[pulseaudio-discuss] [PATCH] alsa: Check respect return value of snd_pcm_mmap_commit()

[Alexander E. Patrakov]

12.11.2014 18:25, David Henningsson wrote:
>
>
> On 2014-11-12 14:15, Peter Meerwald wrote:
>> From: Peter Meerwald <p.meerwald at bct-electronic.com>
>>
>> snd_pcm_mmap_commit() actually transfers the memory area prepared by
>> snd_pcm_mmap_begin(),
>> it returns the 'count of transferred frames' which should be equal to
>> the number of frames
>> returned by snd_pcm_mmap_begin()
>>
>> however, this identify is not checked and the number of frames
>> prepared are accounted for,
>> not the number of frames commited -- this is wrong; the ALSA example
>> codes bothers to
>> check snd_pcm_mmap_commit()'s returned number of frames
>>
>> this patch outputs a warning and uses the commited number of frames to
>> update the bytes
>> read or written, resp.
>
> It's not that easy, I think...
>
> In case you get fewer frames written, you should retry the mmap_begin +
> mmap_commit cycle but *without* calling pa_sink_render_into_full, and
> only with the remaining frames. Right?

I'd question that. The alternative (but not something that I insist 
upon) is that pulseaudio should just sleep, as it would normally do 
according to its timer-based scheduling logic. Next time it wakes up, it 
should render some more frames (so that it has both old-unwritten and 
newly-rendered frames), and write (via mmap) as much as possible.

-- 
Alexander E. Patrakov