>{shared_ptr}, Destructor);
Handle<Managed<CppType>> handle = Handle<Managed<CppType>>::cast(
Handle<Object> global_handle = isolate->global_handles()->Create(*handle);
destructor->global_handle_location_ = global_handle.location();
GlobalHandles::MakeWeak(destructor->global_handle_location_, destructor,
return handle;
// Internally this {Foreign} object stores a pointer to a new
// std::shared_ptr<CppType>.
std::shared_ptr<CppType>* GetSharedPtrPtr() {
auto destructor =
return reinterpret_cast<std::shared_ptr<CppType>*>(
// Called by either isolate shutdown or the {ManagedObjectFinalizer} in order
// to actually delete the shared pointer and decrement the shared refcount.
static void Destructor(void* ptr) {
auto shared_ptr_ptr = reinterpret_cast<std::shared_ptr<CppType>*>(ptr);
delete shared_ptr_ptr;
} // namespace internal
} // namespace v8