From mboxrd@z Thu Jan  1 00:00:00 1970
From: James Courtier-Dutton <James@superbug.demon.co.uk>
Subject: Re: problems using select() on alsa pcm.
Date: Thu, 25 Mar 2004 15:13:34 +0000
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References: <200403250408.i2P48qDC021625@dhin.linuxaudiosystems.com> <Pine.LNX.4.58.0403251037200.1807@pnote.perex-int.cz>
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To: Jaroslav Kysela <perex@suse.cz>
Cc: Paul Davis <paul@linuxaudiosystems.com>, alsa-devel <alsa-devel@lists.sourceforge.net>
List-Id: alsa-devel@alsa-project.org

Jaroslav Kysela wrote:
> On Wed, 24 Mar 2004, Paul Davis wrote:
> 
> 
>>>open pcm, and get a handle.
>>>
>>>snd_pcm_poll_descriptors(handle, &pfd, err);
>>>
>>>Get a poll file scriptor in pfd.
>>>
>>>select(nfds, rfds, wfds, efds, tvp);
>>>
>>>Is it possible to use this call with alsa ?
>>
>>select is generally deprecated in linux (linus says so!). but you can
>>use the same pfds in select as in poll (select is implemented in the
>>kernel using the poll code). the problem is interpreting the results
>>you get back (as noted recently for the dmix plugin).
> 
> 
> Nope, the application must give results back to pfd array and call
> snd_pcm_poll_descriptors_revents() function. In this way, everything
> will work as expected.
> 
> 						Jaroslav
So which of the following is needed: -

snd_pcm_poll_descriptors(handle, &pfd, err);
select(nfds, rfds, wfds, efds, tvp);
snd_pcm_poll_descriptors_revents()  <- decode the results of the select.

or
snd_pcm_poll_descriptors(handle, &pfd, err);
snd_pcm_poll_descriptors_revents()  <- rearrange the pfd so that select 
works as expected.
select(nfds, rfds, wfds, efds, tvp);

Cheers
James


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