Open VI Reference (G Dataflow)

Configuring References for Dynamic VI Calls

If you want to call the specified VI dynamically with Call by Reference or Start Asynchronous Call, you must use appropriate data for the following items:

• type specifier VI reference (for type only)—Wire a strictly typed VI reference to this input.
• Item tab—Use the Item tab for this node to configure the type of call you want to make:
  • Enable simultaneous calls on reentrant VIs
    • Prepare for run or synchronous call—Uses Run VI to run multiple instances of a reentrant target VI in parallel. Setting this option causes the application to allocate a dedicated parallel data space in which a clone of the target VI can run. Without this option, Open VI Reference always returns a reference to the same data space of the original target VI, preventing multiple calls to that VI from executing simultaneously.
    • Prepare for asynchronous call without wait—Prepare to call and forget: Use this option when you want to call a target VI asynchronously with Start Asynchronous Call but you do not need to know when or what the VI returns.
    • Prepare for asynchronous call with wait—Prepare to call and collect: Use this option when you want to collect the results of an asynchronous call to a target VI with Wait on Asynchronous Call. If you use this option, you must include one Wait on Asynchronous Call for every call that you begin with a Start Asynchronous Call node to ensure that the application does not retain any started calls in memory indefinitely.

Criteria for Opening Strictly Typed References

If you wire a strictly typed VI reference to the type specifier VI reference (for type only), the VI that vi name specifies must meet the following criteria:

• The VI cannot be broken.
• The VI cannot be active as a top-level VI unless the VI is reentrant.
• The connector pane of the VI must match the connector pane of type specifier VI reference (for type only).

Opening References to Reentrant VIs

Aborting Open References

You can abort all open VI references either manually from the front panel of the VI or by using Abort VI. However, VI references prepared for asynchronous execution have important caveats depending on how you configure the reference:

• Prepare for asynchronous call without wait—A call-and-forget VI aborts only if you manually abort it from its front panel or call Abort VI on it. Otherwise, the VI runs to completion, even if you close the reference or abort the calling VI.
• Prepare for asynchronous call with wait—Call-and-collect VIs abort for the following reasons:
  • You abort the VI that opened the call-and-collect VI reference. In this case, the application aborts all running instances of the VI.
  • You manually abort a specific instance of the VI. In this case, exactly one Wait on Asynchronous Call node returns an error indicating that the called VI aborted. All other Wait on Asynchronous Call nodes that are waiting on calls to the same VI reference continue waiting.
  • You call Abort VI on the call-and-collect VI reference. In this case, the application aborts all currently running instances of the VI. A corresponding number of Wait on Asynchronous Call nodes return errors.

Closing Open References

After you finish using a reference that you obtain with this function, close the reference with Close Reference. Explicitly closing a reference enables the application to free the resources involved in maintaining that reference, thereby contributing to optimal memory allocation and performance. Otherwise, the application cannot close the reference until the VI that opened the reference finishes executing.

Note  

Closing a reference that was opened with the Prepare for asynchronous call without wait configuration does not abort the referenced VI.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

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