audio_output: workaround for deadlock

During debugging, I found a deadlock between flushAudioBuffer() and
the audio_output_task(): audio_output_task() didn't notice that there
is a command, and flushAudioBuffer() waited forever in notify_wait().
I am not sure yet what is the real cause; work around this for now by
waking up non-finished audio outputs in every iteration.

src/audio.c

@@ -281,7 +281,7 @@ static int flushAudioBuffer(void)
 		int finished = 1;
 
 		for (i = 0; i < audioOutputArraySize; ++i) {
-			const struct audio_output *ao = &audioOutputArray[i];
+			struct audio_output *ao = &audioOutputArray[i];
 
 			if (!audio_output_is_open(ao))
 				continue;
@@ -295,8 +295,10 @@ static int flushAudioBuffer(void)
 					   closed if the play func
 					   returned an error */
 					audioDeviceStates[i] = DEVICE_ENABLE;
-			} else
+			} else {
 				finished = 0;
+				audio_output_signal(ao);
+			}
 		}
 
 		if (finished)

src/output_control.c

@@ -86,6 +86,12 @@ int audio_output_open(struct audio_output *audioOutput,
 	return ret;
 }
 
+void
+audio_output_signal(struct audio_output *ao)
+{
+	notify_signal(&ao->notify);
+}
+
 void audio_output_play(struct audio_output *audioOutput,
 		       const char *playChunk, size_t size)
 {

src/output_control.h

@@ -30,6 +30,15 @@ struct tag;
 int audio_output_init(struct audio_output *, ConfigParam * param);
 int audio_output_open(struct audio_output *audioOutput,
 		      const struct audio_format *audioFormat);
+
+/**
+ * Wakes up the audio output thread.  This is part of a workaround for
+ * a deadlock bug, and should be removed as soon as the real cause is
+ * fixed.  XXX
+ */
+void
+audio_output_signal(struct audio_output *ao);
+
 void audio_output_play(struct audio_output *audioOutput,
 		       const char *playChunk, size_t size);
 void audio_output_cancel(struct audio_output *audioOutput);