Completion Operations

completion functions  

The functions MPI_WAIT and MPI_TEST are used to complete nonblocking sends and receives. The completion of a send indicates that the sender is now free to access the send buffer. The completion of a receive indicates that the receive buffer contains the message, the receiver is free to access it, and that the status object is set.

MPI_WAIT(request, status)

    INOUT    request              request handle
     OUT     status               status object

MPI_WAIT(REQUEST, STATUS, IERROR)INTEGER REQUEST, STATUS(MPI_STATUS_SIZE), IERROR

A call to MPI_WAIT returns when the operation identified by request is complete. If the system object pointed to by request was originally created by a nonblocking send or receive, then the object is deallocated by MPI_WAIT and request is set to MPI_REQUEST_NULL. MPI_REQUEST_NULL The status object is set to contain information on the completed operation. MPI_WAIT has non-local completion semantics.

MPI_WAIT(request, flag, status)

    INOUT    request              request handle
     OUT     flag                 true if operation completed
     OUT     status               status object

MPI_TEST(REQUEST, FLAG, STATUS, IERROR)LOGICAL FLAG
INTEGER REQUEST, STATUS(MPI_STATUS_SIZE), IERROR

A call to MPI_TEST returns flag = true if the operation identified by request is complete. In this case, the status object is set to contain information on the completed operation. If the system object pointed to by request was originally created by a nonblocking send or receive, then the object is deallocated by MPI_TEST and request is set to MPI_REQUEST_NULL. MPI_REQUEST_NULL The call returns flag = false, otherwise. In this case, the value of the status object is undefined. MPI_TEST has local completion semantics.

For both MPI_WAIT and MPI_TEST, information on the completed operation is returned in status. The content of the status object for a receive operation is accessed as described in Section . The contents of a status object for a send operation is undefined, except that the query function MPI_TEST_CANCELLED (Section ) can be applied to it.