[vlc-devel] [V3 PATCH 3/3] dec: update pause/rate when the output is restarted

[Rémi Denis-Courmont]

Well it wouldn't surprise me if it created races or inversions. but it would surprise me if doing it one way would avoid races and the other way not.

Le 4 juillet 2018 11:37:57 GMT+03:00, Thomas Guillem <thomas at gllm.fr> a écrit :
>
>On Tue, Jul 3, 2018, at 17:58, Rémi Denis-Courmont wrote:
>> Le tiistaina 3. heinäkuuta 2018, 14.22.30 EEST Thomas Guillem a écrit
>:
>> > On Tue, Jul 3, 2018, at 13:20, Rémi Denis-Courmont wrote:
>> > > There should not be a need to move the current state out of the
>> > > stack, AFAIU.>
>> > > 
>> > >  I like to keep thread variables on stack because it's then
>obvious
>> > >  what the access rule is (read/write for the thread) and if the
>> > >  variable becomes unused.
>> > 
>> > Then, how do you fix what this commit is trying to fix ? With a
>reset
>> > bool that reset pause/rate from the DecoderThread stack ?
>> 
>> Set the correct values when you get the xout ?
>
>I implemented it (badly), pushed it, and force reverted it.
>It's more difficult than expected. With the 2 different locks and
>thread, it's hard (impossible?) to never miss a rate/paused state.
>
>I explain, cf. aout diff (the same for vout):
>
>@@ -384,6 +384,17 @@ static int aout_update_format( decoder_t *p_dec )
>             }
>         }
>
>+        vlc_fifo_Lock( p_owner->p_fifo );
>+        float rate = p_owner->rate;
>+        vlc_tick_t pause_date = p_owner->pause_date;
>+        bool paused = p_owner->paused;
>+        vlc_fifo_Unlock( p_owner->p_fifo );
>+
>+        if( paused )
>+            aout_DecChangePause( p_aout, paused, pause_date );
>+        if( rate != 1.f )
>+            aout_DecChangeRate( p_aout, rate );
>+
>         vlc_mutex_lock( &p_owner->lock );
>         p_owner->p_aout = p_aout;
>
>Here I update the aout state before writing it to p_owner->p_aout so
>that the DecoderThread won't change these states on its own. But if a
>new pause/rate is sent from the input between vlc_fifo_Unlock(
>p_owner->p_fifo ) and vlc_mutex_lock( &p_owner->lock ), and if the
>DecoderThread already process it in the meantime (and ignore it since
>since there is no aout), the state will be missed.
>
>
>Therefore, I prefer doing what this V3 patch set is doing.
>
>> 
>> -- 
>> Реми Дёни-Курмон
>> http://www.remlab.net/
>> 
>> 
>> 
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