On 06-Mar-2004 Adam Tla/lka wrote: >> > On the Echoaudio cards the sample rate is a global setting, so I need a way >> > to prevent an app to change the rate if someone else already set it (the >> > card han several devices/subdevices). I was thinking to put a simple >> > "if (IsAudioOpen()) rate_min=rate_max=current_rate;" in pcm_open callback, >> > but this solution is racy.
> Talking about race conditions you could use a variable which is set to 0 > at the beginning. Now if app wants to set a rate it does atomic compare > and increase (cmpxchg on x86) instruction so only one app could set > rate. The other could only read memorized rate settins and report an > error if rate is different. No, I wasn't clear enough. If I add the "if (IsAudioOpen())..." in the pcm_open() function it works as long as the firts applications which set the sample rate don't changes it again. Furthermore, noone, but the firt app, can change the sample rate until all substream are closed. But there is another case where the above method fails. Let's suppose there are two application, A and B. They both do pcm_open(). Since nobody has set the sample rate yet, the driver says that all sample rates in the range 8k-96k can be choosed (the driver set hw constraints in the open callback). Then A sets 44100. But B still believes it can do 8-96 and it sets 48000. Everything goes fine until B tries to start the substream (that is the prepare() callback is called). At this point there are two possibilites: 1) The call fails and the application can't know why. 2) The call succeeds and it changes the sample rate of all running substreams. -- Giuliano. ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
