Hi all,
I've been using QControls extensively in my code base, and after intermittently encountering error 1556 (invalid reference), I believe there is a race condition in QControls.
To Recreate:
1.) Add cleanup code to Event Handler which accesses the State Data DVR. The cleanup code must take some time to complete. You can add a delay here to make sure you encounter the race condition.
2.) Run the QControl as you would normally
3.) Close the QControl
4.) The Event Handler should throw error 1556.
Reason:
The Close Event Handler VI doesn't wait for the Event Handler to close before closing the State Data DVR. If the Event Handler attempts to access the State Data after it has been closed, then Error 1556 (invalid reference) is thrown.
Proposed Solution:
1.) Add a notifier to the Control.lvclass that notifies the Close Event Handler.vi when the Event Handler Dispatcher.vi is done executing.
2.) Change Close Control.vi in Control.lvclass to Shared Clone Reentrant Execution. (This will require a bunch of other VIs which rely on this VI to change their reentrancy settings).
I have been personally running the above proposed solution for several months without issue. I made a GIT merge request a while ago, but I've just recently closed it after not getting a response for a long time and realizing the long reaching changes required by the reentrancy setting change. Here is the original merge request. It has images of proposed code changes included.
https://gitlab.com/QSI_Shared_Code/SharedQControls/QControlToolkit/-/merge_requests/1
Nora Clark
