ef53e0a0d2
The methods in explicit_management.h should be called via the public variants in the subtle namespace. Calling the variants in the internal namespace directly skips asserts and required size coversions. Doing so may cause misuse of the api that may break GC inernals Change-Id: I58a0f324ca1ee0839bb85eb9b53ce57785dc7b91 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3435187 Reviewed-by: Michael Lippautz <mlippautz@chromium.org> Commit-Queue: Omer Katz <omerkatz@chromium.org> Cr-Commit-Position: refs/heads/main@{#78920}
101 lines
3.3 KiB
C++
101 lines
3.3 KiB
C++
// Copyright 2021 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef INCLUDE_CPPGC_EXPLICIT_MANAGEMENT_H_
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#define INCLUDE_CPPGC_EXPLICIT_MANAGEMENT_H_
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#include <cstddef>
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#include "cppgc/allocation.h"
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#include "cppgc/internal/logging.h"
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#include "cppgc/type-traits.h"
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namespace cppgc {
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class HeapHandle;
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namespace subtle {
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template <typename T>
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void FreeUnreferencedObject(HeapHandle& heap_handle, T& object);
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template <typename T>
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bool Resize(T& object, AdditionalBytes additional_bytes);
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} // namespace subtle
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namespace internal {
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class ExplicitManagementImpl final {
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private:
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V8_EXPORT static void FreeUnreferencedObject(HeapHandle&, void*);
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V8_EXPORT static bool Resize(void*, size_t);
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template <typename T>
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friend void subtle::FreeUnreferencedObject(HeapHandle&, T&);
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template <typename T>
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friend bool subtle::Resize(T&, AdditionalBytes);
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};
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} // namespace internal
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namespace subtle {
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/**
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* Informs the garbage collector that `object` can be immediately reclaimed. The
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* destructor may not be invoked immediately but only on next garbage
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* collection.
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*
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* It is up to the embedder to guarantee that no other object holds a reference
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* to `object` after calling `FreeUnreferencedObject()`. In case such a
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* reference exists, it's use results in a use-after-free.
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*
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* To aid in using the API, `FreeUnreferencedObject()` may be called from
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* destructors on objects that would be reclaimed in the same garbage collection
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* cycle.
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*
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* \param heap_handle The corresponding heap.
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* \param object Reference to an object that is of type `GarbageCollected` and
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* should be immediately reclaimed.
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*/
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template <typename T>
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void FreeUnreferencedObject(HeapHandle& heap_handle, T& object) {
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static_assert(IsGarbageCollectedTypeV<T>,
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"Object must be of type GarbageCollected.");
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internal::ExplicitManagementImpl::FreeUnreferencedObject(heap_handle,
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&object);
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}
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/**
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* Tries to resize `object` of type `T` with additional bytes on top of
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* sizeof(T). Resizing is only useful with trailing inlined storage, see e.g.
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* `MakeGarbageCollected(AllocationHandle&, AdditionalBytes)`.
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*
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* `Resize()` performs growing or shrinking as needed and may skip the operation
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* for internal reasons, see return value.
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*
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* It is up to the embedder to guarantee that in case of shrinking a larger
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* object down, the reclaimed area is not used anymore. Any subsequent use
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* results in a use-after-free.
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*
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* The `object` must be live when calling `Resize()`.
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*
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* \param object Reference to an object that is of type `GarbageCollected` and
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* should be resized.
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* \param additional_bytes Bytes in addition to sizeof(T) that the object should
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* provide.
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* \returns true when the operation was successful and the result can be relied
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* on, and false otherwise.
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*/
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template <typename T>
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bool Resize(T& object, AdditionalBytes additional_bytes) {
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static_assert(IsGarbageCollectedTypeV<T>,
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"Object must be of type GarbageCollected.");
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return internal::ExplicitManagementImpl::Resize(
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&object, sizeof(T) + additional_bytes.value);
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}
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} // namespace subtle
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} // namespace cppgc
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#endif // INCLUDE_CPPGC_EXPLICIT_MANAGEMENT_H_
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