Dne 16.3.2017 v 13:23 Max Kellermann napsal(a): > Hi, > > I have received a bug report for the Music Player Daemon which > complains about a freezing MPD process, after I switched MPD's ALSA > output to non-blocking mode: > > https://bugs.musicpd.org/view.php?id=4662 > > This happens when snd_pcm_drain() is used on a dmix PCM which is in > SND_PCM_NONBLOCK mode. snd_pcm_drain() will be called repeatedly, > because ALSA's file descriptor is always ready. > > According to my research, the bug is in __snd_pcm_dmix_drain(). This > function always returns -EAGAIN when SND_PCM_NONBLOCK is set: > > if (pcm->mode & SND_PCM_NONBLOCK) > return -EAGAIN; > > This comes very early in the function, before any other relevant > checks. It can never finish that way, and calling it again at any > time will never do anything. Thus, snd_pcm_drain() appears to be > broken in non-blocking mode. Could you test http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=fdc898d41135b26772d0fffe07e9eb0de6597125 ? There should be a loop with -EAGAIN, but this loop should end when then samples and drained. > Or am I misunderstanding how snd_pcm_drain() is supposed to be used in > non-blocking mode? For non-blocking mode, any calls won't block. So if you like to wait for the completion, you should do a poll/select call or switch the handle to the blocking mode. Jaroslav -- Jaroslav Kysela <perex@xxxxxxxx> Linux Sound Maintainer; ALSA Project; Red Hat, Inc. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
