you are looking for is called an “inter-application communication”.
There are several options to realize it. LabVIEW supports TCP/IP, ActiveX or UDP to communicate with another application. So it’s not as simple as using a “global Boolean” as you mentioned.
I advise you, to use the LabVIEW examples which shipped with the NI example finder to get some programs as reference. Search for keywords like TCP/IP, ActiveX and UDP.
Attached you’ll find a link to a knowledgebase.
Hope this helps.
How Do I Use LabVIEW to Communicate with Other Applications?