Expose "Call Chain" as VI Property

[TurboPhil]

The only way I know of getting the call chain of a VI is with the Call Chain primitive, which only works on *this* VI (the VI calling the primitive). It would be nice to expose that as a VI server property, so we could get the call chain of any VI by reference.

[PaulG.]

I'm surprised we can't do that already.

[Bob_Schor]

I don't have an example on which to try this out, but I believe if the VIs are in memory, this is easily accomplished:

Of course, this lists all of the VIs that can call VI Refnum -- if that is a "popular" sub-VI, going up the chain can quickly get out of hand.

[JimChretz]

I unkudoed because Bob just cleared that out.

Of course we can't have the Call chain of a VI reference because one VI can be used in multiple contexts simultaneously, so the same VI can have several call chain arrays depending on where it's actually running, that's why we have to use the function in the code to have the actual chain...

I think with recursivity we can build the entire tree structure of the VIs in memory.

[TurboPhil]

Callers is not the same as Call Chain.

• It only presents the immediate caller (parent), not older generations (e.g. grandparents/caller's caller, etc.)
• Yes, you could theoretically do this recursively to get older generations, except:
• For reentrant VIs, it returns all callers of all instances. If I want to know the immediate caller of a specific clone instance, this won't work.

[JimChretz]

I'm not convinced about your reentrant concern, have you tested it?

Each clone instance has its own reference and VI name, somevi.vi:1, somevi.vi:2... so they should have their own callers list, which contain only one caller each.

[TurboPhil]

Yes, I have tested it. Look at this example (sorry it's kinda sloppy):

Notice that I get the same list of "Callers" both from the static VI reference (so, basically the "template" for the reentrant VI) as well as for a specific clone instance.

[CoastalMaineBird]

Like I said on the forum thread, I don't see how this can possibly work.

If A calls X

and B calls X

and C calls D which calls X,

then what is the "call chain" for X?

Go ahead, tell me, I'll wait.

If you answered anything except "I don't know" then you're wrong.

Call Chain is a trail of EXECUTION control.  It's possible WITHIN a VI instance, because you're talking about one instance, at one point in time.

If X is reentrant, then all three instances of X could be executing at the same time.  Which call chain do you mean?

If X is NOT reentrant, then which call chain do you mean? A, B, or C-->D ?  The refnum isn't going to tell you that.

It can't be done.

[CMal]

I agree that it doesn't make any sense to try to get a VI's call chain from a VI reference. A VI reference is specific to one instance of a VI, but that instance may be called in many different locations, each of which will have a different call chain. The "call chain" simply isn't a property of a VI. It's a property of the execution of a VI. I don't see any way this idea could be implemented.

[JimChretz]

It might make sense to have this property that would return a 2D array or array of clusters containing all the different call chains.

[igagne]

You want the one instance that's on the wire sort of like the exec.state property method. In the above example you'd get an array with just the callee because its being dynamically called.