third_party/WebKit/Source/platform/MemoryPurgeController.h

// Copyright 2015 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 MemoryPurgeController_h
#define MemoryPurgeController_h

#include "platform/PlatformExport.h"
#include "platform/heap/Handle.h"
#include "wtf/MainThread.h"

namespace blink {

enum class MemoryPurgeMode {
  // The tab contains the webview went to background
  InactiveTab,
  // TODO(bashi): Add more modes as needed.
};

enum class DeviceKind {
  NotSpecified,
  LowEnd,
};

// Classes which have discardable/reducible memory can implement this
// interface to be informed when they should reduce memory consumption.
// MemoryPurgeController assumes that subclasses of MemoryPurgeClient are
// WillBes.
class MemoryPurgeClient : public WillBeGarbageCollectedMixin {
 public:
  virtual ~MemoryPurgeClient() {}

  // MemoryPurgeController invokes this callback when a memory purge event
  // has occurred.
  virtual void purgeMemory(MemoryPurgeMode, DeviceKind) = 0;

  DECLARE_TRACE();
};

// MemoryPurgeController listens to some events which could be opportunities
// for reducing memory consumption and notifies its clients.
// Since we want to control memory per tab, MemoryPurgeController is owned by
// Page.
class PLATFORM_EXPORT MemoryPurgeController final
    : public NoBaseWillBeGarbageCollected<MemoryPurgeController> {
  DECLARE_EMPTY_DESTRUCTOR_WILL_BE_REMOVED(MemoryPurgeController);

 public:
  static PassOwnPtrWillBeRawPtr<MemoryPurgeController> create() {
    return adoptPtrWillBeNoop(new MemoryPurgeController);
  }

  void registerClient(MemoryPurgeClient* client) {
    ASSERT(isMainThread());
    ASSERT(client);
    ASSERT(!m_clients.contains(client));
    m_clients.add(client);
  }

  void unregisterClient(MemoryPurgeClient* client) {
    ASSERT(isMainThread());
    ASSERT(m_clients.contains(client));
    m_clients.remove(client);
  }

  DECLARE_TRACE();

 private:
  MemoryPurgeController();

  void purgeMemory(MemoryPurgeMode);

  WillBeHeapHashSet<RawPtrWillBeWeakMember<MemoryPurgeClient>> m_clients;
  DeviceKind m_deviceKind;
};

}  // namespace blink

#endif  // MemoryPurgeController_h