Use a functional global variable (FGV) to communicate between two parallel process loops contained within different VIs under the same target, and use a FGV to stop parallel loops with one "stop" button. The "functional" nature of the FGV means that you can create additional functionality beyond that of a basic global variable, e.g., counting and calculations that operate on the stored value.
Use a channel wire to communicate between two (or more) parallel process loops contained within the same VI, and use a channel wire to stop parallel loops with one "stop" button. Requires LabVIEW 2016 or later version.
Send TCP/IP messages to a destination IP address and port number, listen for incoming TCP/IP messages on a user-defined port, and echo received messages back to the source. Combine the sender and receiver into a single "TCP ping" application to test the communication channel between two network hosts, and illustrate the notifier method to stop parallel loops with one "stop" button.