order, nonblocking, order Nonblocking communication operations are ordered according to the execution order of the posting calls. The non-overtaking requirement of Section is extended to nonblocking communication.
The order requirement specifies how post-send calls are matched to post-receive calls. There are no restrictions on the order in which operations complete. Consider the code in Example .
Since the completion of a receive can take an arbitrary amount of time, there is no way to infer that the receive operation completed, short of executing a complete-receive call. On the other hand, the completion of a send operation can be inferred indirectly from the completion of a matching receive.