[alsa-devel] locking looks odd

[Alan Horstmann]

On Tuesday 30 August 2016 15:20, Takashi Iwai wrote:
> (Adding Alan to Cc)
>
> On Fri, 26 Aug 2016 21:02:12 +0200,
>
> Samuel Thibault wrote:
> > Samuel Thibault, on Sat 20 Aug 2016 14:12:05 +0200, wrote:
> > > I'd just like to check something: do we agree that libasound must be
> > > thread-safe by default (otherwise it breaks the application assumption
> > > that it's thread-safe)?  If so, then there are thread-safety bugs:
> >
> > Ok, now with the discussion on the portaudio list starting at
> >
> > https://lists.columbia.edu/pipermail/portaudio/2016-August/000599.html
> >
> > it seems the issue was in portaudio, which was hit by the locking
> > behavior change.
>
> Good to hear that it's been addressed in portaudio side.
>
> But I still wonder in which code path the deadlock was triggered.
> Can anyone give the stack traces of deadlocked (multi-)threads?

Actually, it wasn't so much the locking itself, but thread cancellation during 
one call (snd_pcm_mmap_commit()) leaving the lock held and not released, 
which then balked when a cleanup call to snd_pcm_drop() attempted to aquire 
the lock.  This occurred as a result of an 'Abort' action in Portaudio.  It 
can be avoided by disabling cancelablity at all times except when waiting on 
poll(), though I have yet to be completely satisfied  there are no snags in 
this approach, as cancelability is new to me!

Regards

Alan