Attempting to resolve a race condition with PowerMonitor

base/power_monitor/power_monitor.h

 // 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_H_
 #define BASE_POWER_MONITOR_POWER_MONITOR_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list_threadsafe.h"
 #include "base/power_monitor/power_observer.h"
+#include "base/synchronization/lock.h"
 
 namespace base {
 
 class PowerMonitorSource;
 
 // A class used to monitor the power state change and notify the observers about
 // the change event.
 class BASE_EXPORT PowerMonitor {
  public:
   // Takes ownership of |source|.
-  explicit PowerMonitor(scoped_ptr<PowerMonitorSource> source);
-  ~PowerMonitor();
+  static void Initialize(scoped_ptr<PowerMonitorSource> source);
+  static void Shutdown();
 
-  // Get the process-wide PowerMonitor (if not present, returns NULL).
-  static PowerMonitor* Get();
+  // Has the PowerMonitor already been initialized?
+  static bool IsInitialized();
 
   // Add and remove an observer.
   // Can be called from any thread.
   // Must not be called from within a notification callback.
-  void AddObserver(PowerObserver* observer);
-  void RemoveObserver(PowerObserver* observer);
+  static bool AddObserver(PowerObserver* observer);
+  static bool RemoveObserver(PowerObserver* observer);
 
   // Is the computer currently on battery power.
-  bool IsOnBatteryPower();
+  static bool IsOnBatteryPower();
 
  private:
+  explicit PowerMonitor(scoped_ptr<PowerMonitorSource> source);
+  ~PowerMonitor();
   friend class PowerMonitorSource;
 
+  static Lock* GetSingletonLock();
+  // Must manually aqcuire the lock before calling
+  static PowerMonitor* GetSingleton();
+
+  void AddObserverImpl(PowerObserver* observer);
+  void RemoveObserverImpl(PowerObserver* observer);
+  // Is the computer currently on battery power.
+  bool IsOnBatteryPowerImpl();
+
   PowerMonitorSource* Source();
 
   void NotifyPowerStateChange(bool battery_in_use);
   void NotifySuspend();
   void NotifyResume();
 
   scoped_refptr<ObserverListThreadSafe<PowerObserver> > observers_;
   scoped_ptr<PowerMonitorSource> source_;
 
   DISALLOW_COPY_AND_ASSIGN(PowerMonitor);
 };
 
 }  // namespace base
 
 #endif  // BASE_POWER_MONITOR_POWER_MONITOR_H_