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authorMax Kellermann <max@duempel.org>2009-03-11 09:35:16 +0100
committerMax Kellermann <max@duempel.org>2009-03-11 09:35:16 +0100
commitbc3702a4fd9237205df9316b21ea45917145a5f4 (patch)
treebcfe6a5fddbc8e78fd7bf007d58fa85269bca18b
parent13cd6b28348d2b744a01bea03c4764860f31f909 (diff)
downloadmpd-bc3702a4fd9237205df9316b21ea45917145a5f4.tar.gz
mpd-bc3702a4fd9237205df9316b21ea45917145a5f4.tar.xz
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player_thread: added comments
Diffstat (limited to '')
-rw-r--r--src/player_thread.c90
-rw-r--r--src/player_thread.h23
2 files changed, 89 insertions, 24 deletions
diff --git a/src/player_thread.c b/src/player_thread.c
index e1e2b21a7..07ad8bb61 100644
--- a/src/player_thread.c
+++ b/src/player_thread.c
@@ -1,6 +1,6 @@
-/* the Music Player Daemon (MPD)
- * Copyright (C) 2003-2007 by Warren Dukes (warren.dukes@gmail.com)
- * This project's homepage is: http://www.musicpd.org
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * 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
@@ -110,12 +110,17 @@ static void player_command_finished(void)
notify_signal(&main_notify);
}
+/**
+ * Stop the decoder and clears (and frees) its music pipe.
+ */
static void
player_dc_stop(struct player *player)
{
dc_stop(&pc.notify);
if (dc.pipe != NULL) {
+ /* clear and free the decoder pipe */
+
music_pipe_clear(dc.pipe, player_buffer);
if (dc.pipe != player->pipe)
@@ -125,6 +130,11 @@ player_dc_stop(struct player *player)
}
}
+/**
+ * After the decoder has been started asynchronously, wait for the
+ * "START" command to finish. The decoder may not be initialized yet,
+ * i.e. there is no audio_format information yet.
+ */
static bool
player_wait_for_decoder(struct player *player)
{
@@ -148,6 +158,9 @@ player_wait_for_decoder(struct player *player)
pc.next_song = NULL;
pc.elapsed_time = 0;
player->queued = false;
+
+ /* set the "starting" flag, which will be cleared by
+ player_check_decoder_startup() */
player->decoder_starting = true;
/* call syncPlaylistWithQueue() in the main thread */
@@ -156,6 +169,11 @@ player_wait_for_decoder(struct player *player)
return true;
}
+/**
+ * The decoder has acknowledged the "START" command (see
+ * player_wait_for_decoder()). This function checks if the decoder
+ * initialization has completed yet.
+ */
static bool
player_check_decoder_startup(struct player *player)
{
@@ -252,6 +270,9 @@ player_send_silence(struct player *player)
return true;
}
+/**
+ * This is the handler for the #PLAYER_COMMAND_SEEK command.
+ */
static bool player_seek_decoder(struct player *player)
{
double where;
@@ -260,14 +281,21 @@ static bool player_seek_decoder(struct player *player)
assert(pc.next_song != NULL);
if (decoder_current_song() != pc.next_song) {
+ /* the decoder is already decoding the "next" song -
+ stop it and start the previous song again */
+
player_dc_stop(player);
+ /* clear music chunks which might still reside in the
+ pipe */
music_pipe_clear(player->pipe, player_buffer);
dc.pipe = player->pipe;
- dc_start_async(pc.next_song);
+ /* re-start the decoder */
+ dc_start_async(pc.next_song);
ret = player_wait_for_decoder(player);
if (!ret) {
+ /* decoder failure */
player_command_finished();
return false;
}
@@ -276,6 +304,8 @@ static bool player_seek_decoder(struct player *player)
player->queued = false;
}
+ /* send the SEEK command */
+
where = pc.seek_where;
if (where > pc.total_time)
where = pc.total_time - 0.1;
@@ -284,6 +314,7 @@ static bool player_seek_decoder(struct player *player)
ret = dc_seek(&pc.notify, where);
if (!ret) {
+ /* decoder failure */
player_command_finished();
return false;
}
@@ -331,8 +362,11 @@ static void player_process_command(struct player *player)
pc.state = PLAYER_STATE_PLAY;
} else if (audio_output_all_open(&player->play_audio_format, player_buffer)) {
+ /* unpaused, continue playing */
pc.state = PLAYER_STATE_PLAY;
} else {
+ /* the audio device has failed - rollback to
+ pause mode */
assert(dc.next_song == NULL || dc.next_song->url != NULL);
pc.errored_song = dc.next_song;
pc.error = PLAYER_ERROR_AUDIO;
@@ -349,7 +383,7 @@ static void player_process_command(struct player *player)
case PLAYER_COMMAND_CANCEL:
if (pc.next_song == NULL) {
- /* the cancel request arrived too later, we're
+ /* the cancel request arrived too late, we're
already playing the queued song... stop
everything now */
pc.command = PLAYER_COMMAND_STOP;
@@ -368,6 +402,11 @@ static void player_process_command(struct player *player)
}
}
+/**
+ * Plays a #music_chunk object (after applying software volume). If
+ * it contains a (stream) tag, copy it to the current song, so MPD's
+ * playlist reflects the new stream tag.
