At Mon, 2 Feb 2009 15:49:13 +0100, Lennart Poettering wrote: > > On Mon, 02.02.09 08:02, Takashi Iwai (tiwai@xxxxxxx) wrote: > > > > If we look into the pcm example how snd_pcm_poll_descriptors_revents() > > > is used then we can see that the revents parameter apparently is > > > supposed to be a single integer. (which makes a lot of sense to me) > > > > > > http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html#a33 > > > > > > However, snd_pcm_wait_nocheck() calls the same function and assumes it > > > is a complete array! > > > > > > http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/pcm/pcm.c;h=74d1d1a4bd6083cd461b6d793c0ae41cca912f16;hb=HEAD#l2368 > > > > > > So what's it now? It makes more sense to me if it would be a single > > > fd. > > > > No, it's a bug in test/pcm.c. As documented, the API converts (fixes) > > each poll_fd in the given array. > > But does that really make sense? I mean > snd_pcm_poll_descriptors_revents() is supposed to be called by > applications that integrate ALSA into some kind of event loop. What > are they supposed to do with those multiple entries -- except simply > ORing them together and treating them as one? The application has no > information what those seperate fds mean, so why export that > information to the app? Originally the multiple pfds were introduced to handle multi plugin, which bundles multiple instances. So, the original version of it was pretty straightforward -- just simply calls poll to each and update each pfd necessarily. After some time, multi plugin itself was changed to expose only a single pfd, so there is no meaning for that. That's why it never got a realistic problem. Meanwhile, hw pcm introduced the multiple pfds again (for cases with timer), and this could be a problem again right now. It's not about the question whether it makes sense. It *was* designed so originally although it's fairly useless. Due to the uselessness, one side got fixed, but another side remained. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
