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/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));
+}