Attempting to resolve a race condition with PowerMonitor

base/power_monitor/power_monitor.cc

Index: base/power_monitor/power_monitor.cc
diff --git a/base/power_monitor/power_monitor.cc b/base/power_monitor/power_monitor.cc
index 14dc4b517832785c07153abfed2bcc4a3a738940..b5902db5fa1c85b21ebd2a0d9aa12c440160ed46 100644
--- a/base/power_monitor/power_monitor.cc
+++ b/base/power_monitor/power_monitor.cc
@@ -3,34 +3,66 @@
 // found in the LICENSE file.
 
 #include "base/power_monitor/power_monitor.h"
+
+#include "base/lazy_instance.h"
 #include "base/power_monitor/power_monitor_source.h"
+#include "base/synchronization/lock.h"
 
 namespace base {
 
+LazyInstance<Lock>::Leaky g_power_monitor_lock = LAZY_INSTANCE_INITIALIZER;
 static PowerMonitor* g_power_monitor = NULL;
 
+PowerMonitor* PowerMonitor::Create(scoped_ptr<PowerMonitorSource> source) {
+  AutoLock(g_power_monitor_lock.Get());
+  return new PowerMonitor(source.Pass());
+}
+
 PowerMonitor::PowerMonitor(scoped_ptr<PowerMonitorSource> source)
     : observers_(new ObserverListThreadSafe<PowerObserver>()),
       source_(source.Pass()) {
+  g_power_monitor_lock.Get().AssertAcquired();
   DCHECK(!g_power_monitor);
   g_power_monitor = this;
 }
 
 PowerMonitor::~PowerMonitor() {
+  AutoLock(g_power_monitor_lock.Get());
   DCHECK_EQ(this, g_power_monitor);
   g_power_monitor = NULL;
 }
 
 // static
 PowerMonitor* PowerMonitor::Get() {
+  AutoLock(g_power_monitor_lock.Get());
   return g_power_monitor;
 }
 
+// static
+bool PowerMonitor::AddObserverThreadSafe(PowerObserver* observer) {
+  AutoLock(g_power_monitor_lock.Get());
+  if (!g_power_monitor)
+    return false;
+  g_power_monitor->RemoveObserver(observer);
+  return true;
+}
+
+// static
+bool PowerMonitor::RemoveObserverThreadSafe(PowerObserver* observer) {
+  AutoLock(g_power_monitor_lock.Get());
+  if (!g_power_monitor)
+    return false;
+  g_power_monitor->RemoveObserver(observer);
+  return true;
+}
+
 void PowerMonitor::AddObserver(PowerObserver* obs) {
+  g_power_monitor_lock.Get().AssertAcquired();
   observers_->AddObserver(obs);
 }
 
 void PowerMonitor::RemoveObserver(PowerObserver* obs) {
+  g_power_monitor_lock.Get().AssertAcquired();
   observers_->RemoveObserver(obs);
 }
 
@@ -45,16 +77,19 @@ bool PowerMonitor::IsOnBatteryPower() {
 void PowerMonitor::NotifyPowerStateChange(bool battery_in_use) {
   DVLOG(1) << "PowerStateChange: " << (battery_in_use ? "On" : "Off")
            << " battery";
+  AutoLock(g_power_monitor_lock.Get());
   observers_->Notify(&PowerObserver::OnPowerStateChange, battery_in_use);
 }
 
 void PowerMonitor::NotifySuspend() {
   DVLOG(1) << "Power Suspending";
+  AutoLock(g_power_monitor_lock.Get());
   observers_->Notify(&PowerObserver::OnSuspend);
 }
 
 void PowerMonitor::NotifyResume() {
   DVLOG(1) << "Power Resuming";
+  AutoLock(g_power_monitor_lock.Get());
   observers_->Notify(&PowerObserver::OnResume);
 }