The Virtual Logic Analyzer is a development tool for monitoring VI execution. It is especially useful for optimizing the performance of multi-threaded, parallel applications. Monitoring Data and Timing information over an entire application can provide unexpected insight into performance bottlenecks. The VLA Probes use the OOP model Stepan Riha of NI introduced at NIWeek 97 and the Virtual Logic Analyzer concept is based on the presentation "Monitoring the Control and Timing of VIs" by Dana Redington at NIWeek95.

There are two parts to the Virtual Logic Analyzer: Probes, and the GUI interface. Probes are meant to be as efficient as possible, but do not place them in a MHz type loop. Instead place them in strategic locations where you can monitor program flow. Each VLA Probe is a reentrant vi that monitors your program's execution by timestamping data during program execution. Simply place this vi on your block diagram and connect the required Tag and Data inputs. Remember that dataflow governs LabVIEW execution. Be sure to give each Probe a unique Tag.

Probes can be on a local or remote machine. Because Probes are OFF by default they can be left in an application and individually switched on or off later with the GUI application. To view and interact with the probes run the Virtual Logic Analyzer application. In the Info tab of the VLA application is a multi-column listbox with a live display of active probes. Double-click on a probe to turn it on in the application you are monitoring. You can turn on as many or as few probes as you need. Live data is displayed in the graph on the Data tab. Note that data is only displayed for probes that are turned on.

Ideally the VLA GUI interface should be run on a separate computer from the application being monitored. This eliminates the GUI overhead from impacting application performance. The VLA interface uses VI Server calls to interface to the Probe Registry.