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

// Copyright 2018 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_UNIFIED_HEAP_CONTROLLER_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_UNIFIED_HEAP_CONTROLLER_H_

#include "base/macros.h"
#include "third_party/blink/renderer/platform/platform_export.h"
#include "v8/include/v8.h"

namespace blink {

class ThreadState;

// UnifiedHeapController ties V8's garbage collector to Oilpan for performing a
// garbage collection across both managed heaps.
//
// Unified heap garbage collections are triggered by V8 and mark the full
// transitive closure of V8 and Blink (Oilpan) objects. The garbage collection
// is initially triggered by V8. Both collecters report live references using
// the EmbedderHeapTracer APIs. V8 and Blink both run separate incremental
// marking steps to compute their live closures, respectively. The final atomic
// pause is then initiated by V8 and triggers a fixed-point computation between
// V8 and Blink where both GCs report live references to each other and drain
// their marking work lists until they are empty and no new references are
// found.
//
// Oilpan does not consider references from DOM wrappers (JavaScript objects on
// V8's heap) as roots for such garbage collections.
class PLATFORM_EXPORT UnifiedHeapController final
    : public v8::EmbedderHeapTracer {
  DISALLOW_IMPLICIT_CONSTRUCTORS(UnifiedHeapController);

 public:
  explicit UnifiedHeapController(ThreadState*);

  // v8::EmbedderHeapTracer implementation.
  void TracePrologue() final;
  void TraceEpilogue() final;
  void EnterFinalPause(EmbedderStackState) final;
  void RegisterV8References(const std::vector<std::pair<void*, void*>>&) final;
  bool AdvanceTracing(double) final;
  bool IsTracingDone() final;

  ThreadState* thread_state() const { return thread_state_; }

 private:
  ThreadState* const thread_state_;

  // Returns whether the Blink heap has been fully processed.
  bool is_tracing_done_ = false;
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_UNIFIED_HEAP_CONTROLLER_H_