[alsa-devel] pcm write from posix threads

Brian Rhodes bgr at acdstar.com
Wed Aug 20 10:39:18 CEST 2008

Thanks for reassuring me that there isn't some sort of incompatibility 
with alsa lib and threading.  I am not able to reproduce the issue on an 
x86 system and it only seems to happen when built with a specific 
toolchain for ARM.

Takashi Iwai wrote:
> At Tue, 19 Aug 2008 17:24:06 -0500,
> Brian Rhodes wrote:
>> When calling snd_pcm_write* from a thread how do you safely cancel the 
>> thread?  I've tried masking the signals which are used in alsa lib, yet 
>> I am getting a segfault on pthread_exit().  My thread is looping doing 
>> the following.
>> testcancel
>> snd_pcm_wait
>> snd_pcm_avail
>> snd_pcm_writei
>> I am checking return values to handle those functions being woken up by 
>> pthread cancel and attempting to exit.  In testing the process it 
>> performs fine until I start actually writing data.  Once I write some 
>> data, a pthread_exit will segfault.  My cancellation routine is calling 
>> snd_pcm_drop, then doing a cancel followed by join.
> No, alsa-lib functions don't care threads in general.
> Some codes have uses pthread_mutex, but not in the PCM core code, at
> least.
> You need to handle and protect threads by yourself.
> Takashi
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