Re: How to safely implement an asynPortDriver with SCAN records

[Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov>]

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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