+ */
static bool
play_chunk(struct song *song, struct music_chunk *chunk,
const struct audio_format *format, double sizeToTime)
@@ -399,6 +438,8 @@ play_chunk(struct song *song, struct music_chunk *chunk,
}
}
+ /* apply software volume */
+
success = pcm_volume(chunk->data, chunk->length,
format, pc.software_volume);
if (!success) {
@@ -409,6 +450,8 @@ play_chunk(struct song *song, struct music_chunk *chunk,
return false;
}
+ /* send the chunk to the audio outputs */
+
if (!audio_output_all_play(chunk)) {
pc.errored_song = dc.current_song;
pc.error = PLAYER_ERROR_AUDIO;
@@ -433,8 +476,8 @@ play_next_chunk(struct player *player)
bool success;
if (audio_output_all_check() >= 64) {
- /* the output pipe is still large
- enough, don't send another chunk */
+ /* the output pipe is still large enough, don't send
+ another chunk */
/* XXX synchronize in a better way */
g_usleep(1000);
@@ -450,11 +493,10 @@ play_next_chunk(struct player *player)
music_pipe_shift(dc.pipe);
if (!player->cross_fading) {
- /* beginning of the cross fade
- - adjust crossFadeChunks
- which might be bigger than
- the remaining number of
- chunks in the old song */
+ /* beginning of the cross fade - adjust
+ crossFadeChunks which might be bigger than
+ the remaining number of chunks in the old
+ song */
player->cross_fade_chunks = cross_fade_position;
player->cross_fading = true;
}
@@ -469,16 +511,13 @@ play_next_chunk(struct player *player)
player->cross_fade_chunks);
music_buffer_return(player_buffer, other_chunk);
} else {
- /* there are not enough
- decoded chunks yet */
+ /* there are not enough decoded chunks yet */
if (decoder_is_idle()) {
- /* the decoder isn't
- running, abort
+ /* the decoder isn't running, abort
cross fading */
player->xfade = XFADE_DISABLED;
} else {
- /* wait for the
- decoder */
+ /* wait for the decoder */
notify_signal(&dc.notify);
notify_wait(&pc.notify);
@@ -502,9 +541,8 @@ play_next_chunk(struct player *player)
return false;
}
- /* this formula should prevent that the
- decoder gets woken up with each chunk; it
- is more efficient to make it decode a
+ /* this formula should prevent that the decoder gets woken up
+ with each chunk; it is more efficient to make it decode a
larger block at a time */
if (!decoder_is_idle() &&
music_pipe_size(dc.pipe) <= (pc.buffered_before_play +
@@ -535,6 +573,11 @@ player_song_border(struct player *player)
return true;
}
+/*
+ * The main loop of the player thread, during playback. This is
+ * basically a state machine, which multiplexes data between the
+ * decoder thread and the output threads.
+ */
static void do_play(void)
{
struct player player = {
@@ -576,6 +619,10 @@ static void do_play(void)
}
if (player.buffering) {
+ /* buffering at the start of the song - wait
+ until the buffer is large enough, to
+ prevent stuttering on slow machines */
+
if (music_pipe_size(player.pipe) < pc.buffered_before_play &&
!decoder_is_idle()) {
/* not enough decoded buffer space yet */
@@ -595,6 +642,7 @@ static void do_play(void)
}
if (player.decoder_starting) {
+ /* wait until the decoder is initialized completely */
bool success;
success = player_check_decoder_startup(&player);
diff --git a/src/player_thread.h b/src/player_thread.h
index f8b88f65d..6fd62ec7e 100644
--- a/src/player_thread.h
+++ b/src/player_thread.h
@@ -1,6 +1,6 @@
-/* the Music Player Daemon (MPD)
- * Copyright (C) 2008 Max Kellermann <max@duempel.org>
- * This project's homepage is: http://www.musicpd.org
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * 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
@@ -16,6 +16,23 @@
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
+/* \file
+ *
+ * The player thread controls the playback. It acts as a bridge
+ * between the decoder thread and the output thread(s): it receives
+ * #music_chunk objects from the decoder, optionally mixes them
+ * (cross-fading), applies software volume, and sends them to the
+ * audio outputs via audio_output_all_play().
+ *
+ * It is controlled by the main thread (the playlist code), see
+ * player_control.h. The playlist enqueues new songs into the player
+ * thread and sends it commands.
+ *
+ * The player thread itself does not do any I/O. It synchronizes with
+ * other threads via #GMutex and #GCond objects, and passes
+ * #music_chunk instances around in #music_pipe objects.
+ */
+
#ifndef MPD_PLAYER_THREAD_H
#define MPD_PLAYER_THREAD_H