Receive operations posted by a process are also ordered in a sequence. Each incoming message matches the first matching receive in the sequence. This is illustrated in Figure . Process zero sends two messages to process one and process two sends three messages to process one. Process one posts five receives.
All communications occur in the same communication domain.
The first message sent by process zero and the first message sent by process two can be received in either order, since the first two posted receives match either. Messages are matched in order. Thus, if a sender sends two messages in succession to the same destination, and both match the same receive, then the receive cannot get the second message if the first message is still pending. If a receiver posts two receives in succession, and both match the same message, then the second receive operation cannot be satisfied by this message, if the first receive is still pending. These requirements further define message matching.