[Alsa-dev]detecing if a device is already used by an other app

[Alsa-dev]detecing if a device is already used by an other app

[Cournapeau David]

Hi there,

    I am currently using two computers which have a crappy intl8x0 audio 
chipset, and these chipset cannot be used by two different apps in the 
same time. For example, if an audio app is using the soundcard, trying 
to launch xmms ( with alsa output plugin) gives an error message which 
says something like "check that no other app is blocking the device". 
But if I launch alsaplayer (alsa output plugin) instead of xmms, the app 
doesn't complain: it 'just' blocks on the snd_pcm_open call.
    Basically, after having looked at the source, is seems like this 
difference is coming from the flag in snd_pcm_open: if SND_PCM_NONBLOCK  
is used, opening an already opened device failed, if SND_PCM_ASYNC is 
used, the app just blocks, until the other app releases the device.

    Is there a (simple) way to use the blocking call and detecting if 
the device is already opened ?

    Thank you,

    David


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Re: [Alsa-dev]detecing if a device is already used by an other app

[Måns Rullgård]

Cournapeau David <cournape@atr.jp> writes:

> Hi there,
>
>     I am currently using two computers which have a crappy intl8x0
>     audio chipset, and these chipset cannot be used by two different
>     apps in the same time. For example, if an audio app is using the
>     soundcard, trying to launch xmms ( with alsa output plugin) gives
>     an error message which says something like "check that no other
>     app is blocking the device". But if I launch alsaplayer (alsa
>     output plugin) instead of xmms, the app doesn't complain: it
>     'just' blocks on the snd_pcm_open call.
>     Basically, after having looked at the source, is seems like this
>     difference is coming from the flag in snd_pcm_open: if
>     SND_PCM_NONBLOCK  is used, opening an already opened device
>     failed, if SND_PCM_ASYNC is used, the app just blocks, until the
>     other app releases the device.

This is correct.

>     Is there a (simple) way to use the blocking call and detecting if
>     the device is already opened ?

You can open it in non-blocking mode and set it to blocking later, if
you want that behavior when writing data.

-- 
Måns Rullgård
mru@kth.se



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