First Call? Function

Owning Palette: Synchronization VIs and Functions

Requires: Base Development System

Indicates that a subVI or section of a block diagram is running for the first time. The First Call? function returns TRUE only the first time you call it after you click the Run button.

You can place the First Call? function in multiple locations within a VI. The function returns TRUE the first time the section of the block diagram in which it is placed runs.

Details  

Add to the block diagram

Find on the palette

First Call? is TRUE if the subVI is running for the first time since you ran the entire VI.

First Call? Details

This function is useful if you want to run a subVI or a section of a block diagram within a loop or Case structure only once when the VI runs.

First Call? returns TRUE the first time the VI runs after the first top-level caller starts running, such as when the Run button is clicked or the Run VI method executes. If a second top-level caller calls the VI while the first top-level caller is still running, First Call? does not return TRUE a second time. After all the top-level callers become idle and a top-level caller starts again, First Call? returns TRUE the first time the VI runs after the idle state. Reentrant VIs have an instance per data space. Therefore, a shared reentrant VI returns TRUE for each data space instance the first time its top-level caller calls it.