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Wait on Asynchronous Call (G Dataflow)

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Last Modified: February 28, 2020

Causes the diagram to wait for an asynchronous call to a target VI to finish executing and then returns the outputs of the target VI.

To use the this node on a reference, navigate to the Item tab for Open VI Reference and select Prepare for asynchronous call with wait. You also must call the target VI with Start Asynchronous Call.

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reference in

A reference to a target node that you want to call asynchronously. The reference must meet the following criteria:

  • Be strictly typed.
  • Be configured for asynchronous execution with Open VI Reference. In the Item tab for Open VI Reference, select Prepare for asynchronous call without wait or Prepare for asynchronous call with wait.
  • Be called by a Start Asynchronous Call node elsewhere in the calling VI.
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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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reference out

Unchanged reference associated with the strictly typed VI reference.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Accessing Inputs and Outputs

The interface of this node includes the following features:

  • No access to inputs of the target VI—Wait on Asynchronous Call does not provide access to the inputs of the target VI. You can pass inputs to the target VI when you call it with Start Asynchronous Call.
  • Access to outputs of the target VI—When you wire a strictly typed VI reference to the reference in input of Wait on Asynchronous Call, the node displays the output portion of the connector pane of the referenced VI. Use the output terminals of the connector pane to access the data returned by the target VI.

Wait Behaviors

This node exhibits the following wait behaviors:

  • Ability to wait for only a specified amount of time—To specify how long this node waits for the associated asynchronous call to complete, select Timeout from the Item tab to specify how long the node waits on the corresponding VI call before returning a timeout error.
  • Ability to wait on multiple calls to the same VI reference—If you pass the same VI reference to multiple Start Asynchronous Call nodes, you cannot predict which Wait on Asynchronous Call node will detect the completion of each call. You can take precautions to match a Wait on Asynchronous Call node to a specific VI call if necessary.

Conserving Memory by Releasing References

You can call this node before the corresponding Start Asynchronous Call node.

Every Start Asynchronous Call node that uses a reference configured as Asynchronous with wait must have a corresponding Wait on Asynchronous Call. If you start an asynchronous call to a call-and-collect reference, the application cannot free the reference until a Wait on Asynchronous Call node collects the outputs of the VI call to that reference.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

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

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