Re: How to safely implement an asynPortDriver with SCAN records

[Jure Varlec via Tech-talk <tech-talk at aps.anl.gov>]

I'm not sure killing the IOC with cantProceed() is the best way to handle this. Have you tried disabling the port as I suggested? You can modify your exit hook like so:

static void exitHandlerC(void *pPvt)    
{                                       

    drvFOFB *pdrvFOFB = (drvFOFB *)pPvt;

    pasynManager->enable(pdrvFOFB->pasynUserSelf, 0);

    delete pdrvFOFB;

}

This should be enough to prevent further calls into your driver, thus preventing the crash. It may print harmless error messages, but that's all.

Disabling the scan threads cannot be done without modifying epics-base. Running the hook at a different point (e.g. at initHookAfterStopScan) won't help, the threads are never​ stopped.

Best,

Jure

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov>
Sent: Wednesday, July 20, 2022 16:18
To: Michael Davidsaver <mdavidsaver at gmail.com>; Mark Rivers <rivers at cars.uchicago.edu>; Andrew Johnson <anj at anl.gov>
Cc: tech-talk <tech-talk at aps.anl.gov>
Subject: Re: How to safely implement an asynPortDriver with SCAN records

 

Caution: This email originated from outside of Cosylab.


On 08/07/2022 17:37, Michael Davidsaver wrote:
> On 7/8/22 11:11, Mark Rivers via Tech-talk wrote:
>> Hi Andrew,
>>
>> To be honest I have not paid enough attention to how to correctly
>> handle destructors in asynPortDriver.
>
> On the occasions when I've used asynPortDriver, I put a cantProceed()
> in the sub-class destructor.


Can you say where exactly in the destructor you used cantProceed()? I
can't seem to make it behave correctly: the IOC never exits, though it
does dump a stack trace.


>
> After a call to registerInterface(), the asynInterface::drvPvt pointer
> must remain valid until
> the process exits.  So an asyn port can't be destroyed.
>
>
> I've toyed with the ideas like re-counter asynUser, or somehow later
> setting drvPvt=NULL.
> Both seem possible, but not without quite some effort.
>
>
> This situation is made more complicated by the fact that IOC scan
> threads are not stopped on exit.
> We do now stop them during database unit tests.  However, some ~vague
> compatibility concerns have
> so far kept this from being done for full IOCs.


Where does this choice happen? Could one do it for their own IOC?


>
>
> Personally, as a matter of good practice, drivers I write always
> include an epicsAtExit() handler
> which stops any worker threads.
>
>
> Also, I should mention the de-init hooks added in Base 7.0.4 to
> decouple database shutdown from
> process exit.
>
> https://github.com/epics-base/epics-base/commit/5d5e552a7ec6ef69459c97b0081aa775372a6290#diff-02e4602d43dbb03b4097bb26382a1db92367fb55fe791415cd32d4f234875d92R50
>
>
> For compatibility, the effect of initHookAtShutdown can mostly be
> replicated by calling epicsAtExit()
> at initHookAfterIocRunning.


If I understand correctly, what I'd want for my own code would be
calling the driver's destructor in initHookAfterStopScan? If it ran for
full IOCs, of course.


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