[vlc-devel] [PATCH] decoder: fix occasional deadlock on seek

[Thomas Guillem]

On Mon, Oct 9, 2017, at 22:25, Rémi Denis-Courmont wrote:
> Le maanantaina 9. lokakuuta 2017, 18.06.46 EEST Thomas Guillem a écrit :
> > This commit fixes the following deadlock:
> > 
> > The input thread (from input_DecoderWait()) reads p_owner->b_idle, and wait
> > on the wait_acknowledge condition variable because p_owner->b_idle is false
> > (and because p_owner->b_has_data is false too). The decoder thread sets
> > p_owner->b_idle to true because the fifo is empty and wait on the fifo
> > condition variable. Both threads are waiting each others, hence the
> > deadlock.
> > 
> > To fix this issue, signal the input thread from the decoder thread after
> > setting p_owner->b_idle to true.
> > 
> > Since predictable scheduling behavior is not required, p_owner->lock doesn't
> > have to be held while signaling p_owner->wait_acknowledge.
> > 
> > Fixes #16100
> 
> I don't know if this is right or wrong. Or rather, I know that the
> current 
> buffering algorithm is fundamentally flawed regardless of this patch. So
> I 
> find it impossible to reason about.

We'll fix one the buffering algorith but not today, not for 3.0.
This is more an hack on top of an existing hack but this really fix the
last deadlock that I often see(I hope).

Having 2 different mutexes in this part of the code make the things
really more complex to me. I'll try to merge them, don't know if it can
be merged for 3.0.

> 
> -- 
> Rémi
> https://www.remlab.net/
> 
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