How can I allow a sub-vi to run independent of the main program once it has been called while still sending data to the sub-vi

Question

I have a main program where I call a sub-vi. In this sub-vi, there is a while loop that is used to wait for commands in the sub-vi. While the while loop is running, I cannot continue with normal operation of the main program. I would like get the sub-vi to run independently once it has been called, but not hold up the main program. As well, I need to still be able to send data to the sub-vi

Answer 1

One way is to use VI Server, which has been mentioned by others. This will allow you to start another VI (by name) and run it entirely independently of the calling VI. This is a good way to start various independent VIs from a main menu, for example. None of the VIs thus called need have any connection to the others.
Another way it to have the SubVI in a separate while loop on the calling VI's BD. Then, use a local var to start this sub VI from the main loop. The calling VI sets a local START bit and continues running. The sub VI's while loop watches for this START bit to go true, and then runs the Sub VI. The advantage here is that one can more easily pass arguments to the SubVI when it is started, using local vars, which are preferable to globals. Once the Su
bVI is running, however, you must use a global Stop Bit, set in the calling VI, to stop it when the calling VI exits, or the calling VI will hang up, waiting for the Sub VI to close and exit its while loop.
If you need an example of this, email me. ([email protected]). I can also recommend Gary W. Johnson's excellent book which discusses this. ("LabVIEW Graphical Programming", 2nd Ed).
Note: Where possible, I try to call a subvi from within the main VI, wait till it is done, then continue. It avoids the use of locals & globals, and results in cleaner code, with fewer "race" conditions. However, the main VI stops until the subVI is done, hence one should make the subVI modal.