explicit-management.h

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// 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_CPPGC_EXPLICIT_MANAGEMENT_H_
#define INCLUDE_CPPGC_EXPLICIT_MANAGEMENT_H_
 
#include <cstddef>
#include <limits>
 
#include "cppgc/allocation.h"
#include "cppgc/internal/logging.h"
#include "cppgc/type-traits.h"
 
namespace cppgc {
 
class HeapHandle;
 
namespace subtle {
 
template <typename T>
void FreeUnreferencedObject(HeapHandle& heap_handle, T& object);
template <typename T>
bool Resize(T& object, AdditionalBytes additional_bytes);
 
}  // namespace subtle
 
namespace internal {
 
class ExplicitManagementImpl final {
 private:
  V8_EXPORT static void FreeUnreferencedObject(HeapHandle&, void*);
  V8_EXPORT static bool Resize(void*, size_t);
 
  template <typename T>
  friend void subtle::FreeUnreferencedObject(HeapHandle&, T&);
  template <typename T>
  friend bool subtle::Resize(T&, AdditionalBytes);
};
}  // namespace internal
 
namespace subtle {
 
template <typename T>
void FreeUnreferencedObject(HeapHandle& heap_handle, T& object) {
  static_assert(IsGarbageCollectedTypeV<T>,
                "Object must be of type GarbageCollected.");
  internal::ExplicitManagementImpl::FreeUnreferencedObject(heap_handle,
                                                           &object);
}
 
template <typename T>
bool Resize(T& object, AdditionalBytes additional_bytes) {
  static_assert(IsGarbageCollectedTypeV<T>,
                "Object must be of type GarbageCollected.");
  static_assert(sizeof(T) <= std::numeric_limits<uint32_t>::max());
  const size_t new_object_size = sizeof(T) + additional_bytes.value;
  // On 64-bit systems, since sizeof(T) and additional_bytes.value are both at
  // most 32 bits, we know that their sum can't overflow. On 32-bit systems, we
  // need to check it.
#if !defined(V8_HOST_ARCH_64_BIT)
  if (new_object_size < sizeof(T)) {
    return false;
  }
#endif
  return internal::ExplicitManagementImpl::Resize(&object, new_object_size);
}
 
}  // namespace subtle
}  // namespace cppgc
 
#endif  // INCLUDE_CPPGC_EXPLICIT_MANAGEMENT_H_