output: added option "always_on" for radio stations

doc/user.xml

@@ -339,6 +339,18 @@ cd mpd-version</programlisting>
             </row>
             <row>
               <entry>
+                <varname>always_on</varname>
+                  <parameter>yes|no</parameter>
+              </entry>
+              <entry>
+                If set to "yes", then MPD attempts to keep this audio
+                output always open.  This may be useful for streaming
+                servers, when you don't want to disconnect all
+                listeners even when playback is accidently stopped.
+              </entry>
+            </row>
+            <row>
+              <entry>
                 <varname>mixer_type</varname>
                 <parameter>hardware|software|none</parameter>
               </entry>

src/output_all.c

@@ -559,6 +559,29 @@ audio_output_all_close(void)
 }
 
 void
+audio_output_all_release(void)
+{
+	unsigned int i;
+
+	for (i = 0; i < num_audio_outputs; ++i)
+		audio_output_release(&audio_outputs[i]);
+
+	if (g_mp != NULL) {
+		assert(g_music_buffer != NULL);
+
+		music_pipe_clear(g_mp, g_music_buffer);
+		music_pipe_free(g_mp);
+		g_mp = NULL;
+	}
+
+	g_music_buffer = NULL;
+
+	audio_format_clear(&input_audio_format);
+
+	audio_output_all_elapsed_time = -1.0;
+}
+
+void
 audio_output_all_song_border(void)
 {
 	/* clear the elapsed_time pointer at the beginning of a new

src/output_all.h

@@ -92,6 +92,13 @@ void
 audio_output_all_close(void);
 
 /**
+ * Closes all audio outputs.  Outputs with the "always_on" flag are
+ * put into pause mode.
+ */
+void
+audio_output_all_release(void);
+
+/**
  * Enqueue a #music_chunk object for playing, i.e. pushes it to a
  * #music_pipe.
  *

src/output_control.c

@@ -118,9 +118,13 @@ audio_output_open(struct audio_output *ao,
 
 	if (ao->open &&
 	    audio_format_equals(audio_format, &ao->in_audio_format)) {
-		assert(ao->pipe == mp);
+		assert(ao->pipe == mp ||
+		       (ao->always_on && ao->pause));
 
 		if (ao->pause) {
+			ao->chunk = NULL;
+			ao->pipe = mp;
+
 			/* unpause with the CANCEL command; this is a
 			   hack, but suits well for forcing the thread
 			   to leave the ao_pause() thread, and we need
@@ -266,6 +270,15 @@ void audio_output_close(struct audio_output *ao)
 	g_mutex_unlock(ao->mutex);
 }
 
+void
+audio_output_release(struct audio_output *ao)
+{
+	if (ao->always_on)
+		audio_output_pause(ao);
+	else
+		audio_output_close(ao);
+}
+
 void audio_output_finish(struct audio_output *ao)
 {
 	audio_output_close(ao);

src/output_control.h

@@ -71,7 +71,16 @@ void
 audio_output_drain_async(struct audio_output *ao);
 
 void audio_output_cancel(struct audio_output *ao);
+
 void audio_output_close(struct audio_output *ao);
+
+/**
+ * Closes the audio output, but if the "always_on" flag is set, put it
+ * into pause mode instead.
+ */
+void
+audio_output_release(struct audio_output *ao);
+
 void audio_output_finish(struct audio_output *ao);
 
 #endif

src/output_init.c

@@ -184,6 +184,7 @@ audio_output_init(struct audio_output *ao, const struct config_param *param,
 	}
 
 	ao->plugin = plugin;
+	ao->always_on = config_get_block_bool(param, "always_on", false);
 	ao->enabled = config_get_block_bool(param, "enabled", true);
 	ao->really_enabled = false;
 	ao->open = false;

src/output_internal.h

@@ -76,6 +76,12 @@ struct audio_output {
 	struct mixer *mixer;
 
 	/**
+	 * Shall this output always play something (i.e. silence),
+	 * even when playback is stopped?
+	 */
+	bool always_on;
+
+	/**
 	 * Has the user enabled this device?
 	 */
 	bool enabled;

src/player_thread.c

@@ -978,7 +978,7 @@ static gpointer player_task(G_GNUC_UNUSED gpointer arg)
 		case PLAYER_COMMAND_CLOSE_AUDIO:
 			player_unlock();
 
-			audio_output_all_close();
+			audio_output_all_release();
 
 			player_lock();
 			player_command_finished_locked();