third_party/blink/renderer/platform/heap/trace_traits.h

// Copyright 2021 The Chromium 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 THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_TRACE_TRAITS_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_TRACE_TRAITS_H_

#include "third_party/blink/renderer/platform/heap/heap.h"
#include "third_party/blink/renderer/platform/heap/member.h"
#include "third_party/blink/renderer/platform/heap/visitor.h"
#include "third_party/blink/renderer/platform/wtf/buildflags.h"
#include "third_party/blink/renderer/platform/wtf/hash_table.h"

#if BUILDFLAG(USE_V8_OILPAN)
#include "third_party/blink/renderer/platform/heap/v8_wrapper/trace_traits.h"
#else  // !USE_V8_OILPAN
#include "third_party/blink/renderer/platform/heap/impl/trace_traits.h"
#endif  // !USE_V8_OILPAN

namespace WTF {

// Catch-all for types that have a way to trace that don't have special
// handling for weakness in collections.  This means that if this type
// contains WeakMember fields, they will simply be zeroed, but the entry
// will not be removed from the collection.  This always happens for
// things in vectors, which don't currently support special handling of
// weak elements.
template <typename T, typename Traits>
struct TraceInCollectionTrait<kNoWeakHandling, T, Traits> {
  static bool IsAlive(const blink::LivenessBroker& info, const T& t) {
    return true;
  }

  static void Trace(blink::Visitor* visitor, const T& t) {
    static_assert(IsTraceableInCollectionTrait<Traits>::value,
                  "T should be traceable");
    visitor->Trace(t);
  }
};

template <typename T, typename Traits>
struct TraceInCollectionTrait<kNoWeakHandling, blink::WeakMember<T>, Traits> {
  static void Trace(blink::Visitor* visitor, const blink::WeakMember<T>& t) {
    // Extract raw pointer to avoid using the WeakMember<> overload in Visitor.
    visitor->TraceStrongly(t);
  }
};

// Catch-all for types that have HashTrait support for tracing with weakness.
// Empty to enforce specialization.
template <typename T, typename Traits>
struct TraceInCollectionTrait<kWeakHandling, T, Traits> {};

template <typename T, typename Traits>
struct TraceInCollectionTrait<kWeakHandling, blink::WeakMember<T>, Traits> {
  static bool IsAlive(const blink::LivenessBroker& info,
                      const blink::WeakMember<T>& value) {
    return info.IsHeapObjectAlive(value);
  }
};

}  // namespace WTF

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_TRACE_TRAITS_H_