[Jack-Devel] [PATCH] Don't start pcm if its already RUNNING - JackAudio

1 Jul 2015

A few months ago we'd digged jackd code in #alsa IRC trying to find why itfails with
"ALSA: could not start playback (File descriptor in bad state)"when run on top
"type bluetooth" pcm. The reason was in a single line (both in
jack1/drivers/alsa/alsa_driver.cand jack2/linux/alsa/alsa_driver.c):&nbsp; if ((err =
snd_pcm_start (driver-&gt;playback_handle)) &lt; 0) {which always fails after
snd_pcm_mmap_commit() filling the buffer,because pcm's already in RUNNING state and
can't be started again:&gt;
http://www.alsa-project.org/alsa-doc/alsa-lib/pcm.html&gt; For playback, if samples in
ring buffer is equal or greater than&gt; the start threshold parameters and the stream
is not running,&gt; the stream will be started automaticallyThe following small patch
fixes it for both jack1 and jack2:--- alsa_driver.c+++
alsa_driver.c&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;@@ -1055,7
+1055,8 @@ alsa_driver_start (alsa_driver_t
*driver&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
driver-&gt;user_nperiods&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
*
driver-&gt;frames_per_cycle);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
&nbsp;-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
if ((err = snd_pcm_start (driver-&gt;playback_handle)) &lt; 0)
{+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
if (snd_pcm_state(driver-&gt;playback_handle) !=
SND_PCM_STATE_RUNNING+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
&amp;&amp; (err = snd_pcm_start (driver-&gt;playback_handle)) &lt; 0)
{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
jack_error ("ALSA: could not start playback
(%s)",&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
snd_strerror
(err));&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
return -1;