Harden audio output controller making it safe to call Pause() before

media/audio/audio_output_controller.h

 // Copyright (c) 2011 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.
 
 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "base/time.h"
 #include "media/audio/audio_buffers_state.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_manager.h"
 #include "media/audio/simple_sources.h"
 
 class MessageLoop;
 
 // An AudioOutputController controls an AudioOutputStream and provides data
 // to this output stream. It has an important function that it executes
 // audio operations like play, pause, stop, etc. on a separate thread,
 // namely the audio controller thread.
 //
 // All the public methods of AudioOutputController are non-blocking except
 // close, the actual operations are performed on the audio controller thread.
 //
-// Here is a state diagram for the AudioOutputController:
+// Here is a state diagram for the AudioOutputController for default low
+// latency mode; in normal latency mode there is no "starting" or "paused when
+// starting" states, "created" immediately switches to "playing":
 //
-//                    .---->  [ Closed / Error ]  <------.
-//                    |                ^                 |
-//                    |                |                 |
-//               [ Created ]  -->  [ Playing ]  -->  [ Paused ]
-//                    ^                ^                 |
-//                    |                |                 |
-//              *[  Empty  ]           `-----------------'
+//             .----------------------->  [ Closed / Error ]  <------.
+//             |                                   ^                 |
+//             |                                   |                 |
+//        [ Created ]  -->  [ Starting ]  -->  [ Playing ]  -->  [ Paused ]
+//             ^                 |                 ^                |  ^
+//             |                 |                 |                |  |
+//             |                 |                 `----------------'  |
+//             |                 V                                     |
+//             |        [ PausedWhenStarting ] ------------------------'
+//             |
+//       *[  Empty  ]
 //
 // * Initial state
 //
 // There are two modes of buffering operations supported by this class.
 //
 // Regular latency mode:
 //   In this mode we receive signals from AudioOutputController and then we
 //   enqueue data into it.
 //
 // Low latency mode:
 //   In this mode a DataSource object is given to the AudioOutputController
 //   and AudioOutputController reads from it synchronously.
 //
 #include "media/base/media_export.h"
 
 namespace media {
 
 class MEDIA_EXPORT AudioOutputController
     : public base::RefCountedThreadSafe<AudioOutputController>,
       public AudioOutputStream::AudioSourceCallback {
  public:
-  // Internal state of the source.
-  enum State {
-    kEmpty,
-    kCreated,
-    kPlaying,
-    kPaused,
-    kClosed,
-    kError,
-  };
-
   // Value sent by the controller to the renderer in low-latency mode
   // indicating that the stream is paused.
   static const int kPauseMark;
 
   // An event handler that receives events from the AudioOutputController. The
   // following methods are called on the audio controller thread.
   class MEDIA_EXPORT EventHandler {
    public:
     virtual ~EventHandler() {}
     virtual void OnCreated(AudioOutputController* controller) = 0;
@@ skipping 84 matching lines @@
   void EnqueueData(const uint8* data, uint32 size);
 
   bool LowLatencyMode() const { return sync_reader_ != NULL; }
 
   ///////////////////////////////////////////////////////////////////////////
   // AudioSourceCallback methods.
   virtual uint32 OnMoreData(AudioOutputStream* stream, uint8* dest,
                             uint32 max_size, AudioBuffersState buffers_state);
   virtual void OnError(AudioOutputStream* stream, int code);
 
+ protected:
+    // Internal state of the source.
+  enum State {
+    kEmpty,
+    kCreated,
+    kPlaying,
+    kStarting,
+    kPausedWhenStarting,
+    kPaused,
+    kClosed,
+    kError,
+  };
+
  private:
   // We are polling sync reader if data became available.
   static const int kPollNumAttempts;
   static const int kPollPauseInMilliseconds;
 
   AudioOutputController(EventHandler* handler,
                         uint32 capacity, SyncReader* sync_reader);
 
   // The following methods are executed on the audio controller thread.
   void DoCreate(const AudioParameters& params);
@@ skipping 41 matching lines @@
   // When starting stream we wait for data to become available.
   // Number of times left.
   int number_polling_attempts_left_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputController);
 };
 
 }  // namespace media
 
 #endif  //  MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_