At Tue, 14 Jan 2003 09:38:51 -0500,
Paul Davis wrote:
>
>
> [ cc'ed to alsa-devel ]
>
> >I think I've asked something to this effect before, but is there any
> >reason why the polling portion of alsa_driver_wait should not be in
> >libasound? It's a very complicated piece of code that performs an
> >operation that many programs are likely to want. What if it was written
> >as a companion function to snd_pcm_wait():
> >
> > int snd_pcm_wait_many( snd_pcm_t **handles, int num_handles,
> > int timeout);
> >
> >...not that JACK would have to give up its version with extra error
> >reporting and timing, but for programs with simpler needs it would be a
> >lot nicer than having to set and test all those poll conditions for all
> >of the pfds on all the handles.
> >
> >I should probably ask this on the ALSA list, but I'm more familiar with
> >the people here. Any reason why this couldn't go into libasound?
>
> seems like a good idea to me, although there is a small problem. the
> current snd_pcm_wait function waits till the handles is
> readable/writable, whereas the JACK code waits till the handles all
> have a certain minimum amount of data/space. this is a subtle but
> rather important difference.
i thought that snd_pcm_wait() waits until data/space of
swparams->avail_min become available, too?
>
> that said, i think it would be great if this found its way into libasound.
is the below code ok?
int snd_pcm_wait_many(snd_pcm_t **handles, int num_handles, int timeout)
{
struct pollfd *pfds;
int i, err;
pfds = (struct pollfd *)alloca(sizeof(*pfds) * num_handles);
if (! pfds)
reutrn -ENOMEM;
for (i = 0; i < num_handles; i++) {
err = snd_pcm_poll_descriptors(handles[i], &pfds[i], 1);
assert(err == 1);
}
err = poll(pfds, num_handles, timeout);
if (err < 0)
return -errno;
return err > 0 ? 1 : 0;
}
Takashi
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