Re: [Jack-Devel] Jack 0.120 incorrect error recovery for -n 3

On Mon, Apr 18, 2011 at 04:11:06PM +0200, torbenh wrote:
> On Sun, Apr 17, 2011 at 01:33:50PM +0000, Fons Adriaensen wrote:
> > On Sun, Apr 17, 2011 at 10:48:04AM +0000, Fons Adriaensen wrote:
> >  
> > > > So it randomly siwtches between 2 and 3 ?
> > > 
> > > It more or less alternates between the two, with
> > > some random element being involved as well.
> > > 
> > > As posted before, what happens is that after a
> > > subgraph timeout (which is reported) sometimes
> > > the alsa device is restarted (as it should be),
> > > and sometimes (when in the '-n 3' state) it
> > > isn't. Since in the same cycle there was no
> > > driver->write() (as the result of the timeout),
> > > things continue to work but with a period shift
> > > between playback and capture, as if '-n 2'. 
> > > When a new timeout occurs in that state it will
> > > trigger a stop/start, restoring the original
> > > conditions. So the net result is that the system
> > > almost alternates between the two states.
> > 
> > I found out a bit more.
> > 
> > 1. It seems the ALSA device restart is triggered by
> > an error condition in alsa_driver_wait() and not
> > by the engine.
> > 
> > 2. OTOH the engine, when there is subgraph timeout,
> > (in this case due to an app not closing down cleanly)
> > will not call driver->write() for the current cycle. 
> > 
> > With -n 3, (2) can happen without (1), as as far as
> > ALSA is concerned there is no problem - it still has
> > almost a complete period before anything overruns.
> > 
> > Now to keep things in sync either each cycle must be
> > completed fully, including writing to the ALSA device,
> > or the device must be restarted. This really should
> > be enforced 'by design' but it isn't.
> > 
> > There seem to be two solutions: 
> > 
> > A. Make sure the ALSA device is restarted when the
> > engine does not complete the cycle. This would 
> > negate any advantage there is to using -n 3, the
> > whole point of it is that an occasional single cycle
> > taking a bit too long is not fatal.
> > 
> > B. Always complete the cycle by calling driver-write().
> 
> B is the right thing to do, will look into it this evening.
> i dont remember, why i have changed this.

hmm... i actually did not change this.
i am still a bit puzzled, why this wasnt triggering before.

i committed (B) to svn.
its completely untested. please try it. and report back asap.
just doing a quick build test.

> 
> 
> > 
> > 
> > Ciao,
> > 
> > -- 
> > FA
> > 
> > 
> > 
> > 
> > 
> > 
> > Jack-Devel mailing list
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> > http://lists.jackaudio.org/listinfo.cgi/jack-devel-jackaudio.org
> 
> -- 
> torben Hohn
> 
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-- 
torben Hohn

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