Synchronous message passing

A message passing discipline in which a send completes only when a matching receive accepts the message. This rendezvous transfers both data and control dependencies: an unready recipient can block a service and thereby delay its other clients. A reply is a separate send unless the interface supplies synchronous send-and-receive.

A system call that sends a request and commits the caller to receiving the matching reply as one coordinated operation, often named sendrec. It avoids the gap in which a client has completed a send but has not yet entered a receive. It does not make the service nonblocking or eliminate deadlock caused by other circular dependencies.