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v8/include/cppgc/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_