On 10/22/2014 01:45 PM, Devin Heitmueller wrote: >> this seems like a feature, not a bug. PulseAudio starts streaming before >> clients push any data and likewise keeps sources active even after for some >> time after clients stop recording. Closing VLC in your example doesn't >> immediately close the ALSA device. look for module-suspend-on-idle in your >> default.pa config file. > > The ALSA userland emulation in PulseAudio is supposed to faithfully emulate > the behavior of the ALSA kernel ABI... except when it doesn't, then it's not > a bug but rather a feature. :-) > >> I also agree that the open/close of the alsa device is the only way to >> control exclusion. > > I was also a proponent that we should have fairly coarse locking done > at open/close for the various device nodes (ALSA/V4L/DVB). The challenge here > is that we have a large installed based of existing applications that > rely on kernel > behavior that isn't formally specified in any specification. Hence > we're forced to try > to come up with a solution that minimizes the risk of ABI breakage. > > If we were doing this from scratch then we could lay down some hard/fast rules > about things apps aren't supposed to do and how apps are supposed to respond > to those exception cases. Unfortunately we don't have that luxury here. > Sounds like we don't have a clear direction on open/close or capture start/stop. What I am hearing is open/close isn't acceptable for media maintainers and capture trigger start/stop isn't acceptable to sound maintainers. :) Fork in the road, which way do we go? Implementation wise, supporting capture trigger start/stop approach will be harder to maintain in longterm. It adds more variables to the mix. Applications open sounds device from the main thread and then create a new thread to handle streams. I can see that based on the token hold requests that come in. So the token hold logic will have to take that into account, leading into potential unbalanced lock/unlock scenarios. It is not impossible to solve, that's what I did in this patch series, but it does get complex. What I am looking for is some consensus on let's go with an approach and try. Doesn't matter which way we go, and how much testing I do, I am bound to miss something and this work needs to soak for a bit in the media experimental branch. thanks, -- Shuah -- Shuah Khan Sr. Linux Kernel Developer Samsung Research America (Silicon Valley) shuahkh@xxxxxxxxxxxxxxx | (970) 217-8978 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
