Re: Re: quit snd_pcm_readi, retrieve pending frames

[Gerald Grabner <gerald.grabner@gmx.net>]

Takashi Iwai wrote:
> At Fri, 19 May 2006 21:17:45 +0000 (UTC),
> Gerald Grabner wrote:
>> Takashi Iwai <tiwai <at> suse.de> writes:
>>> At Mon, 15 May 2006 12:06:47 +0200,
>>> I wrote:
>>>> At Sat, 13 May 2006 13:06:51 +0200,
>>>> Gerald Grabner wrote:
>>>>> Hi,
>>>>>
>>>>> I'm experimenting with the ALSA PCM API and was wondering whether
>>>>> there is a simple way to exit a record loop by stopping the pcm, but
>>>>> without loosing pending frames.
>>>>>
>>>>> Initially, I was thinking of something like this, where I would call
>>>>> snd_pcm_drop(pcm) from some other thread:
>>>>>
>>>>>    while ( true )
>>>>>      {
>>>>>        r = snd_pcm_readi (pcm, data, frames);
>>>>>        fwrite (data, 2, 2*r, file);
>>>>>        if ( r != frames )
>>>>>          break;
>>>>>      }
>>>>>
>>>>> However, snd_pcm_drain(pcm) doesn't work here; the loop continues.
>>>>> snd_pcm_drop(pcm) breaks the loop, but pending frames are lost, and
>>>>> r=-EBADFD.
>>>>>
>>>>> Is there an easy way to stop snd_pcm_readi in a way that I can
>>>>> retrieve the residual frames? Do I need to set any parameters for
>>>>> that purpose?
>>>> If you're using hw or plughw, it's likely a bug in alsa-driver.
>>>> Try the patch below.
>>> Actually the patch was also wrong.  snd_pcm_drain() shouldn't wait for
>>> the capture streams.  So, the patch becomes pretty simple like below.
>>> I'll commit it to HG repo.
>>>
>>> Takashi
>>>
>>> diff -r 44d28ed5d3d5 core/pcm_native.c
>>> --- a/core/pcm_native.c	Wed May 17 11:26:39 2006 +0200
>>> +++ b/core/pcm_native.c	Wed May 17 17:07:17 2006 +0200
>>>  <at>  <at>  -1469,8 +1469,6  <at>  <at>  static int snd_pcm_drain(
>> struct snd_pcm_
>>>  		}
>>>  	}
>>>  	up_read(&snd_pcm_link_rwsem);
>>> -	if (! num_drecs)
>>> -		goto _error;
>>>
>>>  	snd_pcm_stream_lock_irq(substream);
>>>  	/* resume pause */
>>
>> Hi Takashi,
>>
>> there seems to be some problem with this patch (the short one). After
>> recompiling the kernel (and my application), my application doesn't
>> exit and I can't kill it anymore. The pcm device is kind of lost. See
>> below for the /var/log/messages entry.
> 
> Hmm, according the error message below, I suspect it's something
> different since the patch isn't so intrusive.
> 
> Could you test again after reverting the patched part?

After recompiling the kernel with the original source, the problem
disappeared.

Gerald


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