[alsa-devel] [Pkg-alsa-devel] Bug#438118: alsa-utils: aplay non-blocking mode isn't working

[Takashi Iwai]

At Thu, 27 Sep 2007 14:16:29 +0200 (CEST),
Anders Boström wrote:
> 
> >>>>> "TI" == Takashi Iwai <tiwai at suse.de> writes:
> 
>  TI> At Tue, 18 Sep 2007 09:41:48 +0200 (CEST),
>  TI> Anders Boström wrote:
>  >> 
>  >> >>>>> "TI" == Takashi Iwai <tiwai at suse.de> writes:
>  >> 
>  >> >> can one please have a lokk at this? aplay -N isn't working for the
>  >> >> OP.
>  >> 
>  TI> Cannot reproduce here.  Could you _post_ more details?
>  >> 
>  >> OK, I've tested more, and discovered that the problem seems to be that
>  >> the end of the sound is cut in non-blocking mode. And if I play a very
>  >> short sound-file, I can't hear anything. Blocking mode works fine.
>  >> 
>  >> When using non-blocking mode, an strace contains "ioctl(4, 0x4144,
>  >> 0x2b9f785d8000)        = -1 EAGAIN (Resource temporarily
>  >> unavailable)". Blocking mode never contains the EAGAIN response.
>  >> 
>  >> I attach two files. When playing halt.au, I can only hear the start,
>  >> about as much as "ha". When playing metal.au, I can't hear anything.
> 
>  TI> OK, thanks, I see the problem now.
> 
>  TI> I don't remember whether it's a feature or a bug.  The drain ioctl
>  TI> rejects the non-block mode.
> 
> I can understand the idea here, that in non-blocking mode, no call
> should block, ever. But on the other hand, if you call the drain
> ioctl, you probably expect it to work, even in non-blocking mode. Why
> would you otherwise call it?

Yes, that's my opinion, too.  This particular ioctl is to block the
operation, so it should be allowed as long as it's called.

But I vaguely remember that we discussed about it, and the current
form is the result of that.  Namely, we can call
snd_pcm_nonblock(FALSE) explicitly before calling snd_pcm_drain().

Though, I prefer fixing the behavior in the core side to allow the
blocking with this call...  Any reasonable objections in mind?


Takashi