Determine if USB-GPIB port is in use

[Mythilt]

Is there any way to determine if a VISA resource is in use programmatically?

I have a situation where I will be running two copies of the same application on one system.  This application communicates via GPIB with a Spectrum Analyzer.  There are times when we will be wanting to collect data from two separate analyzers, and due to space constrictions, can only use a single computer.  Thus I need to run the compiled application twice at the same time.  My main question is, is there a way to have the program determine if its default VISA resource is already in use, and thus to use the secondary?  ie.  Program launches, and checks the VISA alias HPSpecAn1, and if it is not in use, starts to communicate with the spectrum analyzer referenced in the alias, but if another program has already claimed that resource (either that alias or another device on that GPIB bus.) it will go to the VISA alias HPSpecAn2 etc.

[Dennis_Knutson]

I think you can use the VISA Lock functions. At the beginning of where the instrument is required, you would do a VISA Lock Async set to a small timeout. If it returns with no error, the resource is available. If it does return an error, then open a reference to the other instrument. Don't forget to add a VISA Unlock when you are done.

[Mythilt]

That is basically what I ended up doing after some experimentation.  Thank you for confirming it as a good method.