1 files changed, 59 insertions, 0 deletions
diff --git a/gfx/layers/MemoryPressureObserver.h b/gfx/layers/MemoryPressureObserver.h
new file mode 100644
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+++ b/gfx/layers/MemoryPressureObserver.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: sw=2 ts=8 et :
+ */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_LAYERS_MEMORYPRESSUREOBSERVER_H
+#define MOZILLA_LAYERS_MEMORYPRESSUREOBSERVER_H
+
+#include "nsIObserver.h"
+
+namespace mozilla {
+namespace layers {
+
+// A simple memory pressure observer implementation born out of the realization
+// that almost all of our memory pressure observers do exactly the same thing.
+//
+// The intended way to use it is to have the class that nees to react on memory
+// pressure inherit the MemoryPressureListener interface and own a strong
+// reference to a MemoryPressureListener object.
+// Call Unregister on the listener in the destructor of your class or whenever
+// you do not which to receive the notification anymore, otherwise the listener
+// will be held alive by the observer service (leak) and keep a dangling pointer
+// to your class.
+
+/// See nsIMemory.idl
+enum class MemoryPressureReason {
+  LOW_MEMORY,
+  LOW_MEMORY_ONGOING,
+  HEAP_MINIMIZE,
+};
+
+class MemoryPressureListener {
+ public:
+  virtual void OnMemoryPressure(MemoryPressureReason aWhy) = 0;
+};
+
+class MemoryPressureObserver final : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  // Returns null if anything goes wrong.
+  static already_AddRefed<MemoryPressureObserver> Create(
+      MemoryPressureListener* aListener);
+
+  void Unregister();
+
+ private:
+  explicit MemoryPressureObserver(MemoryPressureListener* aListener);
+  virtual ~MemoryPressureObserver();
+  MemoryPressureListener* mListener;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif