Re: streamdevice + asyn stuck

[Dirk Zimoch <dirk.zimoch@psi.ch>]

Hello Dehong,

Zhang, Dehong wrote:
> Hi Dirk and Mark,
>
> Thank you very much for helping!
>
> I tried to change the SCAN to "10 second", it did not help.  I also tried the
> epicsThreadShowAll command as Dirk suggested, it shows a few timerQueue
> threads, all "OK"

Some time ago I had the problem that I crashed the timerQueue thread in 
a timeout callback and thus never completed record processing. However, 
this seems to be a different issue because you don't see crashed threads.

> > From what I can see from the source code, I believe that we somehow
> lose callbacks from asyn, that breaks the evalcommand() chain and we
> never get to finishProtocol().

Yes. That seems to be the case. At several places, StreamDevice gives 
control to asyn or to EPICS base and relies on callbacks. If the 
callbacks don't come, StreamDevice is lost.

I have to check if I did anything wrong there. Basically I give control 
 to asynDriver using queueRequest() and expect a callback either to 
handleRequest() or handleTimeout(). From there I call the individual 
event handlers. So maybe either my queueRequest() setup is wrong or my 
handlers are buggy or asynDriver never calls back. (all code in 
AsynDriverInterface.cc)

Later I give control to EPICS base via callbackRequest() to finish 
processing the record. But I don't think that there is something wrong. 
(code in StreamEpics.cc)

I will try to add some diagnostics to see what a record is currently 
waiting for. But that may take a while.

> Another possibility is the mutex.  If it is not released properly, the
> Stream::process() method will be stuck waiting.

The mutex is automatically released (via destructor) when the function 
that contains the lock returns. Thus the only way to keep the lock is to 
get stuck in a function while holding the lock. But because I don't 
think I have unbounded loops in any function, that can only happen when 
a thread crashes or a function I call does not return. I don't think 
that happens.

Please switch on debugging (var streamDebug,1). Better remove or disable 
all other StreamDevice records or the output will be overwhelming. What 
are the last messages you get from a record before is gets stuck?


Dirk




> ________________________________________
> From: Dirk Zimoch [dirk.zimoch@psi.ch]
> Sent: Tuesday, July 12, 2011 12:21 AM
> To: Zhang, Dehong
> Cc: rivers@cars.uchicago.edu; tech-talk@aps.anl.gov
> Subject: Re: streamdevice + asyn stuck
>
> Hello Dehong,
>
> Do you have a hung up timerQueue thread? Try epicsThreadShowAll.
>
> Dirk
>
> Zhang, Dehong wrote:
> > Hi Dirk, Mark and fellow EPICSers,
> >
> > Sorry to bother you with this.  I tried to chase the source code and search the tech-talk,
> > but could not find much hints.
> >
> > We use base 3.14.9, streamdevice 2.4 and asyn 4.10, have been experiencing this stuck
> > problem for some time.  The symptom is that randomly, a mbbi/ai/bi... (input) record would
> > stop updating and no longer does FLNK, with no error/warning messages printed in the log
> > file.  And dbpr *** 3 would show that:
> > LCNT=11
> > SEVR=INVALID
> > STAT=SCAN
> >
> > And manually writing to the PROC field also does nothing.
> >
> > It seems like the record is stuck waiting for a callback from streamdevice (and asyn), and
> > the EPICS framework just ignores any "PROC" requests.
> >
> > In the protocol file we do have the timeouts etc:
> > locktimeout  = 5000;
> > terminator   = CR;
> > replytimeout = 1000;
> > readtimeout  = 1000;
> > extrainput   = Ignore;
> >
> > While chasing the problem, I noticed that "asynReport 10 ***" would show:
> > multiDevice:No canBlock:Yes autoConnect:Yes
> >     enabled:Yes connected:Yes numberConnects 1
> >
> > For some the numberConnects can be 2.
> >
> > Is this "canBlock:Yes" related to my problem?  Should the numberConnects be <=1?
> > We use one port to talk to one device.
> >
> > Rebooting the IOC does fix the problems, but then they would come back, randomly.
> >
> > Please advise.  Thank you very much.
> >
> > Best regards,
> > Dehong