Re: [Alsa-devel] problems using select() on alsa pcm.

[James Courtier-Dutton]

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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