On Sat, 20 Aug 2016 14:12:05 +0200, Samuel Thibault wrote: > > Jaroslav Kysela, on Wed 17 Aug 2016 19:46:42 +0200, wrote: > > Dne 16.8.2016 v 23:03 Samuel Thibault napsal(a): > > > - 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 > > So now with rethinking all of this, I'm starting to understand: from > reading the variable name, I would have thought "thread_safe=1" means > "I want thread safety thanks to a mutex", while apparently it means > "the plugin is already thread-safe, there is no need for a mutex"... > Really, all of this should be documented clearly along the source code, > otherwise people will get it wrong. Sorry for unclearness. An improvement patch is always welcome :) > I'd just like to check something: do we agree that libasound must be > thread-safe by default (otherwise it breaks the application assumption > that it's thread-safe)? If so, then there are thread-safety bugs: the > mentioned Debian report is far from alone, the upgrade to the newer > libasound has severely broken quite a few applications, I'm at the point > of advising the Debian maintainer to just revert to the previous version > for Stretch, otherwize we'll be shipping just very-buggy software. Basically the alsa-lib is not thread safe. The new thread-safe implementation was introduced just because there are way too many buggy applications that work casually for now. It's not meant as the rock-solid thread-safety alone. If the application deadlocks with the alsa-lib with the thread-safe option enabled, it's most likely that the application does already accessing alsa-lib in a wrong, racy way. In anyway, it'd be helpful to get stack trace of threads at the hanging moment. It'll clarify how the deadlock is triggered. The plugin may become a complex chain, and there might be something missing in the big picture. thanks, Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
