[LAU] JACK hanging upon slight USB power glitch

[Jeremy Jongepier]

On 14-10-13 05:04, James Harkins wrote:
> Sorry if this is an obvious question, but I'm short of time today and
> really tired of Google searching.
> 
> I'm running:
> 
> Linux dlm-A6200 3.2.0-54-lowlatency #56-Ubuntu SMP PREEMPT Thu Sep 19
> 17:22:47 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
> 
> I have jack 2 connected via ALSA to an M-Audio Fast Track Pro.
> 
> If there is any slight glitch in the USB power -- for instance, in a
> performance space where the sound engineer might need to plug/unplug
> cables frequently -- jackd spins out of control on one CPU and often
> locks up the user interface, forcing a hard shutdown and reboot. If I'm
> very lucky, I can get into the terminal, find jack's PID and kill it,
> but when the mouse and keyboard stop responding, there's nothing I can
> do reach for the power button.
> 

Hello James,

This doesn't work either to reboot?
http://en.wikipedia.org/wiki/Magic_SysRq_key#Uses

> This occurs less frequently in 12.04 than it did when I started with
> 10.04, but when it does happen (as it did just now), it really, really
> ticks me off.
> 
> I think there must be some automated way for the system to recognize
> that jack is out of control and kill it. [1] notes:
> 
>       -t, --timeout int
>              Set client timeout limit in milliseconds.  The  default 
> is  500
>              msec.   In realtime mode the client timeout must be smaller
> than
>              the watchdog timeout (5000 msec).
> 
> Interesting... "watchdog timeout"... but I have never seen any effect
> from the watchdog mentioned here. Jack just keeps locking up the system
> for way longer than 5 seconds.
> 

Afaik Jack2 doesn't have a watchdog thread.

> I'm happy to provide more info if you can tell me what commands to run.
> Normally I would research it myself, but I'm just not in the mood today.
> If there's already good documentation on this, great, but... too many
> pages to read and I have no idea which is the best one.
> 

Maybe you could try with a split USB cable:
http://sourceforge.net/apps/mediawiki/guitarix/index.php?title=Guitarix_Embedded_/_ARM_SoC#Fighting_the_Noise

Jack2 has D-Bus support so maybe you could do something creative with that.

Best,

Jeremy

> Thanks,
> hjh
> 
> [1] http://manpages.ubuntu.com/manpages/precise/man1/jackd.1.html
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