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<== Date ==> <== Thread ==>

Subject: Re: Useless error messages in EPICS
From: "Martin L. Smith" <[email protected]>
To: Dirk Zimoch <[email protected]>
Cc: tech-talk <[email protected]>
Date: Mon, 02 Mar 2009 07:09:29 -0600
Hi Dirk,

I ran into this same problem back in January and it turns out that this
is Mantis entry 329. Jeff Hill made a fix for this; from a previous
email that I still have:

diff -u -b -w -b -r1.92.2.16 casStrmClient.cc
--- casStrmClient.cc 21 Oct 2008 20:50:26 -0000 1.92.2.16
+++ casStrmClient.cc 8 Jan 2009 22:13:09 -0000
@@ -1413,9 +1413,7 @@
this->chanTable.remove ( *pChan->pChanI );
this->chanList.remove ( *pChan->pChanI );
pChan->pChanI->uninstallFromPV ( this->eventSys );
- casPVI * pPVI = pChan->getPV()->pPVI;
delete pChan->pChanI;
- pPVI->deleteSignal ();
}

return status;

After Janet Anderson rebuilt the GW using this fix, which should be
committed to the repository, I have not had this problem since.

Marty

Dirk Zimoch wrote:
Hi all,

This night, I had a problem with a CA gateway. The log file contained the following error messages:

epicsMutex pthread_mutex_lock failed: error Invalid argument

Mar 02 00:04:46 !!! Errlog message received (message is above)
fatal error: epicsMutexOsdLock

Mar 02 00:04:46 !!! Errlog message received (message is above)

I found these messages not very helpful because they do not tell me where the error occurred and why the argument is invalid. This makes it impossible to debug the problem.

Unfortunately, this is often the case with EPICS errors. I observe three problems with locations of errors:

1. The error message does not give any hint of the location at all.

2. The reported location is inside a (EPICS) system function or a macro, but the caller who actually caused the error is not reported.

3. The reported location is inside the source code of a file parser but the error location in the faulty file is not reported.

In this case, we have situation 2. The problem occurred in epicsMutexOsdLock(), but this function is called at so many places in EPICS that it's impossible to track down the origin of the fault.

When looking into epicsMutexOsdLock(), I found that the calling thread is suspended via a call to cantProceed() when an error happens. In my opinion, this is as well not very helpful because the calling function does not get any indication of the failure and thus cannot print a proper error message.

In my opinion, cantProceed() does more harm than good as long as it is not able to provide useful debug information (at least a stack trace) -- which is probably hard to do in a portable way. I think, a call to abort() would be more helpful as it produces a process dump (at least on Unix systems) which can be analyzed.

Generally, error handling should not be part of the low-level functions. These functions do not have any application knowledge and thus cannot decide if suspending the thread, terminating the program, printing an error message or continuing normally is the "correct" behavior. Instead, low-level functions should only report errors (by or exceptions or return values -- I am not religious in this matter) and leave the choice of the correct response to the caller.

In this case, the gateway (maybe the CAS library) stopped accepting new clients which made it effectively useless. On the other hand, it did not terminate. Thus any mechanism to restart the gateway on failure does not work, too. I do not consider this a "useful" behavior.

It may be a goal of the next codathlon to improve the error messages provided by EPICS.

Dirk



Replies:
Re: Useless error messages in EPICS Bob Soliday
Re: Useless error messages in EPICS Dirk Zimoch
References:
Useless error messages in EPICS Dirk Zimoch

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