I need to execute a section of the code only when a particular subvi is called for the first time by a second top-level caller. Now the obvious problem with using the 'first call?' function is that identifies the first call since the start of the top-level VI. Is there a way to identify the first calls since the start of the second top-level vi. As my second top-level vi has to open and close multiple times

Sorry to drag us back a page, but did you look at what I posted (probably the last post on the first page, based on the default 10 posts per page). I'm not sure given the posts that followed if it does what you want or not, but if not perhaps you can clarify. In the code you uploaded now, C does indeed have an input to indicate the special behaviour (first time call in B) and presumably using that (via e.g. the case structures in C) is not a problem. Doing the same for D and E (or other hypothetical subVIs) is also not a problem. As to how B notifies C, this is via the block diagram of B. In your example, it appears that B has an interactive front panel, and that its execution flow is not known at edit time - is this correct? If so, I'd suggest doing something like the following (in B): Obviously this doesn't handle other cases (but you could move the Format to String and Set Variant Attribute outside of the Case Structure if you need to handle all cases). Also, it's not obvious what your full application will do, but this should be a usable technique (with a Variant on an shift register in B, using attributes with a dummy value to check if the value is overwritten). Edit: 2019 snippet to demonstrate perhaps more clearly:

LabVIEW

Identify if the subvi is called for the first time by a second top-level VI

Solved!

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Thank you so much for the inputs. I learnt something really useful from the solution you have provided. I would have never thought of setting the flag high or low for the first time in that manner, I am learning that with a few tweaks I could apply that to various other sections of my code for different purposes.