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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_VISITOR_H_ #define INCLUDE_CPPGC_VISITOR_H_ #include "cppgc/garbage-collected.h" #include "cppgc/internal/logging.h" #include "cppgc/internal/pointer-policies.h" #include "cppgc/liveness-broker.h" #include "cppgc/member.h" #include "cppgc/source-location.h" #include "cppgc/trace-trait.h" namespace cppgc { namespace internal { class VisitorBase; } // namespace internal using WeakCallback = void (*)(const LivenessBroker&, const void*); /** * Visitor passed to trace methods. All managed pointers must have called the * visitor's trace method on them. */ class Visitor { public: template <typename T> void Trace(const Member<T>& member) { const T* value = member.GetRawAtomic(); CPPGC_DCHECK(value != kSentinelPointer); Trace(value); } template <typename T> void Trace(const WeakMember<T>& weak_member) { static_assert(sizeof(T), "T must be fully defined"); static_assert(internal::IsGarbageCollectedType<T>::value, "T must be GarabgeCollected or GarbageCollectedMixin type"); const T* value = weak_member.GetRawAtomic(); // Bailout assumes that WeakMember emits write barrier. if (!value) { return; } // TODO(chromium:1056170): DCHECK (or similar) for deleted values as they // should come in at a different path. VisitWeak(value, TraceTrait<T>::GetTraceDescriptor(value), &HandleWeak<WeakMember<T>>, &weak_member); } template <typename Persistent, std::enable_if_t<Persistent::IsStrongPersistent::value>* = nullptr> void TraceRoot(const Persistent& p, const SourceLocation& loc) { using PointeeType = typename Persistent::PointeeType; static_assert(sizeof(PointeeType), "Persistent's pointee type must be fully defined"); static_assert(internal::IsGarbageCollectedType<PointeeType>::value, "Persisent's pointee type must be GarabgeCollected or " "GarbageCollectedMixin"); if (!p.Get()) { return; } VisitRoot(p.Get(), TraceTrait<PointeeType>::GetTraceDescriptor(p.Get())); } template < typename WeakPersistent, std::enable_if_t<!WeakPersistent::IsStrongPersistent::value>* = nullptr> void TraceRoot(const WeakPersistent& p, const SourceLocation& loc) { using PointeeType = typename WeakPersistent::PointeeType; static_assert(sizeof(PointeeType), "Persistent's pointee type must be fully defined"); static_assert(internal::IsGarbageCollectedType<PointeeType>::value, "Persisent's pointee type must be GarabgeCollected or " "GarbageCollectedMixin"); VisitWeakRoot(p.Get(), TraceTrait<PointeeType>::GetTraceDescriptor(p.Get()), &HandleWeak<WeakPersistent>, &p); } template <typename T, void (T::*method)(const LivenessBroker&)> void RegisterWeakCallbackMethod(const T* obj) { RegisterWeakCallback(&WeakCallbackMethodDelegate<T, method>, obj); } virtual void RegisterWeakCallback(WeakCallback, const void*) {} protected: virtual void Visit(const void* self, TraceDescriptor) {} virtual void VisitWeak(const void* self, TraceDescriptor, WeakCallback, const void* weak_member) {} virtual void VisitRoot(const void*, TraceDescriptor) {} virtual void VisitWeakRoot(const void* self, TraceDescriptor, WeakCallback, const void* weak_root) {} private: template <typename T, void (T::*method)(const LivenessBroker&)> static void WeakCallbackMethodDelegate(const LivenessBroker& info, const void* self) { // Callback is registered through a potential const Trace method but needs // to be able to modify fields. See HandleWeak. (const_cast<T*>(static_cast<const T*>(self))->*method)(info); } template <typename PointerType> static void HandleWeak(const LivenessBroker& info, const void* object) { const PointerType* weak = static_cast<const PointerType*>(object); const auto* raw = weak->Get(); if (raw && !info.IsHeapObjectAlive(raw)) { // Object is passed down through the marker as const. Alternatives are // - non-const Trace method; // - mutable pointer in MemberBase; const_cast<PointerType*>(weak)->Clear(); } } Visitor() = default; template <typename T> void Trace(const T* t) { static_assert(sizeof(T), "T must be fully defined"); static_assert(internal::IsGarbageCollectedType<T>::value, "T must be GarabgeCollected or GarbageCollectedMixin type"); if (!t) { return; } Visit(t, TraceTrait<T>::GetTraceDescriptor(t)); } friend class internal::VisitorBase; }; } // namespace cppgc #endif // INCLUDE_CPPGC_VISITOR_H_