Problems with ActiveX Callbacks in LabVIEW 7

Question

Have encountered an interesting problem with ActiveX "Reg Event Callback" in LV7 (WinXP):
In a nutshell, when a lot of events fire in rapid succession, the user-interface locks up.
The events still fire, and the front panel controls update, but the front panel will not respond to clicks. Interestingly, if the block diagram is open, you can stop it and turn on execution highlighting, etc...
- I've discovered that the problem we're encountering is related to multiple events firing before the (reentrant) callback VI has finished executing from the 1st event.
- by watching the Performance data in task manager, and tracking the # of handles used by LabVIEW, I find that when this happens, the # of handles increases, b
ut never decreases until you stop the VI
- I would expect several (nearly) instantaneous events to launch multiple copies of that callback VI, and I can believe that would increase the # handles, but I would expect that LabVIEW would catchup shortly thereafter and the # handles would return to its starting count.
As an aside, using the old ActiveX event and callback method with the exact same version of the activeX control does not have this problem, events just queue up and then fire appropriately.
Anyone seen anything like this?
Anyone (NI guys) have any ideas?
Follow up question (NI guys): when will the support for the old ActiveX event stuff dry up?
Thanks in advance,
Ben
Ben Zimmer
[email protected]
Software Developer
Meikle Automation

Answer 1

Hi Ben,
The error message warns about the use of three ActiveX Event VIs that will no longer be supported in future versions of Labview. Following version 6 of Labview, the use of ActiveX Event VIs is shifting to the use of Register Event Callback VI instead. In looking at your screenshots, I did not see any use of the older ActiveX Event VIs. If possible, try attaching the actual VI to the post and I will take a look at that.
At least in terms of support, phone support currently exists for Labview 6 and 7. With the release of Labview 8, support for Labview 6 will slowly be phased out. In this case, phone support for the ActiveX Event VIs will no longer continue as they are no longer included in the versions of Labview for
which phone support is provided. However, Discussion Forums and web-based resources would be your best venue of support for those features.
I would strongly recommend that you migrate to replacing ActiveX Event VIs to using the Register Event Callback VI. The following is a KnowledgeBase article describing the transition of ActiveX in Labview:
Migrating from the ActiveX Event VIs to Using the Register Event Callback Node
Also, are you using the Automation Open/Close VIs? These two VIs will allow acquire/release informatio nof the ActiveX object. I have attached a couple example programs that are included in Labview to help demonstrate this concept.
Hope this helps!
Kileen Cheng
Applications Engineer
National Instruments
Attachments:
ActiveX_Event_Callback_for_Excel.llb ‏944 KB
ActiveX_Event_Callback_for_IE.llb ‏972 KB