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1 : // Copyright 2016 the V8 project authors. All rights reserved.
2 : // Use of this source code is governed by a BSD-style license that can be
3 : // found in the LICENSE file.
4 :
5 : #ifndef V8_OBJECTS_MANAGED_H_
6 : #define V8_OBJECTS_MANAGED_H_
7 :
8 : #include <memory>
9 : #include "src/global-handles.h"
10 : #include "src/handles.h"
11 : #include "src/heap/factory.h"
12 : #include "src/isolate.h"
13 : #include "src/objects/foreign.h"
14 :
15 : namespace v8 {
16 : namespace internal {
17 :
18 : // Implements a doubly-linked lists of destructors for the isolate.
19 : struct ManagedPtrDestructor {
20 : // Estimated size of external memory associated with the managed object.
21 : // This is used to adjust the garbage collector's heuristics upon
22 : // allocation and deallocation of a managed object.
23 : size_t estimated_size_ = 0;
24 : ManagedPtrDestructor* prev_ = nullptr;
25 : ManagedPtrDestructor* next_ = nullptr;
26 : void* shared_ptr_ptr_ = nullptr;
27 : void (*destructor_)(void* shared_ptr) = nullptr;
28 : Address* global_handle_location_ = nullptr;
29 :
30 : ManagedPtrDestructor(size_t estimated_size, void* shared_ptr_ptr,
31 : void (*destructor)(void*))
32 : : estimated_size_(estimated_size),
33 : shared_ptr_ptr_(shared_ptr_ptr),
34 3118267 : destructor_(destructor) {}
35 : };
36 :
37 : // The GC finalizer of a managed object, which does not depend on
38 : // the template parameter.
39 : V8_EXPORT_PRIVATE void ManagedObjectFinalizer(
40 : const v8::WeakCallbackInfo<void>& data);
41 :
42 : // {Managed<T>} is essentially a {std::shared_ptr<T>} allocated on the heap
43 : // that can be used to manage the lifetime of C++ objects that are shared
44 : // across multiple isolates.
45 : // When a {Managed<T>} object is garbage collected (or an isolate which
46 : // contains {Managed<T>} is torn down), the {Managed<T>} deletes its underlying
47 : // {std::shared_ptr<T>}, thereby decrementing its internal reference count,
48 : // which will delete the C++ object when the reference count drops to 0.
49 : template <class CppType>
50 : class Managed : public Foreign {
51 : public:
52 12866688 : Managed() : Foreign() {}
53 : explicit Managed(Address ptr) : Foreign(ptr) {}
54 : Managed* operator->() { return this; }
55 :
56 : // Get a raw pointer to the C++ object.
57 11818887 : V8_INLINE CppType* raw() { return GetSharedPtrPtr()->get(); }
58 :
59 : // Get a reference to the shared pointer to the C++ object.
60 157202 : V8_INLINE const std::shared_ptr<CppType>& get() { return *GetSharedPtrPtr(); }
61 :
62 : static Managed cast(Object obj) { return Managed(obj->ptr()); }
63 5365016 : static Managed unchecked_cast(Object obj) { return bit_cast<Managed>(obj); }
64 :
65 : // Allocate a new {CppType} and wrap it in a {Managed<CppType>}.
66 : template <typename... Args>
67 1752630 : static Handle<Managed<CppType>> Allocate(Isolate* isolate,
68 : size_t estimated_size,
69 : Args&&... args) {
70 1752630 : return FromSharedPtr(
71 : isolate, estimated_size,
72 3505259 : std::make_shared<CppType>(std::forward<Args>(args)...));
73 : }
74 :
75 : // Create a {Managed<CppType>} from an existing raw {CppType*}. The returned
76 : // object will now own the memory pointed to by {CppType}.
77 113851 : static Handle<Managed<CppType>> FromRawPtr(Isolate* isolate,
78 : size_t estimated_size,
79 : CppType* ptr) {
80 113851 : return FromSharedPtr(isolate, estimated_size,
81 227702 : std::shared_ptr<CppType>{ptr});
82 : }
83 :
84 : // Create a {Managed<CppType>} from an existing {std::unique_ptr<CppType>}.
85 : // The returned object will now own the memory pointed to by {CppType}, and
86 : // the unique pointer will be released.
87 12666 : static Handle<Managed<CppType>> FromUniquePtr(
88 : Isolate* isolate, size_t estimated_size,
89 : std::unique_ptr<CppType> unique_ptr) {
90 25332 : return FromSharedPtr(isolate, estimated_size, std::move(unique_ptr));
91 : }
92 :
93 : // Create a {Managed<CppType>} from an existing {std::shared_ptr<CppType>}.
94 3118261 : static Handle<Managed<CppType>> FromSharedPtr(
95 : Isolate* isolate, size_t estimated_size,
96 : const std::shared_ptr<CppType>& shared_ptr) {
97 : reinterpret_cast<v8::Isolate*>(isolate)
98 3118261 : ->AdjustAmountOfExternalAllocatedMemory(estimated_size);
99 : auto destructor = new ManagedPtrDestructor(
100 6236524 : estimated_size, new std::shared_ptr<CppType>{shared_ptr}, Destructor);
101 3118262 : Handle<Managed<CppType>> handle = Handle<Managed<CppType>>::cast(
102 : isolate->factory()->NewForeign(reinterpret_cast<Address>(destructor)));
103 : Handle<Object> global_handle = isolate->global_handles()->Create(*handle);
104 3118262 : destructor->global_handle_location_ = global_handle.location();
105 3118262 : GlobalHandles::MakeWeak(destructor->global_handle_location_, destructor,
106 : &ManagedObjectFinalizer,
107 : v8::WeakCallbackType::kParameter);
108 3118262 : isolate->RegisterManagedPtrDestructor(destructor);
109 3118261 : return handle;
110 : }
111 :
112 : private:
113 : // Internally this {Foreign} object stores a pointer to a new
114 : // std::shared_ptr<CppType>.
115 11976088 : std::shared_ptr<CppType>* GetSharedPtrPtr() {
116 : auto destructor =
117 12645417 : reinterpret_cast<ManagedPtrDestructor*>(foreign_address());
118 : return reinterpret_cast<std::shared_ptr<CppType>*>(
119 12645417 : destructor->shared_ptr_ptr_);
120 : }
121 :
122 : // Called by either isolate shutdown or the {ManagedObjectFinalizer} in order
123 : // to actually delete the shared pointer and decrement the shared refcount.
124 3118262 : static void Destructor(void* ptr) {
125 : auto shared_ptr_ptr = reinterpret_cast<std::shared_ptr<CppType>*>(ptr);
126 6236524 : delete shared_ptr_ptr;
127 3118262 : }
128 : };
129 :
130 : } // namespace internal
131 : } // namespace v8
132 :
133 : #endif // V8_OBJECTS_MANAGED_H_
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