output_plugin: added method "drain"

drain() is the opposite of cancel(): it waits until all data in the
buffer has finished playing.  Instead of implicitly draining in the
close() method like the ALSA plugin has been doing it forever, let the
output thread decide whether to drain or to cancel.

src/output/alsa_plugin.c

@@ -495,6 +495,14 @@ alsa_recover(struct alsa_data *ad, int err)
 	return err;
 }
 
+static void
+alsa_drain(void *data)
+{
+	struct alsa_data *ad = data;
+
+	snd_pcm_drain(ad->pcm);
+}
+
 static void
 alsa_cancel(void *data)
 {
@@ -508,9 +516,6 @@ alsa_close(void *data)
 {
 	struct alsa_data *ad = data;
 
-	if (snd_pcm_state(ad->pcm) == SND_PCM_STATE_RUNNING)
-		snd_pcm_drain(ad->pcm);
-
 	snd_pcm_close(ad->pcm);
 }
 
@@ -542,6 +547,7 @@ const struct audio_output_plugin alsaPlugin = {
 	.finish = alsa_finish,
 	.open = alsa_open,
 	.play = alsa_play,
+	.drain = alsa_drain,
 	.cancel = alsa_cancel,
 	.close = alsa_close,
 

src/output_plugin.h

@@ -116,6 +116,11 @@ struct audio_output_plugin {
 	size_t (*play)(void *data, const void *chunk, size_t size,
 		       GError **error);
 
+	/**
+	 * Wait until the device has finished playing.
+	 */
+	void (*drain)(void *data);
+
 	/**
 	 * Try to cancel data which may still be in the device's
 	 * buffers.
@@ -213,6 +218,13 @@ ao_plugin_play(const struct audio_output_plugin *plugin,
 	return plugin->play(data, chunk, size, error);
 }
 
+static inline void
+ao_plugin_drain(const struct audio_output_plugin *plugin, void *data)
+{
+	if (plugin->drain != NULL)
+		plugin->drain(data);
+}
+
 static inline void
 ao_plugin_cancel(const struct audio_output_plugin *plugin, void *data)
 {

src/output_thread.c

@@ -62,13 +62,13 @@ ao_enable(struct audio_output *ao)
 }
 
 static void
-ao_close(struct audio_output *ao);
+ao_close(struct audio_output *ao, bool drain);
 
 static void
 ao_disable(struct audio_output *ao)
 {
 	if (ao->open)
-		ao_close(ao);
+		ao_close(ao, false);
 
 	if (ao->really_enabled) {
 		ao->really_enabled = false;
@@ -151,7 +151,7 @@ ao_open(struct audio_output *ao)
 }
 
 static void
-ao_close(struct audio_output *ao)
+ao_close(struct audio_output *ao, bool drain)
 {
 	assert(ao->open);
 
@@ -162,6 +162,11 @@ ao_close(struct audio_output *ao)
 	ao->open = false;
 	g_mutex_unlock(ao->mutex);
 
+	if (drain)
+		ao_plugin_drain(ao->plugin, ao->data);
+	else
+		ao_plugin_cancel(ao->plugin, ao->data);
+
 	ao_plugin_close(ao->plugin, ao->data);
 	filter_close(ao->filter);
 
@@ -208,7 +213,7 @@ ao_reopen(struct audio_output *ao)
 	if (!audio_format_fully_defined(&ao->config_audio_format)) {
 		if (ao->open) {
 			const struct music_pipe *mp = ao->pipe;
-			ao_close(ao);
+			ao_close(ao, true);
 			ao->pipe = mp;
 		}
 
@@ -253,8 +258,7 @@ ao_play_chunk(struct audio_output *ao, const struct music_chunk *chunk)
 			  ao->name, ao->plugin->name, error->message);
 		g_error_free(error);
 
-		ao_plugin_cancel(ao->plugin, ao->data);
-		ao_close(ao);
+		ao_close(ao, false);
 
 		/* don't automatically reopen this device for 10
 		   seconds */
@@ -273,8 +277,7 @@ ao_play_chunk(struct audio_output *ao, const struct music_chunk *chunk)
 				  ao->name, ao->plugin->name, error->message);
 			g_error_free(error);
 
-			ao_plugin_cancel(ao->plugin, ao->data);
-			ao_close(ao);
+			ao_close(ao, false);
 
 			/* don't automatically reopen this device for
 			   10 seconds */
@@ -344,7 +347,7 @@ static void ao_pause(struct audio_output *ao)
 	do {
 		ret = ao_plugin_pause(ao->plugin, ao->data);
 		if (!ret) {
-			ao_close(ao);
+			ao_close(ao, false);
 			break;
 		}
 	} while (ao->command == AO_COMMAND_NONE);
@@ -385,8 +388,7 @@ static gpointer audio_output_task(gpointer arg)
 			assert(ao->open);
 			assert(ao->pipe != NULL);
 
-			ao_plugin_cancel(ao->plugin, ao->data);
-			ao_close(ao);
+			ao_close(ao, false);
 			ao_command_finished(ao);
 			break;