output/Internal: add attribute request.audio_format

Make in_audio_format accessible only from within the OutputThread, and
add a new one for inter-thread communication.

src/output/Internal.hxx

@@ -166,6 +166,8 @@ struct AudioOutput {
 	/**
 	 * The audio_format in which audio data is received from the
 	 * player thread (which in turn receives it from the decoder).
+	 *
+	 * Only accessible from within the OutputThread.
 	 */
 	AudioFormat in_audio_format;
 
@@ -246,6 +248,16 @@ struct AudioOutput {
 	 */
 	Command command = Command::NONE;
 
+	/**
+	 * Additional data for #command.  Protected by #mutex.
+	 */
+	struct Request {
+		/**
+		 * The #AudioFormat requested by #Command::OPEN.
+		 */
+		AudioFormat audio_format;
+	} request;
+
 	/**
 	 * This mutex protects #open, #fail_timer, #pipe.
 	 */

src/output/OutputControl.cxx

@@ -112,7 +112,7 @@ AudioOutput::Open(const AudioFormat audio_format, const MusicPipe &mp)
 
 	fail_timer.Reset();
 
-	if (open && audio_format == in_audio_format) {
+	if (open && audio_format == request.audio_format) {
 		assert(&pipe.GetPipe() == &mp || (always_on && pause));
 
 		if (pause) {
@@ -131,7 +131,7 @@ AudioOutput::Open(const AudioFormat audio_format, const MusicPipe &mp)
 		return true;
 	}
 
-	in_audio_format = audio_format;
+	request.audio_format = audio_format;
 
 	pipe.Init(mp);
 

src/output/OutputThread.cxx

@@ -134,7 +134,7 @@ inline void
 AudioOutput::Open()
 {
 	assert(!open);
-	assert(in_audio_format.IsValid());
+	assert(request.audio_format.IsValid());
 
 	fail_timer.Reset();
 
@@ -144,6 +144,8 @@ AudioOutput::Open()
 		/* still no luck */
 		return;
 
+	in_audio_format = request.audio_format;
+
 	bool success;
 
 	{