Queue commands to the Os to start a video device.

content/browser/renderer_host/media/video_capture_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.
 
 // VideoCaptureManager is used to open/close, start/stop, enumerate available
 // video capture devices, and manage VideoCaptureController's.
 // All functions are expected to be called from Browser::IO thread. Some helper
 // functions (*OnDeviceThread) will dispatch operations to the device thread.
 // VideoCaptureManager will open OS dependent instances of VideoCaptureDevice.
 // A device can only be opened once.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_MANAGER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_MANAGER_H_
 
+#include <list>
 #include <map>
 #include <set>
 #include <string>
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/process/process_handle.h"
 #include "base/timer/elapsed_timer.h"
 #include "content/browser/renderer_host/media/media_stream_provider.h"
@@ skipping 150 matching lines @@
   // Consolidates the cached devices list with the list of currently connected
   // devices in the system |names_snapshot|. Retrieves the supported formats of
   // the new devices and sends the new cache to OnDevicesInfoEnumerated().
   void ConsolidateDevicesInfoOnDeviceThread(
       base::Callback<void(const media::VideoCaptureDeviceInfos&)>
           on_devices_enumerated_callback,
       MediaStreamType stream_type,
       const media::VideoCaptureDeviceInfos& old_device_info_cache,
       scoped_ptr<media::VideoCaptureDevice::Names> names_snapshot);
 
+  // On the OS level, starting a capture device can take 1-2 seconds.
+  // To avoid multiple unnecessary start/stop commands to the OS, each start
+  // request is queued in |device_start_queue_|.
+  // QueueStartDevice creates a new entry in |device_start_queue_| and posts a
+  // request to start |entry| on the device thread unless there is another
+  // request pending start.
+  void QueueStartDevice(media::VideoCaptureSessionId session_id,
+                        DeviceEntry* entry,

[tommi (sloooow) - chröme, 2014/12/15 16:25:05]

can you document the ownership/lifetime of |entry|?

+                        const media::VideoCaptureParams& params);
+  void OnDeviceStarted();
+  void DoStopDevice(DeviceEntry* entry, bool delete_entry);
+  void HandleQueuedStartRequest();
+
   // Creates and Starts a new VideoCaptureDevice, storing the result in
   // |entry->video_capture_device|. Ownership of |client| passes to
   // the device.
   void DoStartDeviceOnDeviceThread(
       media::VideoCaptureSessionId session_id,
       DeviceEntry* entry,
       const media::VideoCaptureParams& params,
       scoped_ptr<media::VideoCaptureDevice::Client> client);
 
   // Stops and destroys the VideoCaptureDevice held in
@@ skipping 43 matching lines @@
     const MediaStreamType stream_type;
     const std::string id;
 
     // The controller. Only used from the IO thread.
     scoped_ptr<VideoCaptureController> video_capture_controller;
 
     // The capture device. Only used from the device thread.
     scoped_ptr<media::VideoCaptureDevice> video_capture_device;
   };
   typedef std::set<DeviceEntry*> DeviceEntries;
+  // Currently opened devices. The device may or may not be started.
   DeviceEntries devices_;
 
+  // On the OS level, starting a capture device can take 1-2 seconds.
+  // To avoid multiple unnecessary start/stop commands to the OS, each start
+  // request is queued in a CaptureDeviceStartRequest.
+  struct CaptureDeviceStartRequest {
+    CaptureDeviceStartRequest(DeviceEntry* device_entry,
+                              media::VideoCaptureSessionId session_id,
+                              const media::VideoCaptureParams& params);
+
+    DeviceEntry* device_entry;

[tommi (sloooow) - chröme, 2014/12/15 16:25:05]

ownership/scope?

+    media::VideoCaptureSessionId session_id;
+    media::VideoCaptureParams params;
+  };
+  typedef std::list<CaptureDeviceStartRequest> DeviceStartQueue;
+  DeviceStartQueue device_start_queue_;
+
   // Device creation factory injected on construction from MediaStreamManager or
   // from the test harness.
   scoped_ptr<media::VideoCaptureDeviceFactory> video_capture_device_factory_;
 
   // Local cache of the enumerated video capture devices' names and capture
   // supported formats. A snapshot of the current devices and their capabilities
   // is composed in VideoCaptureDeviceFactory::EnumerateDeviceNames() and
   // ConsolidateDevicesInfoOnDeviceThread(), and this snapshot is used to update
   // this list in OnDevicesInfoEnumerated(). GetDeviceSupportedFormats() will
   // use this list if the device is not started, otherwise it will retrieve the
   // active device capture format from the VideoCaptureController associated.
   media::VideoCaptureDeviceInfos devices_info_cache_;
 
   // Accessed on the device thread only.
   std::map<media::VideoCaptureSessionId, gfx::NativeViewId>
       notification_window_ids_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_MANAGER_H_