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

base/system_monitor/system_monitor.cc

 // Copyright (c) 2012 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.
 
 #include "base/system_monitor/system_monitor.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/message_loop.h"
@@ skipping 21 matching lines @@
     : device_id(id),
       name(device_name),
       location(device_location) {
 }
 
 SystemMonitor::SystemMonitor()
     : power_observer_list_(new ObserverListThreadSafe<PowerObserver>()),
       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;
 
   DCHECK(MessageLoop::current());
 #if defined(ENABLE_BATTERY_MONITORING)
   delayed_battery_check_.Start(FROM_HERE,
       base::TimeDelta::FromMilliseconds(kDelayedBatteryCheckMs), this,
       &SystemMonitor::BatteryCheck);
 #endif  // defined(ENABLE_BATTERY_MONITORING)
 #if defined(OS_MACOSX)
@@ skipping 61 matching lines @@
 }
 
 void SystemMonitor::ProcessRemovableStorageDetached(const std::string& id) {
   RemovableStorageMap::iterator it = removable_storage_map_.find(id);
   if (it == removable_storage_map_.end())
     return;
   removable_storage_map_.erase(it);
   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;
   for (RemovableStorageMap::const_iterator it = removable_storage_map_.begin();
        it != removable_storage_map_.end();
        ++it) {
     results.push_back(it->second);
   }
   return results;
 }
 
 void SystemMonitor::AddPowerObserver(PowerObserver* obs) {
   power_observer_list_->AddObserver(obs);
 }
 
 void SystemMonitor::RemovePowerObserver(PowerObserver* obs) {
   power_observer_list_->RemoveObserver(obs);
 }
 
 void SystemMonitor::AddDevicesChangedObserver(DevicesChangedObserver* obs) {
   devices_changed_observer_list_->AddObserver(obs);
 }
 
 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(
       &DevicesChangedObserver::OnDevicesChanged, device_type);
 }
 
 void SystemMonitor::NotifyRemovableStorageAttached(
     const std::string& id,
     const string16& name,
     const FilePath::StringType& location) {
@@ skipping 24 matching lines @@
 void SystemMonitor::NotifyResume() {
   DVLOG(1) << "Power Resuming";
   power_observer_list_->Notify(&PowerObserver::OnResume);
 }
 
 void SystemMonitor::BatteryCheck() {
   ProcessPowerMessage(SystemMonitor::POWER_STATE_EVENT);
 }
 
 }  // namespace base