On Wed, 17 Aug 2016 19:46:42 +0200, Jaroslav Kysela wrote: > > Dne 16.8.2016 v 23:03 Samuel Thibault napsal(a): > > Hello, > > > > We are having odd issues with libasound 1.1.2 which we didn't have with > > libasound 1.1.1, more precisely > > > > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=833950 > > > > so I'm having a look at the locking API introduced in 1.1.2, and there > > are some oddities: > > > > - snd_pcm_new seems to initialize pcm->thread_safe to 0 by default, this > > does not seem safe. The attached patch initializes it to 1, which > > fixes the bug in our tests. > > > > - snd_pcm_hw_open_fd forces it to 1, thus ignoring what snd_pcm_new set. > > The thread_safe has this meaning: > > 0 - the pcm plugin is not thread safe > 1 - the pcm plugin is thread safe (actually only the hw plugin) > -1 - disable thread safety > > Your patch does not look correct. It's necessary to determine where the > mutex is locked the second time (use gdb and backtrace for all threads > for that). Note that plugins may be chained. > > > - one can find both __snd_pcm_lock and snd_pcm_lock functions, what is > > the expected difference between them? > > __snd_pcm_lock/unlock is for forced lock > > snd_pcm_lock/unlock skips locking for safe plugins (only hw plugin) > > > - __snd_pcm_lock takes locks when thread_safe >= 0, while snd_pcm_lock > > takes locks when thread_safe == 0, this looks really odd. > > See meaning of this variable. Thanks Jaroslav for explaining details! > > - libasound could just not link against libpthread, > > pthread_mutex_lock/unlock are already provided as empty stubs by libc, > > the overhead will thus only be hit when the application links against > > libpthread (libasound will then properly use pthread locks). > > Good point, but this should be configurable through the configure script. The thread-safety lock API usage is enabled only when pthread is enabled in configure script. So the least check in the configure script is already there. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
