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

[Takashi Iwai <tiwai@suse.de>]

At Tue, 14 Jan 2003 11:47:58 -0500,
Paul Davis wrote:
> 
> >> 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;
> >}
> 
> this isn't even close. the function in question waits until each and
> every handle is ready. that means reentering poll over and over again
> until each handle is ready, making sure to only poll on the handles
> that are not yet ready (because otherwise poll returns immediately).
> 
> the semantics are not "wait for any one many", its "wait for all or an
> error".
 
ah, now got the meaning.  so, something like that...

	// set up pfds...
	...
	for (;;) {
		err = poll(pfds, num_handles, timeout);
		if (err < 0)
			return -errno;
		else if (err == 0)
			return 0;
		i = 0;
		while (i < num_handles) {
			if (pfds[i].revents & POLLOUT) {
				num_handles--;
				memmove(pfds + i + 1, pfds + i,
					sizeof(*pfds) * (num_handles - i));
			} else
				i++;
		}
	}
	return 1;



Takashi


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