output: one thread per audio output

To keep I/O nastiness and latencies away from the core, move the audio
output code to a separate thread, one per output.  The thread is
created on demand, and currently runs until mpd exits.

src/Makefile.am

@@ -37,6 +37,7 @@ mpd_headers = \
 	audioOutput.h \
 	output_api.h \
 	output_list.h \
+	output_thread.h \
 	output_control.h \
 	audioOutputs/audioOutput_shout.h \
 	buffer2array.h \
@@ -114,6 +115,7 @@ mpd_SOURCES = \
 	audio.c \
 	audioOutput.c \
 	output_list.c \
+	output_thread.c \
 	output_control.c \
 	output_init.c \
 	buffer2array.c \

src/output_api.h

@@ -26,6 +26,7 @@
 #include "tag.h"
 #include "conf.h"
 #include "log.h"
+#include "notify.h"
 #include "os_compat.h"
 
 #define DISABLED_AUDIO_OUTPUT_PLUGIN(plugin) const struct audio_output_plugin plugin;
@@ -54,6 +55,16 @@ struct audio_output_plugin {
 			 const struct tag *tag);
 };
 
+enum audio_output_command {
+	AO_COMMAND_NONE = 0,
+	AO_COMMAND_OPEN,
+	AO_COMMAND_CLOSE,
+	AO_COMMAND_PLAY,
+	AO_COMMAND_CANCEL,
+	AO_COMMAND_SEND_TAG,
+	AO_COMMAND_KILL
+};
+
 struct audio_output {
 	int open;
 	const char *name;
@@ -67,7 +78,22 @@ struct audio_output {
 	char *convBuffer;
 	size_t convBufferLen;
 
+	pthread_t thread;
+	struct notify notify;
+	enum audio_output_command command;
+	union {
+		struct {
+			const char *data;
+			size_t size;
+		} play;
+
+		const struct tag *tag;
+	} args;
+	int result;
+
 	void *data;
 };
 
+extern struct notify audio_output_client_notify;
+
 #endif

src/output_control.c

@@ -18,8 +18,27 @@
 
 #include "output_control.h"
 #include "output_api.h"
+#include "output_thread.h"
 #include "pcm_utils.h"
-#include "utils.h"
+
+#include <pthread.h>
+
+struct notify audio_output_client_notify = NOTIFY_INITIALIZER;
+
+static void ao_command_wait(struct audio_output *ao)
+{
+	while (ao->command != AO_COMMAND_NONE) {
+		notify_signal(&ao->notify);
+		notify_wait(&audio_output_client_notify);
+	}
+}
+
+static void ao_command(struct audio_output *ao, enum audio_output_command cmd)
+{
+	assert(ao->command == AO_COMMAND_NONE);
+	ao->command = cmd;
+	ao_command_wait(ao);
+}
 
 int audio_output_open(struct audio_output *audioOutput,
 		      const struct audio_format *audioFormat)
@@ -47,67 +66,46 @@ int audio_output_open(struct audio_output *audioOutput,
 			audio_output_close(audioOutput);
 	}
 
-	if (!audioOutput->open)
+	if (audioOutput->thread == 0)
-		ret = audioOutput->plugin->open(audioOutput);
+		audio_output_thread_start(audioOutput);
 
-	return ret;
+	if (!audioOutput->open) {
-}
+		ao_command(audioOutput, AO_COMMAND_OPEN);
-
+		ret = audioOutput->result;
-static void convertAudioFormat(struct audio_output *audioOutput,
-			       const char **chunkArgPtr, size_t *sizeArgPtr)
-{
-	size_t size = pcm_sizeOfConvBuffer(&(audioOutput->inAudioFormat),
-					   *sizeArgPtr,
-					   &(audioOutput->outAudioFormat));
-
-	if (size > audioOutput->convBufferLen) {
-		if (audioOutput->convBuffer != NULL)
-			free(audioOutput->convBuffer);
-		audioOutput->convBuffer = xmalloc(size);
-		audioOutput->convBufferLen = size;
 	}
 
-	*sizeArgPtr = pcm_convertAudioFormat(&(audioOutput->inAudioFormat), 
+	return ret;
-	                                     *chunkArgPtr, *sizeArgPtr, 
-	                                     &(audioOutput->outAudioFormat),
-	                                     audioOutput->convBuffer,
-	                                     &audioOutput->convState);
-
-	*chunkArgPtr = audioOutput->convBuffer;
 }
 
 int audio_output_play(struct audio_output *audioOutput,
 		      const char *playChunk, size_t size)
 {
-	int ret;
-
 	if (!audioOutput->open)
 		return -1;
 
-	if (!audio_format_equals(&audioOutput->inAudioFormat,
+	audioOutput->args.play.data = playChunk;
-				 &audioOutput->outAudioFormat))
+	audioOutput->args.play.size = size;
-		convertAudioFormat(audioOutput, &playChunk, &size);
+	ao_command(audioOutput, AO_COMMAND_PLAY);
 
