LabVIEW provides three VI reentrancy options that determine how your subVI executes when it is called at more than one point in the dataflow at the same time.
By default, LabVIEW executes each call to the subVI one after another. This may cause your application to execute slowly or have unexpected behavior. To allow multiple calls to a subVI to execute simultaneously, set a reentrant execution state for the subVI.