Blocking semantics

Blocking semantics

By default—or if SYNCHRONOUSLY is specified—messages are sent synchronously. That is, a sender blocks (i.e., waits) until the message buffer is safe to reuse before it continues and a receiver blocks until it actually receives the message. The ASYNCHRONOUSLY keyword specifies that messages should be sent and received asynchronously. That is, the program merely posts the message (i.e., declares that it should eventually be sent and/or received) and immediately continues executing. Asynchronous messages must be completed as described in Awaiting completion.