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First Call? (G Dataflow)

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Last Modified: August 28, 2017

Indicates whether the diagram or subdiagram containing this node is running for the first time since the top-level caller began execution.

You can place First Call? in multiple locations within a program, such as the diagram of a VI, a subdiagram of a Case Structure, inside a loop, or the diagram of a subVI.

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First Call?

A Boolean value that indicates whether the diagram or subdiagram containing this node is running for the first time since the top-level caller began execution.

True This is the first time the diagram or subdiagram is running since the program began execution.
False This is not the first time the diagram or subdiagram is running since the program began execution.

Behavior for Multiple Top-Level Callers

First Call? returns True the first time the calling diagram or subdiagram runs after the first top-level calling VI starts running, such as when you click the Run button. If a second top-level caller calls the diagram or subdiagram 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.

Behavior with Reentrant VIs

A stateless reentrant VI has one instance of the VI per caller at compile time. Therefore, First Call? in a stateless reentrant VI returns True the first time a top-level caller calls each instance of the VI.

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Note  

Avoid using First Call? in a stateless reentrant VI because the node will return unpredictable results.

Where This Node Can Run:

Desktop OS: Windows

FPGA: DAQExpress does not support FPGA devices

Web Server: Not supported in VIs that run in a web application


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