pcm write from posix threads

pcm write from posix threads

[Brian Rhodes]

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.

Re: pcm write from posix threads

[Takashi Iwai]

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

Re: pcm write from posix threads

[Brian Rhodes]

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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