prefinalizer.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_PREFINALIZER_H_
#define INCLUDE_CPPGC_PREFINALIZER_H_
 
#include "cppgc/internal/compiler-specific.h"
#include "cppgc/liveness-broker.h"
 
namespace cppgc {
 
namespace internal {
 
class V8_EXPORT PrefinalizerRegistration final {
 public:
  using Callback = bool (*)(const cppgc::LivenessBroker&, void*);
 
  PrefinalizerRegistration(void*, Callback);
 
  void* operator new(size_t, void* location) = delete;
  void* operator new(size_t) = delete;
};
 
}  // namespace internal
 
/**
 * Macro must be used in the private section of `Class` and registers a
 * prefinalization callback `void Class::PreFinalizer()`. The callback is
 * invoked on garbage collection after the collector has found an object to be
 * dead.
 *
 * Callback properties:
 * - The callback is invoked before a possible destructor for the corresponding
 *   object.
 * - The callback may access the whole object graph, irrespective of whether
 *   objects are considered dead or alive.
 * - The callback is invoked on the same thread as the object was created on.
 *
 * Example:
 * \code
 * class WithPrefinalizer : public GarbageCollected<WithPrefinalizer> {
 *   CPPGC_USING_PRE_FINALIZER(WithPrefinalizer, Dispose);
 *
 *  public:
 *   void Trace(Visitor*) const {}
 *   void Dispose() { prefinalizer_called = true; }
 *   ~WithPrefinalizer() {
 *     // prefinalizer_called == true
 *   }
 *  private:
 *   bool prefinalizer_called = false;
 * };
 * \endcode
 */
#define CPPGC_USING_PRE_FINALIZER(Class, PreFinalizer)
 public:
  static bool InvokePreFinalizer(const cppgc::LivenessBroker& liveness_broker,
                                 void* object) {
    static_assert(cppgc::IsGarbageCollectedOrMixinTypeV<Class>,
                  "Only garbage collected objects can have prefinalizers");
    Class* self = static_cast<Class*>(object);
    if (liveness_broker.IsHeapObjectAlive(self)) return false;
    self->PreFinalizer();
    return true;
  }
 
 private:
  CPPGC_NO_UNIQUE_ADDRESS cppgc::internal::PrefinalizerRegistration
      prefinalizer_dummy_{this, Class::InvokePreFinalizer};
  static_assert(true, "Force semicolon.")
 
}  // namespace cppgc
 
#endif  // INCLUDE_CPPGC_PREFINALIZER_H_