Application freezing while in foreground sporadically

Question

Greetings. Occasionally my application's front panel will freeze, and not update any of the indicators or notice commands from controls, but only while it is in the foreground. As soon as I click on the desktop or another application, it recovers and works as expected. If I let it stay frozen, one of my two threads (the one that doesn't do any work with the front panel) times out, flags an error, and the thread that does work with the front panel inexplicably catches it and throws up a dialog box, after which things work normally. If I turn off the background thread's timeout, then after a long while (30-60 seconds) it will recover, sometimes just for a second and then going back to being frozen. Any ideas as
to why this might be happening, and what I can do about it? Thanks!

Answer 1

This may help some....
On Wed, 26 Nov 2003 23:50:22 +0100, robert_s wrote on Re:
Multithreading issue:
A couple of days ago, I wrote about a goal I need to achieve
in programming a rack for radar transponders:
>I have built a simplified version of what I want to do, but
>it does not work as expected: full screen VI A has an
>indicator that displays global variable V, and a button that
>launches modal VI B. In VI B, a command modifies global
>variable V. VI B's window is centered on the screen, but the
>indicator in VI A is visible. When modifying variable V from
>VI B, nothing happens on VI A' indicator until after I close
>VI B. Obviously this is not what I want to do...
>
>I tried to remove VI B's "modality" but this does make the
>problem disappear.
After carefully reading the docs, I ran many tests in order
to have two VIs, one caled by the other, to multitask
gracefully. As I said above, I never could make this happen,
particurlarly by enabling multithreading, affecting
different threads of execution to each VIs, playing on
execution priority, etc.
A friend who by profession is much more proficient with LV
than I am gave me the solution, and here it is:
VI A the caller should have two While loops, with a "WAit"
function of say 100ms; one loop is in charge of continuously
displaying global variable V on the indicator, the other of
calling VI B.
VI B itself consists of a while loop where a command feeds
and modifies global variable V. B is modal and centered, so
it won't hide the indicator on A.
This indicator is correctly updated on A when V is modified
on B.
There is a problem, though: in VI A, the two loops cannot be
exited under the action of an "armed" button (VI won't
compile). One must use a simpler button type.
One things to be noted is that *this architecture works even
with multithreading disabled in LV!!!*.
Why this works at al is beyond me, but I would appreciate
explanations however.
For now I can go back to programming my stuff the way I like
(well, the way the client said it should be programmed 8-)
Many thanks to the two persons that tried to help me.