On Thu, 2010-06-03 at 15:40 +0100, James Courtier-Dutton wrote: > On 2 June 2010 22:29, John Lindgren <john.lindgren@xxxxxxx> wrote: > > Hi, > > > > In a multi-threaded application it is possible for snd_pcm_delay or an > > equivalent function to be called by one thread while another is sitting > > in snd_pcm_writei. In this case, snd_pcm_delay does not take into > > account that there may not be enough space for all the data passed to > > snd_pcm_writei to be written to the ring buffer at once, and will return > > incorrect values. > > I believe the definition of snd_pcm_delay() is it returns a value that > would be fairly accurate at this instance of time. If you followed the > snd_pcm_delay() with a snd_pcm_writei(), the samples would reach the > speaker "delay" time later. > > I think it would be fair to say that the value of snd_pcm_delay() is > undefined if called during a snd_pcm_writei() call, because you will > get a return value from snd_pcm_delay() but you will have no idea how > many samples of the current snd_pcm_writei() have been written and > thus no idea what the delay will be on the next snd_pcm_writei(). > > Even in multi-threaded applications calling two functions at the same > time that interfere with each other it not good. > If a function is re-entrant it is generally considered to be thread > safe. It does not necessarily mean that it is sensible to call two > different functions at the same time. I understand that snd_pcm_delay and snd_pcm_writei currently "interfere with each other" in that snd_pcm_delay returns wrong values if called during snd_pcm_writei. That is the problem my patch tries to correct. Do you disagree with this improvement? If so, why? John Lindgren _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
