Error causes hang, no events get processed

[DEppAtNGC]

On a second system where I apparently do not have a VISA driver correctly installed, I receive an error: "Driver Status:  (Hex 0xBFFF009E) A code library required by VISA could not be located or loaded.".

This error is not a concern for the issue I'm reporting here; however, it appears to have a causal effect that I do not understand:

After this error occurs, the application appear to stop processing events; that is, there is an event structure that no longer seems to function and I can find no place where the application is looping. It simply appear to stop normal processing even though it is in a "run" status.

There is an Simple Error Handler.vi that pops up a dialog that indicates the error mentioned above; when I place a break on the error in to this VI, continue the application at the break, press ok on the error handler, the follow-on hang does NOT occur.

So all I need to do is disable the breakpoint and the hang condition re-occurs. So apparently, the "break" is somehow prevent an undesirable event processing disable or something like that. Breakpoint before the Simple Error Handler.vi, everything behaves as expected, breakpoint disabled, events become disabled. I tried putting a 500ms delay via stacked sequence before the Simple Error Handler to see if a race condition existed - no effect.

Any clues? I can work around this as it only occurs in my "offline" development system, but it's an interesting issue that I'd like to solve.

[SanRac]

HI

Can you please upload the VI?

Regards

Santosh

[Andrew_E]

Hello,

Does this problem only occur on the system that does not have VISA properly installed? What LabVIEW version is this? This is important to see if anyone else has had  similiar problem. Thanks.

[DEppAtNGC]

Yes, this occurs on the system where a driver is incorrectly installed. LV 8.6. Unfortunately, the VI is far too large and proprietary to upload. It's not high enough priority to duplicate at a smaller level at this time.

If there's any way to see what LV is doing when in this "events disabled" state, or re-enabling events, I'd be interested in learning how to do that.

[Andrew_E]

The best way to monitor your vi is to use highlight execution and see exactly where your application is not executing correctly. After you run highlight execution could provide a screenshot of the code where the program is stopping? Thanks.

[DEppAtNGC]

You have got to be kidding - right? 🙂 Seriously, this application is fairly large and uses an event loop and queue architecture... so since there are event timeouts that occur faster than the application can execute in debugging modes, single stepping and highlight execution don't really work well as debugging tools. I am considering re-writing those aspects of the applicaton I've inherited, but probably don't have time to do that...

[DEppAtNGC]

I did turn on highlight execution after the error occurs - and there appears to be no activity. Trying to turn it on before the error occurs and waiting for everything to get to a good check point could take a very long time.