LabVIEW crashes without message after executing Actors

[StevenHowell]

"If Instance 1 closes, then you try to launch a third one, it will reuse the memory space of Instance 1. Things like "First call?", uninitialized shift registers, etc do NOT get reset to a "clean" state. You may even still have values in indicators. I suspect this is the standard behavior for "Shared clones" reentrancy but I haven't dug into it outside of AF."

Bert thanks for sharing this tidbit of information. I realize this is an older thread but I just read through this and it is insightful and made me think back to some recent bizarre behavior I have seen.

What are some strategies that you use to get around First Call? but get the same functionality?

[BertMcMahan]

Glad I could help. It really drove me nuts until I figured out what was going on.

When I have reuse actors that need uninitialized shift registers, First Call, etc, then I just store that as state data in the Actor's private data. I like to explicitly set state variables like this to "not initialized" in Pre launch init*. When a function needs something like a First Call primitive, then just read from that state variable instead.

I have stopped using First Call? altogether as it seems to always bite me somewhere down the line. It's super convenient at times, but when you get into reuse VI's, clones, etc then it becomes much less reliable since you can't explicitly reset it. So, I just decided to stop using it. It's a touch more work to add a state variable or two but it only takes about 5 minutes and can save a whole day of trying to figure out exactly WHICH part isn't initializing the right way.

I'd suggest using an enum for the state variable as well. If I had a nickel for every time I thought "Yeah, I only need two states here, a Boolean will be fine" then had to add a third state later, I'd retire now 🙂

*I say you don't have to explicitly initialize the state variables, as whatever launches your actor generally does so with either a block diagram constant or with a factory pattern that loads the default value of an actor into memory. Generally speaking, the default values of a Boolean variable like Initialized? would be False, so you don't HAVE to explicitly initialize them to False... but it's good practice to do so anyway. Default values can be tricky to debug, and if you ever change to more than 2 states, you may need to explicitly set the initial state to something else anyway. Plus, it doesn't take much code to just write a value as "False" or "Uninitialized".