For MPI programs, use the Process Window’s Message Queue Graph (Tools > Message Queue Graph) to display your program’s message queue state.

The graph’s Options window (available by clicking on the Options button, above) provides a variety of useful tools, such as Cycle Detection to generate reports about cycles in your messages, a helpful way to see when messages are blocking or causing deadlocks. Also useful is its filtering capability, which helps you identify pending send and receive messages, as well as unexpected messages.