Created multi-process-friendly PowerMonitor interface.

base/power_monitor/power_monitor_source.h

Index: base/power_monitor/power_monitor_source.h
diff --git a/base/power_monitor/power_monitor_source.h b/base/power_monitor/power_monitor_source.h
new file mode 100644
index 0000000000000000000000000000000000000000..0fb3f146c3424f3933b53e154c8425e91223c826
--- /dev/null
+++ b/base/power_monitor/power_monitor_source.h
@@ -0,0 +1,63 @@
+// Copyright 2013 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 BASE_POWER_MONITOR_POWER_MONITOR_SOURCE_H_
+#define BASE_POWER_MONITOR_POWER_MONITOR_SOURCE_H_
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/observer_list_threadsafe.h"
+#include "base/synchronization/lock.h"
+
+namespace base {
+
+class PowerMonitor;
+
+// Communicates power state changes to the power monitor.
+class BASE_EXPORT PowerMonitorSource {
+ public:
+  PowerMonitorSource();
+  virtual ~PowerMonitorSource();
+
+  // Normalized list of power events.
+  enum PowerEvent {
+    POWER_STATE_EVENT,  // The Power status of the system has changed.
+    SUSPEND_EVENT,      // The system is being suspended.
+    RESUME_EVENT        // The system is being resumed.
+  };
+
+  // Is the computer currently on battery power. Can be called on any thread.
+  bool IsOnBatteryPower();
+
+ protected:
+  friend class PowerMonitorTest;
+
+  // Friend function that is allowed to access the protected ProcessPowerEvent.
+  friend void ProcessPowerEventHelper(PowerEvent);
+
+  // Get the process-wide PowerMonitorSource (if not present, returns NULL).
+  static PowerMonitorSource* Get();
+
+  static void ProcessPowerEvent(PowerEvent event_id);
+
+  // Updates the cached battery power state. Returns true if state has changed.
+  bool UpdateOnBatteryPower();
+
+  // Platform-specific method to check whether the system is currently
+  // running on battery power.  Returns true if running on batteries,
+  // false otherwise.
+  virtual bool IsOnBatteryPowerImpl() = 0;
+
+ private:
+  bool on_battery_power_;
+  bool suspended_;
+  Lock lock_;

[piman, 2013/07/12 21:09:58]

What does the lock protect? Can you document that?
ISTM it protects on_battery_power_ but not suspended_, meaning suspended_ should
only be accessed from one thread - which one? Can you document that?
It also looks like IsOnBatteryPowerImpl is called with the lock held, meaning
the implementation should not call other methods that will take the lock again,
such as IsOnBatteryPower, UpdateOnBatteryPower or ProcessPowerEvent. Can you
document that?

[bajones, 2013/07/13 00:33:20]

IsOnBatteryPowerImpl is now called outside of the lock.

[piman, 2013/07/15 20:51:30]

ping.

+
+  DISALLOW_COPY_AND_ASSIGN(PowerMonitorSource);
+};
+
+}  // namespace base
+
+#endif  // BASE_POWER_MONITOR_POWER_MONITOR_SOURCE_H_