allocation.h

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// Copyright 2020 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_ALLOCATION_H_
#define INCLUDE_CPPGC_ALLOCATION_H_
 
#include <stdint.h>
 
#include <atomic>
 
#include "cppgc/custom-space.h"
#include "cppgc/garbage-collected.h"
#include "cppgc/heap.h"
#include "cppgc/internal/api-constants.h"
#include "cppgc/internal/gc-info.h"
 
namespace cppgc {
 
template <typename T>
class MakeGarbageCollectedTraitBase;
 
namespace internal {
 
class V8_EXPORT MakeGarbageCollectedTraitInternal {
 protected:
  static inline void MarkObjectAsFullyConstructed(const void* payload) {
    // See api_constants for an explanation of the constants.
    std::atomic<uint16_t>* atomic_mutable_bitfield =
        reinterpret_cast<std::atomic<uint16_t>*>(
            const_cast<uint16_t*>(reinterpret_cast<const uint16_t*>(
                reinterpret_cast<const uint8_t*>(payload) -
                api_constants::kFullyConstructedBitFieldOffsetFromPayload)));
    uint16_t value = atomic_mutable_bitfield->load(std::memory_order_relaxed);
    value = value | api_constants::kFullyConstructedBitMask;
    atomic_mutable_bitfield->store(value, std::memory_order_release);
  }
 
  static void* Allocate(cppgc::Heap* heap, size_t size, GCInfoIndex index);
  static void* Allocate(cppgc::Heap* heapx, size_t size, GCInfoIndex index,
                        CustomSpaceIndex space_inde);
 
  friend class HeapObjectHeader;
};
 
}  // namespace internal
 
template <typename T>
class MakeGarbageCollectedTraitBase
    : private internal::MakeGarbageCollectedTraitInternal {
 private:
  template <typename U, typename CustomSpace>
  struct SpacePolicy {
    static void* Allocate(Heap* heap, size_t size) {
      // Custom space.
      static_assert(std::is_base_of<CustomSpaceBase, CustomSpace>::value,
                    "Custom space must inherit from CustomSpaceBase.");
      return internal::MakeGarbageCollectedTraitInternal::Allocate(
          heap, size, internal::GCInfoTrait<T>::Index(),
          CustomSpace::kSpaceIndex);
    }
  };
 
  template <typename U>
  struct SpacePolicy<U, void> {
    static void* Allocate(Heap* heap, size_t size) {
      // Default space.
      return internal::MakeGarbageCollectedTraitInternal::Allocate(
          heap, size, internal::GCInfoTrait<T>::Index());
    }
  };
 
 protected:
  static void* Allocate(Heap* heap, size_t size) {
    return SpacePolicy<T, typename SpaceTrait<T>::Space>::Allocate(heap, size);
  }
 
  static void MarkObjectAsFullyConstructed(const void* payload) {
    internal::MakeGarbageCollectedTraitInternal::MarkObjectAsFullyConstructed(
        payload);
  }
};
 
template <typename T>
class MakeGarbageCollectedTrait : public MakeGarbageCollectedTraitBase<T> {
 public:
  template <typename... Args>
  static T* Call(Heap* heap, Args&&... args) {
    static_assert(internal::IsGarbageCollectedType<T>::value,
                  "T needs to be a garbage collected object");
    static_assert(
        !internal::IsGarbageCollectedMixinType<T>::value ||
            sizeof(T) <= internal::api_constants::kLargeObjectSizeThreshold,
        "GarbageCollectedMixin may not be a large object");
    void* memory = MakeGarbageCollectedTraitBase<T>::Allocate(heap, sizeof(T));
    T* object = ::new (memory) T(std::forward<Args>(args)...);
    MakeGarbageCollectedTraitBase<T>::MarkObjectAsFullyConstructed(object);
    return object;
  }
};
 
template <typename T, typename = void>
struct PostConstructionCallbackTrait {
  static void Call(T*) {}
};
 
template <typename T, typename... Args>
T* MakeGarbageCollected(Heap* heap, Args&&... args) {
  T* object =
      MakeGarbageCollectedTrait<T>::Call(heap, std::forward<Args>(args)...);
  PostConstructionCallbackTrait<T>::Call(object);
  return object;
}
 
}  // namespace cppgc
 
#endif  // INCLUDE_CPPGC_ALLOCATION_H_