[pulseaudio-tickets] [Bug 54779] Live lock on daemon startup when module combine is used and real time scheduling is enabled

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https://bugs.freedesktop.org/show_bug.cgi?id=54779

--- Comment #6 from Tanu Kaskinen <tanuk at iki.fi> 2012-09-16 07:40:30 UTC ---
(In reply to comment #5)
> Created attachment 67041 [details] [review]
> Workaround for avoiding the live lock
> 
> So in pa_rtpoll_run timeout for ppoll is calculated with micro-second
> granularity and upscaled to nano-seconds for the actual ppoll call. 
> 
> Going deeper, time accounting is done via pa_rtclock_get and pa_timeval_cmp
> which internally downscale nano-seconds to micro-seconds.
> 
> This means if a sleep time is less than one micro-second, it will come out as
> zero in pa_rtpoll_run. This will make the RT thread busy loop and thread live
> lock on startup/shutdown.
> 
> This workaround patch works for me by ensuring no busy loop happens if time
> calculation did run and said zero sleep.
> 
> Real patch would I assume be to change the pa_rtclock API to work with timespec
> (nano-seconds) instead of timeval (micro-seconds). That way this down-scaling
> error would not happen.

Thanks for the patch, and especially for the debugging! Is it clear to you why
the rounding error causes the busy loop in the combine thread? I don't see why
that would happen.

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