[alsa-devel] snd_pcm_drain and lockups

[Arve Knudsen]

On 9/6/07, Takashi Iwai <tiwai at suse.de> wrote:
>
> At Wed, 5 Sep 2007 19:19:10 +0200,
> Arve Knudsen wrote:
> >
> > Hi Takashi
> >
> > On 9/5/07, Takashi Iwai <tiwai at suse.de> wrote:
> > >
> > > At Tue, 4 Sep 2007 23:03:27 +0200,
> > > Arve Knudsen wrote:
> > > >
> > > > Hello
> > > >
> > > > Users of the PortAudio library on top of ALSA-lib have reported that
> it
> > > may
> > > > hang in a call to snd_pcm_drain. I have also been able to confirm
> that
> > > this
> > > > can happen in conjunction with the dmix device at least. Can the
> ALSA
> > > > developers please tell me how, if at all, snd_pcm_drain may be
> safely
> > > used?
> > > > Is this function simply best avoided (snd_pcm_drop being the
> > > alternative)?
> > >
> > > Of course, it's supposed to be safe to use :)  But, it's hard to tell
> > > you more unless I get the details in your case...
> > >
> > > In which situation is it called?  Are they multi-threaded?
> >
> >
> > The lock-up happens in a background thread within PortAudio. What has
> been
> > known to cause lock-ups at least is that PA restarts the device after
> the
> > detection of an xrun. This procedure entails first draining the stream
> > (snd_pcm_drain), the dmix and front devices have been known to lock up
> here
> > (I've experienced it with dmix at least). I've googled a bit on the
> problem,
> > and I didn't find a whole lot of evidence of this problem, but I did
> find
> > this:
> http://www.ohloh.net/projects/5344/contributors/32264/commits/10293341
> > .
>
> It's still hard to imagine what's going on there without a small test
> case.  I vaguely remember a similar problem, but I thought it should
> have been fixed in the recent versions.


I can try to procure a test case, but I believe it happens rather randomly.

Arve