[alsa-devel] Third time: Unlink PCM resource ?

Werner Van Belle werner at yellowcouch.org
Mon May 25 17:30:19 CEST 2009


This is the third time I tried to get information on the same topic but
there has been no response. Since it is crucial for me to get this to
work, I really would appreciate your input. If necssary I can provide
further documentation. The problem is as follows: if a process which
opened a DSP device forks of a new process, then this child will have
the same handle towards the DSP. What I now want to do is to release the
handle in the child without closing the device for the parent as well.
So essentially the sequence below illustrates the problem if one is
unable to 'unlink' a dsp device.

a- parent process creates and open dsp device
b- parent process forks of a child 1. Child 1 has access to the same dsp
c- parent process closes the DSP device
d- client process can no longer write to the DSP device (these are
already odd semantics, but okay, can live with it)
e- parent process forks of a second child. Child 2 has no dsp device
f- Child 2 tries to open the DSP device. This fails because the device,
although closed, is not released yet by Child 1.

Is this normal behavior ?
Is there some rigid documentation on the closing and sharing semantics
of pcm devices ?
Is there a way to unlink a device without closing it ?

If this is the wrong mailinglist, then who should I contact regarding
these erratic semantics ?


Dr. Werner Van Belle

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