garbage-collected.h

Go to the documentation of this file.

// 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_GARBAGE_COLLECTED_H_
#define INCLUDE_CPPGC_GARBAGE_COLLECTED_H_
 
#include <type_traits>
 
#include "cppgc/internal/api-constants.h"
#include "cppgc/platform.h"
#include "cppgc/trace-trait.h"
#include "cppgc/type-traits.h"
 
namespace cppgc {
 
class Visitor;
 
namespace internal {
 
class GarbageCollectedBase {
 public:
  // Must use MakeGarbageCollected.
  void* operator new(size_t) = delete;
  void* operator new[](size_t) = delete;
  // The garbage collector is taking care of reclaiming the object. Also,
  // virtual destructor requires an unambiguous, accessible 'operator delete'.
  void operator delete(void*) {
#ifdef V8_ENABLE_CHECKS
    internal::Abort();
#endif  // V8_ENABLE_CHECKS
  }
  void operator delete[](void*) = delete;
 
 protected:
  GarbageCollectedBase() = default;
};
 
}  // namespace internal
 
template <typename>
class GarbageCollected : public internal::GarbageCollectedBase {
 public:
  using IsGarbageCollectedTypeMarker = void;
 
 protected:
  GarbageCollected() = default;
};
 
class GarbageCollectedMixin : public internal::GarbageCollectedBase {
 public:
  using IsGarbageCollectedMixinTypeMarker = void;
 
  // Sentinel used to mark not-fully-constructed mixins.
  static constexpr void* kNotFullyConstructedObject = nullptr;
 
  // Provide default implementation that indicate that the vtable is not yet
  // set up properly. This is used to to get GCInfo objects for mixins so that
  // these objects can be processed later on.
  virtual TraceDescriptor GetTraceDescriptor() const {
    return {kNotFullyConstructedObject, nullptr};
  }
 
  virtual void Trace(cppgc::Visitor*) const {}
};
 
#define USING_GARBAGE_COLLECTED_MIXIN()                                      \
 public:                                                                     \
  /* Marker is used by clang to check for proper usages of the macro. */     \
  typedef int HasUsingGarbageCollectedMixinMacro;                            \
                                                                             \
  TraceDescriptor GetTraceDescriptor() const override {                      \
    static_assert(                                                           \
        internal::IsSubclassOfTemplate<                                      \
            std::remove_const_t<std::remove_pointer_t<decltype(this)>>,      \
            cppgc::GarbageCollected>::value,                                 \
        "Only garbage collected objects can have garbage collected mixins"); \
    return {this, TraceTrait<std::remove_const_t<                            \
                      std::remove_pointer_t<decltype(this)>>>::Trace};       \
  }                                                                          \
                                                                             \
 private:                                                                    \
  static_assert(true, "Force semicolon.")
 
#define MERGE_GARBAGE_COLLECTED_MIXINS()                \
 public:                                                \
  /* When using multiple mixins the methods become  */  \
  /* ambigous. Providing additional implementations */  \
  /* disambiguate them again.                       */  \
  TraceDescriptor GetTraceDescriptor() const override { \
    return {kNotFullyConstructedObject, nullptr};       \
  }                                                     \
                                                        \
 private:                                               \
  static_assert(true, "Force semicolon.")
 
}  // namespace cppgc
 
#endif  // INCLUDE_CPPGC_GARBAGE_COLLECTED_H_