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1// Copyright 2020 the V8 project authors. All rights reserved.2// Use of this source code is governed by a BSD-style license that can be3// found in the LICENSE file.4 5#ifndef INCLUDE_CPPGC_TRACE_TRAIT_H_6#define INCLUDE_CPPGC_TRACE_TRAIT_H_7 8#include <type_traits>9 10#include "cppgc/type-traits.h"11#include "v8config.h"  // NOLINT(build/include_directory)12 13namespace cppgc {14 15class Visitor;16 17namespace internal {18 19class RootVisitor;20 21using TraceRootCallback = void (*)(RootVisitor&, const void* object);22 23// Implementation of the default TraceTrait handling GarbageCollected and24// GarbageCollectedMixin.25template <typename T,26          bool =27              IsGarbageCollectedMixinTypeV<typename std::remove_const<T>::type>>28struct TraceTraitImpl;29 30}  // namespace internal31 32/**33 * Callback for invoking tracing on a given object.34 *35 * \param visitor The visitor to dispatch to.36 * \param object The object to invoke tracing on.37 */38using TraceCallback = void (*)(Visitor* visitor, const void* object);39 40/**41 * Describes how to trace an object, i.e., how to visit all Oilpan-relevant42 * fields of an object.43 */44struct TraceDescriptor {45  /**46   * Adjusted base pointer, i.e., the pointer to the class inheriting directly47   * from GarbageCollected, of the object that is being traced.48   */49  const void* base_object_payload;50  /**51   * Callback for tracing the object.52   */53  TraceCallback callback;54};55 56/**57 * Callback for getting a TraceDescriptor for a given address.58 *59 * \param address Possibly inner address of an object.60 * \returns a TraceDescriptor for the provided address.61 */62using TraceDescriptorCallback = TraceDescriptor (*)(const void* address);63 64namespace internal {65 66struct V8_EXPORT TraceTraitFromInnerAddressImpl {67  static TraceDescriptor GetTraceDescriptor(const void* address);68};69 70/**71 * Trait specifying how the garbage collector processes an object of type T.72 *73 * Advanced users may override handling by creating a specialization for their74 * type.75 */76template <typename T>77struct TraceTraitBase {78  static_assert(internal::IsTraceableV<T>, "T must have a Trace() method");79 80  /**81   * Accessor for retrieving a TraceDescriptor to process an object of type T.82   *83   * \param self The object to be processed.84   * \returns a TraceDescriptor to process the object.85   */86  static TraceDescriptor GetTraceDescriptor(const void* self) {87    return internal::TraceTraitImpl<T>::GetTraceDescriptor(88        static_cast<const T*>(self));89  }90 91  /**92   * Function invoking the tracing for an object of type T.93   *94   * \param visitor The visitor to dispatch to.95   * \param self The object to invoke tracing on.96   */97  static void Trace(Visitor* visitor, const void* self) {98    static_cast<const T*>(self)->Trace(visitor);99  }100};101 102}  // namespace internal103 104template <typename T>105struct TraceTrait : public internal::TraceTraitBase<T> {};106 107namespace internal {108 109template <typename T>110struct TraceTraitImpl<T, false> {111  static_assert(IsGarbageCollectedTypeV<T>,112                "T must be of type GarbageCollected or GarbageCollectedMixin");113  static TraceDescriptor GetTraceDescriptor(const void* self) {114    return {self, TraceTrait<T>::Trace};115  }116};117 118template <typename T>119struct TraceTraitImpl<T, true> {120  static TraceDescriptor GetTraceDescriptor(const void* self) {121    return internal::TraceTraitFromInnerAddressImpl::GetTraceDescriptor(self);122  }123};124 125}  // namespace internal126}  // namespace cppgc127 128#endif  // INCLUDE_CPPGC_TRACE_TRAIT_H_129