-	ret = audioOutput->plugin->play(audioOutput, playChunk, size);
+	return audioOutput->result;
-
-	return ret;
 }
 
 void audio_output_cancel(struct audio_output *audioOutput)
 {
-	if (audioOutput->open)
+	ao_command(audioOutput, AO_COMMAND_CANCEL);
-		audioOutput->plugin->cancel(audioOutput);
 }
 
 void audio_output_close(struct audio_output *audioOutput)
 {
 	if (audioOutput->open)
-		audioOutput->plugin->close(audioOutput);
+		ao_command(audioOutput, AO_COMMAND_CLOSE);
 }
 
 void audio_output_finish(struct audio_output *audioOutput)
 {
 	audio_output_close(audioOutput);
+	if (audioOutput->thread != 0)
+		ao_command(audioOutput, AO_COMMAND_KILL);
 	if (audioOutput->plugin->finish)
 		audioOutput->plugin->finish(audioOutput);
 	if (audioOutput->convBuffer)
@@ -117,6 +115,9 @@ void audio_output_finish(struct audio_output *audioOutput)
 void audio_output_send_tag(struct audio_output *audioOutput,
 			   const struct tag *tag)
 {
-	if (audioOutput->plugin->send_tag)
+	if (audioOutput->plugin->send_tag == NULL)
-		audioOutput->plugin->send_tag(audioOutput, tag);
+		return;
+
+	audioOutput->args.tag = tag;
+	ao_command(audioOutput, AO_COMMAND_SEND_TAG);
 }

src/output_init.c

@@ -98,6 +98,10 @@ int audio_output_init(struct audio_output *ao, ConfigParam * param)
 	} else
 		audio_format_clear(&ao->reqAudioFormat);
 
+	ao->thread = 0;
+	notify_init(&ao->notify);
+	ao->command = AO_COMMAND_NONE;
+
 	if (plugin->init(ao, param) != 0)
 		return 0;
 

src/output_thread.c

@@ -0,0 +1,121 @@
+/* the Music Player Daemon (MPD)
+ * Copyright (C) 2008 Max Kellermann <max@duempel.org>
+ * This project's homepage is: http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include "output_thread.h"
+#include "output_api.h"
+#include "utils.h"
+
+static void ao_command_finished(struct audio_output *ao)
+{
+	assert(ao->command != AO_COMMAND_NONE);
+	ao->command = AO_COMMAND_NONE;
+	notify_signal(&audio_output_client_notify);
+}
+
+static void convertAudioFormat(struct audio_output *audioOutput,
+			       const char **chunkArgPtr, size_t *sizeArgPtr)
+{
+	size_t size = pcm_sizeOfConvBuffer(&(audioOutput->inAudioFormat),
+					   *sizeArgPtr,
+					   &(audioOutput->outAudioFormat));
+
+	if (size > audioOutput->convBufferLen) {
+		if (audioOutput->convBuffer != NULL)
+			free(audioOutput->convBuffer);
+		audioOutput->convBuffer = xmalloc(size);
+		audioOutput->convBufferLen = size;
+	}
+
+	*sizeArgPtr = pcm_convertAudioFormat(&(audioOutput->inAudioFormat), 
+	                                     *chunkArgPtr, *sizeArgPtr, 
+	                                     &(audioOutput->outAudioFormat),
+	                                     audioOutput->convBuffer,
+	                                     &audioOutput->convState);
+
+	*chunkArgPtr = audioOutput->convBuffer;
+}
+
+static void ao_play(struct audio_output *ao)
+{
+	const char *data = ao->args.play.data;
+	size_t size = ao->args.play.size;
+
+	if (!audio_format_equals(&ao->inAudioFormat, &ao->outAudioFormat))
+		convertAudioFormat(ao, &data, &size);
+
+	ao->result = ao->plugin->play(ao, data, size);
+	ao_command_finished(ao);
+}
+
+static void *audio_output_task(void *arg)
+{
+	struct audio_output *ao = arg;
+
+	notify_enter(&ao->notify);
+
+	while (1) {
+		switch (ao->command) {
+		case AO_COMMAND_NONE:
+			break;
+
+		case AO_COMMAND_OPEN:
+			assert(!ao->open);
+			ao->plugin->open(ao);
+			ao_command_finished(ao);
+			break;
+
+		case AO_COMMAND_CLOSE:
+			assert(ao->open);
+			ao->plugin->close(ao);
+			ao_command_finished(ao);
+			break;
+
+		case AO_COMMAND_PLAY:
+			ao_play(ao);
+			break;
+
+		case AO_COMMAND_CANCEL:
+			ao->plugin->cancel(ao);
+			ao_command_finished(ao);
+			break;
+
+		case AO_COMMAND_SEND_TAG:
+			ao->plugin->send_tag(ao, ao->args.tag);
+			ao_command_finished(ao);
+			break;
+
+		case AO_COMMAND_KILL:
+			ao_command_finished(ao);
+			return NULL;
+		}
+
+		notify_wait(&ao->notify);
+	}
+}
+
+void audio_output_thread_start(struct audio_output *ao)
+{
+	pthread_attr_t attr;
+
+	assert(ao->command == AO_COMMAND_NONE);
+
+	pthread_attr_init(&attr);
+	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+	if (pthread_create(&ao->thread, &attr, audio_output_task, ao))
+		FATAL("Failed to spawn output task: %s\n", strerror(errno));
+}

src/output_thread.h

@@ -0,0 +1,26 @@
+/* the Music Player Daemon (MPD)
+ * Copyright (C) 2008 Max Kellermann <max@duempel.org>
+ * This project's homepage is: http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#ifndef OUTPUT_THREAD_H
+#define OUTPUT_THREAD_H
+
+struct audio_output;
+
+void audio_output_thread_start(struct audio_output *ao);
+
+#endif