[pulseaudio-discuss] [PATCH] pulse: Fix invalid buffer pointer return value

[David Henningsson]

David Henningsson wrote:
>> 'Twas brillig, and David Henningsson at 09/01/10 09:00 did gyre and
>> gimble:
>>> The pulse ALSA plugin has been known, for a while, to not work properly,
>>> causing underruns, hangs etc. I sat down yesterday trying to figure it
>>> out, and I'm pretty certain this patch improves the situation, but I
>>> don't mind getting some help testing it before it is committed upstream.
>>>
>>> Related bug: https://bugs.launchpad.net/bugs/485488
>>>
>>> The patch is for the alsa-plugins tree at git.alsa-projects.org.
>> I applied this to 1.0.22 (cleanly) and sadly it's not helping my test
>> case using mpg123.
> 
> I've tried to debug the mpg123 issue a little further.

To sum up, I have two solutions/workarounds which both (independently)
fixes the mpg123 issue, but I could use some discussion regarding we
should apply either or both. And as said earlier, this is something
different from the patch posted earlier.

First, we can avoid the initial underrun altogether by avoiding calling
pa_stream_cork() and pa_stream_trigger() after having written just a few
bytes. If we do that, playback will start when prebuf number of bytes
have been written instead.

Second, we can ignore underruns if more buffers have been pushed since
the underrun occurred. Assuming the first fix is not applied, this will
cause an initial - to me inaudible - underrun, but since more buffers
are pushed in queue, the underrun will end automatically and after that
the stream will hopefully flow the way it should.

Both fixes can, at least in theory, cause regressions. (And according to
both Murphy's law and own experience - if it breaks in theory, it
probably breaks in practice as well!) The first fix could cause a
regression for short event sounds where we never reach the prebuf limit.
The second could perhaps cause regressions for ALSA clients
automatically increasing buffer size if they find an underrun. Hiding
that underrun would then be a bad thing.

// David