Extend the capability of SystemMonitor to support watching storage free space change

base/system_monitor/system_monitor.cc

Index: base/system_monitor/system_monitor.cc
diff --git a/base/system_monitor/system_monitor.cc b/base/system_monitor/system_monitor.cc
index f30c8935c9a999b38382f78e879c9319a4eba13f..acc82ff3b722e942bff8b1a274128570e57ffc45 100644
--- a/base/system_monitor/system_monitor.cc
+++ b/base/system_monitor/system_monitor.cc
@@ -39,7 +39,8 @@ SystemMonitor::SystemMonitor()
       devices_changed_observer_list_(
           new ObserverListThreadSafe<DevicesChangedObserver>()),
       battery_in_use_(false),
-      suspended_(false) {
+      suspended_(false),
+      free_space_notification_(NULL) {
   DCHECK(!g_system_monitor);
   g_system_monitor = this;
 
@@ -121,6 +122,14 @@ void SystemMonitor::ProcessRemovableStorageDetached(const std::string& id) {
   NotifyRemovableStorageDetached(id);
 }
 
+void SystemMonitor::ProcessStorageFreeSpaceChanged(
+    const FilePath::StringType& path) {
+  DVLOG(1) << "Free Space Changing: " << path;
+  if (free_space_changed_observer_map_[path].get())

[vandebo (ex-Chrome), 2012/09/11 22:49:27]

Use find(path) so that you don't add something to the map that was just deleted.

[Hongbo Min, 2012/09/12 09:24:31]

Done.

+    free_space_changed_observer_map_[path]->Notify(
+        &StorageFreeSpaceChangedObserver::OnStorageFreeSpaceChanged, path);
+}
+
 std::vector<SystemMonitor::RemovableStorageInfo>
 SystemMonitor::GetAttachedRemovableStorage() const {
   std::vector<RemovableStorageInfo> results;
@@ -148,6 +157,38 @@ void SystemMonitor::RemoveDevicesChangedObserver(DevicesChangedObserver* obs) {
   devices_changed_observer_list_->RemoveObserver(obs);
 }
 
+void SystemMonitor::AddStorageFreeSpaceChangedObserver(
+    const FilePath::StringType& path,
+    StorageFreeSpaceChangedObserver* obs) {
+
+  // Try to start watching the storage.
+  if (watching_storage_set_.find(path) == watching_storage_set_.end() &&
+      !free_space_notification_->StartWatchingStorage(path))

[vandebo (ex-Chrome), 2012/09/11 22:49:27]

Make this two different if's to make it more readable.

[Hongbo Min, 2012/09/12 09:24:31]

Done.

+      return;
+
+  watching_storage_set_.insert(path);
+  if (!free_space_changed_observer_map_[path].get())
+    free_space_changed_observer_map_[path] =
+        new StorageFreeSpaceChangedObserverList();
+
+  free_space_changed_observer_map_[path]->AddObserver(obs);

[vandebo (ex-Chrome), 2012/09/11 22:49:27]

Once you have a lock, I think you'll want to add the observer before calling
StartWatchingStorage

[Hongbo Min, 2012/09/12 09:24:31]

It can avoid the lock occupied too much time in case of the StartWatchingStorage
is a time-consuming operation, right?

For StartWatchingStorage calling, it starts out of the lock scope since
IsWatchingStorage is used. But for StopWatchingStorage, the calling timing is
when the observer list for a storage path becomes empty, it also implies thread
synchronization arose from the observer mpa and can not move out of the lock
scope to avoid multi-thread issue, e.g. in case of stop watching in one thread
but it already starts watching again in another thread.

+}
+
+void SystemMonitor::RemoveStorageFreeSpaceChangedObserver(
+    const FilePath::StringType& path,
+    StorageFreeSpaceChangedObserver* obs) {
+  size_t count = watching_storage_set_.count(path);
+  if (count == 0)
+    return;
+
+  // Stop watching the storage in case of the last observer is removed.
+  if (count == 1)
+    free_space_notification_->StopWatchingStorage(path);
+
+  free_space_changed_observer_map_[path]->RemoveObserver(obs);
+  watching_storage_set_.erase(path);
+}
+
 void SystemMonitor::NotifyDevicesChanged(DeviceType device_type) {
   DVLOG(1) << "DevicesChanged with device type " << device_type;
   devices_changed_observer_list_->Notify(