Adding Baseframework of the ResourceManager (all hooks and observers) are being put in place with a…

athena/resource_manager/memory_pressure_notifier.h

+// Copyright (c) 2014 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 ATHENA_RESOURCE_MANAGER_MEMORY_PRESSURE_NOTIFIER_H_
+#define ATHENA_RESOURCE_MANAGER_MEMORY_PRESSURE_NOTIFIER_H_
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/timer/timer.h"
+
+namespace athena {
+
+class MemoryPressureNotifierImpl;
+class ResourceManagerDelegate;
+
+////////////////////////////////////////////////////////////////////////////////
+// MemoryPressureObserver
+//
+// This observer gets informed once about a |MEMORY_PRESSURE_LOW|. When the
+// pressure exceeds, the observer will get polled until |MEMORY_PRESSURE_LOW| is
+// reached again to counter memory consumption.
+class MemoryPressureObserver {
+ public:
+  MemoryPressureObserver() {}
+  virtual ~MemoryPressureObserver() {}
+
+  // The reported memory pressure. Note: The value is intentionally abstracted
+  // since the real amount of free memory is only estimated (due to e.g. zram).
+  enum MemoryPressure {
+    MEMORY_PRESSURE_UNKNOWN,   // The memory pressure cannot be determined.
+    MEMORY_PRESSURE_LOW,       // Single call if memory fill level is below 50%.
+    MEMORY_PRESSURE_MODERATE,  // Polled for memory fill level of ~50 .. 75%.
+    MEMORY_PRESSURE_HIGH,      // Polled for memory fill level of ~75% .. 90%.
+    MEMORY_PRESSURE_CRITICAL,  // Polled for memory fill level of above ~90%.
+  };
+  // The observer.
+  virtual void OnMemoryPressure(MemoryPressure pressure) = 0;
+
+  // OS system interface functions. The delegate remains owned by the Observer.
+  virtual ResourceManagerDelegate* GetDelegate() = 0;
+};
+
+
+////////////////////////////////////////////////////////////////////////////////
+// MemoryPressureNotifier
+//
+// Class to handle the observation of our free memory. It notifies the owner of
+// memory fill level changes, so that it can take action to reduce memory by
+// reducing active activities.
+//
+// The observer will use 3 different fill levels: 50% full, 75% full and 90%
+// full.
+class MemoryPressureNotifier {
+ public:
+  // The creator gets the |listener| object. Note that the ownership of the
+  // listener object remains with the creator.
+  explicit MemoryPressureNotifier(MemoryPressureObserver* listener);
+  ~MemoryPressureNotifier();
+
+  // Stop observing the memory fill level.
+  // May be safely called if StartObserving has not been called.
+  void StopObserving();
+
+ private:
+  // Starts observing the memory fill level.
+  // Calls to StartObserving should always be matched with calls to
+  // StopObserving.
+  void StartObserving();
+
+  // The function which gets periodically be called to check any changes in the
+  // memory pressure.
+  void CheckMemoryPressure();
+
+  // Converts free percent of memory into a memory pressure value.
+  MemoryPressureObserver::MemoryPressure GetMemoryPressureLevelFromFillLevel(
+      int memory_fill_level);
+
+  base::RepeatingTimer<MemoryPressureNotifier> timer_;
+
+  // The listener which needs to be informed about memory pressure.
+  MemoryPressureObserver* listener_;
+
+  // Our current memory pressure.
+  MemoryPressureObserver::MemoryPressure current_pressure_;
+
+  DISALLOW_COPY_AND_ASSIGN(MemoryPressureNotifier);
+};
+
+}  // namespace athena
+
+#endif  // ATHENA_RESOURCE_MANAGER_MEMORY_PRESSURE_NOTIFIER_H_