What does "skip subroutine call if busy" do???

Question

if i select this, what happens???

Answer 1

Hi,
I didn't know about this...
Is this a 'proper' feature of LabVIEW? It's not documented, and the most
simple example I could come up with, crashes (reproducable). LabVIEW
generates a bookkeep.cpp error, line 6??.
Regards,
Wiebe.
"Greg McKaskle" wrote in message
news:[email protected]...
> > if i select this, what happens???
> >
>
> This is a rather advanced bit of functionality that is useful when
> trying to do more deterministic applications where it is OK to sometimes
> skip a function.
>
> Lets say that you have a subVI that is called from multiple locations.
> If you leave the VI as non-reentrant, the calls will block waiting for
> each other to complete. This is fine for most situations, so it is the
> default.
>
> Another option is to make the subVI reentrant. This is appropriate when
> the subVI either doesn't have any state information/history so that one
> call affects another, or where you want the history to be kept separate.
> With a reentrant VI, the calls are totally separate and will not wait
> on one another -- they will run totally independent even simultaneously.
> Keep in mind that most computers only have one CPU, so simultaneous
> really means that the CPU takes turns or multitasks back and forth.
>
> Now the choice you asked about. If you set the priority of the subVI to
> be a subroutine, then you have a popup item on the node that lets you
> skip. This means that on a particular call, one of two things will
> happen. If the subVI isn't busy, if no other call is currently running,
> then this call will enter the subVI and run till completion. On the
> otherhand, if the subVI is already busy, if another call is already in
> there, just skip it without running. To tell the difference, make sure
> the subVI has an output that defaults to FALSE, but returns TRUE if the
> call completes.
>
> When is this option appropriate? If you have multiple calls to
> something like a logging VI where you pass in an array of the latest
> values, then you can set it to skip. If it logged the values, go
> collect some more and call it with just the new values. If it skipped,
> you can go collect some more, but append them to the old values before
> calling the logger. This allows your VIs to block less and lets them
> keep up with computational schedules. It is obviously useful only when
> a skipped call is acceptable and can be made up for in some way.
>
> Greg McKaskle
>