Re: Re: [Jackit-devel] alsa_driver_wait -> libasound?

[Takashi Iwai <tiwai@suse.de>]

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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