refactor EnumerateDevices to make it a persistent request.

content/browser/renderer_host/media/media_stream_manager.h

 // 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.
 
 // MediaStreamManager is used to open/enumerate media capture devices (video
 // supported now). Call flow:
 // 1. GenerateStream is called when a render process wants to use a capture
 //    device.
 // 2. MediaStreamManager will ask MediaStreamDeviceSettings for permission to
 //    use devices and for which device to use.
@@ skipping 12 matching lines @@
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_MEDIA_STREAM_MANAGER_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop.h"
+#include "base/system_monitor/system_monitor.h"
 #include "base/threading/thread.h"
 #include "content/browser/renderer_host/media/media_stream_provider.h"
 #include "content/browser/renderer_host/media/media_stream_settings_requester.h"
 #include "content/common/media/media_stream_options.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_thread.h"
 
 namespace base {
 namespace win {
 class ScopedCOMInitializer;
@@ skipping 22 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(DeviceThread);
 };
 
 // MediaStreamManager is used to generate and close new media devices, not to
 // start the media flow.
 // The classes requesting new media streams are answered using
 // MediaStreamManager::Listener.
 class CONTENT_EXPORT MediaStreamManager
     : public MediaStreamProviderListener,
       public MessageLoop::DestructionObserver,
-      public SettingsRequester {
+      public SettingsRequester,
+      public base::SystemMonitor::DevicesChangedObserver {
  public:
   // This class takes the ownerships of the |audio_input_device_manager|
   // and |video_capture_manager|.
   MediaStreamManager(AudioInputDeviceManager* audio_input_device_manager,
                      VideoCaptureManager* video_capture_manager);
 
   virtual ~MediaStreamManager();
 
   // Used to access VideoCaptureManager.
   VideoCaptureManager* video_capture_manager();
@@ skipping 14 matching lines @@
 
   // Cancel generate stream.
   void CancelGenerateStream(const std::string& label);
 
   // Closes generated stream.
   void StopGeneratedStream(const std::string& label);
 
   // Gets a list of devices of |type|.
   // The request is identified using |label|, which is pointing to a
   // std::string.
+  // The request is persistent, which means the client keeps listening to
+  // device changes, such as plug/unplug, and expects new device list for
+  // such a change, till the client stops the request.
   void EnumerateDevices(MediaStreamRequester* requester,
                         int render_process_id,
                         int render_view_id,
                         MediaStreamType type,
                         const GURL& security_origin,
                         std::string* label);
 
   // Open a device identified by |device_id|.
   // The request is identified using |label|, which is pointing to a
   // std::string.
@@ skipping 14 matching lines @@
                                  const StreamDeviceInfoArray& devices) OVERRIDE;
   virtual void Error(MediaStreamType stream_type,
                      int capture_session_id,
                      MediaStreamProviderError error) OVERRIDE;
 
   // Implements SettingsRequester.
   virtual void DevicesAccepted(const std::string& label,
                                const StreamDeviceInfoArray& devices) OVERRIDE;
   virtual void SettingsError(const std::string& label) OVERRIDE;
 
+  // Implements base::SystemMonitor::DevicesChangedObserver.
+  virtual void OnDevicesChanged(base::SystemMonitor::DeviceType device_type);
+
   // Used by unit test to make sure fake devices are used instead of a real
   // devices, which is needed for server based testing.
   // TODO(xians): Remove this hack since we can create our own
   // MediaStreamManager in our unit tests.
   void UseFakeDevice();
 
   // This object gets deleted on the UI thread after the IO thread has been
   // destroyed. So we need to know when IO thread is being destroyed so that
   // we can delete VideoCaptureManager and AudioInputDeviceManager.
   virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
 
  private:
   // Contains all data needed to keep track of requests.
   struct DeviceRequest;
 
+  // Cache enumerated device list.
+  struct EnumerationCache {
+    EnumerationCache();
+
+    bool valid;
+    StreamDeviceInfoArray devices;
+  };
+
   // Helpers for signaling the media observer that new capture devices are
   // opened/closed.
   void NotifyObserverDevicesOpened(DeviceRequest* request);
   void NotifyObserverDevicesClosed(DeviceRequest* request);
   void DevicesFromRequest(DeviceRequest* request,
                           content::MediaStreamDevices* devices);
 
   // Helpers.
   bool RequestDone(const MediaStreamManager::DeviceRequest& request) const;
   MediaStreamProvider* GetDeviceManager(MediaStreamType stream_type);
   void StartEnumeration(DeviceRequest* new_request,
                         std::string* label);
+  void AddRequest(DeviceRequest* new_request, std::string* label);
+  bool HasEnumerationRequest(MediaStreamType type);
+  bool HasEnumerationRequest();
+  void ClearEnumerationCache(EnumerationCache* cache);
 
   // Helper to ensure the device thread and pass the message loop to device
   // managers, it also register itself as the listener to the device managers.
   void EnsureDeviceThreadAndListener();
 
+  // Sends cached device list to a client corresponding to the request
+  // identified by |label|.
+  void SendCachedDeviceList(EnumerationCache* cache, const std::string& label);
+
+  // Stop the request of enumerating devices indentified by |label|.
+  void StopEnumerateDevices(const std::string& label);
+
+  // Helpers to start and stop monitoring devices.
+  void StartMonitoring();
+  void StopMonitoring();
+
   // Device thread shared by VideoCaptureManager and AudioInputDeviceManager.
   scoped_ptr<base::Thread> device_thread_;
 
   scoped_ptr<MediaStreamDeviceSettings> device_settings_;
   scoped_refptr<AudioInputDeviceManager> audio_input_device_manager_;
   scoped_refptr<VideoCaptureManager> video_capture_manager_;
 
+  // Indicator of device monitoring state.
+  bool monitoring_started_;
+
+  // Stores most recently enumerated device lists. The cache is cleared when
+  // monitoring is stopped or there is request for that type of devices.
+  EnumerationCache audio_enumeration_cache_;
+  EnumerationCache video_enumeration_cache_;
+
   // Keeps track of device types currently being enumerated to not enumerate
   // when not necessary.
   std::vector<bool> enumeration_in_progress_;
 
   // All non-closed request.
   typedef std::map<std::string, DeviceRequest> DeviceRequests;
   DeviceRequests requests_;
 
   // Hold a pointer to the IO loop to check we delete the device thread and
   // managers on the right thread.
   MessageLoop* io_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaStreamManager);
 };
 
 }  // namespace media_stream
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_MEDIA_STREAM_MANAGER_H_