gfx/layers/MemoryPressureObserver.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: sw=2 ts=8 et :
   3  */
   4 /* This Source Code Form is subject to the terms of the Mozilla Public
   5  * License, v. 2.0. If a copy of the MPL was not distributed with this
   6  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   7
   8 #ifndef MOZILLA_LAYERS_MEMORYPRESSUREOBSERVER_H
   9 #define MOZILLA_LAYERS_MEMORYPRESSUREOBSERVER_H
  10
  11 #include "nsIObserver.h"
  12
  13 namespace mozilla {
  14 namespace layers {
  15
  16 // A simple memory pressure observer implementation born out of the realization
  17 // that almost all of our memory pressure observers do exactly the same thing.
  18 //
  19 // The intended way to use it is to have the class that nees to react on memory
  20 // pressure inherit the MemoryPressureListener interface and own a strong
  21 // reference to a MemoryPressureListener object.
  22 // Call Unregister on the listener in the destructor of your class or whenever
  23 // you do not which to receive the notification anymore, otherwise the listener
  24 // will be held alive by the observer service (leak) and keep a dangling pointer
  25 // to your class.
  26
  27 /// See nsIMemory.idl
  28 enum class MemoryPressureReason {
  29   LOW_MEMORY,
  30   LOW_MEMORY_ONGOING,
  31   HEAP_MINIMIZE,
  32 };
  33
  34 class MemoryPressureListener {
  35  public:
  36   virtual void OnMemoryPressure(MemoryPressureReason aWhy) = 0;
  37 };
  38
  39 class MemoryPressureObserver final : public nsIObserver {
  40  public:
  41   NS_DECL_ISUPPORTS
  42   NS_DECL_NSIOBSERVER
  43
  44   // Returns null if anything goes wrong.
  45   static already_AddRefed<MemoryPressureObserver> Create(
  46       MemoryPressureListener* aListener);
  47
  48   void Unregister();
  49
  50  private:
  51   explicit MemoryPressureObserver(MemoryPressureListener* aListener);
  52   virtual ~MemoryPressureObserver();
  53   MemoryPressureListener* mListener;
  54 };
  55
  56 }  // namespace layers
  57 }  // namespace mozilla
  58
  59 #endif