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1 // Copyright (c) 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef ATHENA_RESOURCE_MANAGER_MEMORY_PRESSURE_NOTIFIER_H_
6 #define ATHENA_RESOURCE_MANAGER_MEMORY_PRESSURE_NOTIFIER_H_
7 
8 #include "athena/athena_export.h"
9 #include "base/memory/ref_counted.h"
10 #include "base/memory/scoped_ptr.h"
11 #include "base/timer/timer.h"
12 
13 namespace athena {
14 
15 class MemoryPressureNotifierImpl;
16 class ResourceManagerDelegate;
17 
18 ////////////////////////////////////////////////////////////////////////////////
19 // MemoryPressureObserver
20 //
21 // This observer gets informed once about a |MEMORY_PRESSURE_LOW|. When the
22 // pressure exceeds, the observer will get polled until |MEMORY_PRESSURE_LOW| is
23 // reached again to counter memory consumption.
24 class MemoryPressureObserver {
25  public:
MemoryPressureObserver()26   MemoryPressureObserver() {}
~MemoryPressureObserver()27   virtual ~MemoryPressureObserver() {}
28 
29   // The reported memory pressure. Note: The value is intentionally abstracted
30   // since the real amount of free memory is only estimated (due to e.g. zram).
31   // Note: The bigger the index of the pressure level, the more resources are
32   // in use.
33   enum MemoryPressure {
34     MEMORY_PRESSURE_UNKNOWN = 0,   // The memory pressure cannot be determined.
35     MEMORY_PRESSURE_LOW,           // Single call if fill level is below 50%.
36     MEMORY_PRESSURE_MODERATE,      // Polled for fill level of ~50 .. 75%.
37     MEMORY_PRESSURE_HIGH,          // Polled for fill level of ~75% .. 90%.
38     MEMORY_PRESSURE_CRITICAL,      // Polled for fill level of above ~90%.
39   };
40   // The observer.
41   virtual void OnMemoryPressure(MemoryPressure pressure) = 0;
42 
43   // OS system interface functions. The delegate remains owned by the Observer.
44   virtual ResourceManagerDelegate* GetDelegate() = 0;
45 };
46 
47 
48 ////////////////////////////////////////////////////////////////////////////////
49 // MemoryPressureNotifier
50 //
51 // Class to handle the observation of our free memory. It notifies the owner of
52 // memory fill level changes, so that it can take action to reduce memory by
53 // reducing active activities.
54 //
55 // The observer will use 3 different fill levels: 50% full, 75% full and 90%
56 // full.
57 class ATHENA_EXPORT MemoryPressureNotifier {
58  public:
59   // The creator gets the |listener| object. Note that the ownership of the
60   // listener object remains with the creator.
61   explicit MemoryPressureNotifier(MemoryPressureObserver* listener);
62   ~MemoryPressureNotifier();
63 
64   // Stop observing the memory fill level.
65   // May be safely called if StartObserving has not been called.
66   void StopObserving();
67 
68  private:
69   // Starts observing the memory fill level.
70   // Calls to StartObserving should always be matched with calls to
71   // StopObserving.
72   void StartObserving();
73 
74   // The function which gets periodically be called to check any changes in the
75   // memory pressure.
76   void CheckMemoryPressure();
77 
78   // Converts free percent of memory into a memory pressure value.
79   MemoryPressureObserver::MemoryPressure GetMemoryPressureLevelFromFillLevel(
80       int memory_fill_level);
81 
82   base::RepeatingTimer<MemoryPressureNotifier> timer_;
83 
84   // The listener which needs to be informed about memory pressure.
85   MemoryPressureObserver* listener_;
86 
87   // Our current memory pressure.
88   MemoryPressureObserver::MemoryPressure current_pressure_;
89 
90   DISALLOW_COPY_AND_ASSIGN(MemoryPressureNotifier);
91 };
92 
93 }  // namespace athena
94 
95 #endif  // ATHENA_RESOURCE_MANAGER_MEMORY_PRESSURE_NOTIFIER_H_
96