MPI_Wait(3)                        Open MPI                        MPI_Wait(3)



NAME
       MPI_Wait - Waits for an MPI send or receive to complete.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Wait(MPI_Request *request, MPI_Status *status)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_WAIT(REQUEST, STATUS, IERROR)
            INTEGER   REQUEST, STATUS(MPI_STATUS_SIZE), IERROR


C++ Syntax
       #include <mpi.h>
       void Request::Wait(Status& status)

       void Request::Wait()


INPUT PARAMETER
       request   Request (handle).


OUTPUT PARAMETERS
       status    Status object (status).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       A call to MPI_Wait returns when the operation identified by request is
       complete. If the communication object associated with this request was
       created by a nonblocking send or receive call, then the object is
       deallocated by the call to MPI_Wait and the request handle is set to
       MPI_REQUEST_NULL.

       The call returns, in status, information on the completed operation.
       The content of the status object for a receive operation can be
       accessed as described in Section 3.2.5 of the MPI-1 Standard, "Return
       Status." The status object for a send operation may be queried by a
       call to MPI_Test_cancelled (see Section 3.8 of the MPI-1 Standard,
       "Probe and Cancel").

       If your application does not need to examine the status field, you can
       save resources by using the predefined constant MPI_STATUS_IGNORE as a
       special value for the status argument.

       One is allowed to call MPI_Wait with a null or inactive request
       argument. In this case the operation returns immediately with empty
       status.


NOTES
       Successful return of MPI_Wait after an MPI_Ibsend implies that the user
       send buffer can be reused  i.e., data has been sent out or copied into
       a buffer attached with MPI_Buffer_attach. Note that, at this point, we
       can no longer cancel the send (for more information, see Section 3.8 of
       the MPI-1 Standard, "Probe and Cancel"). If a matching receive is never
       posted, then the buffer cannot be freed. This runs somewhat counter to
       the stated goal of MPI_Cancel (always being able to free program space
       that was committed to the communication subsystem).

       Example: Simple usage of nonblocking operations and  MPI_Wait.

           CALL MPI_COMM_RANK(comm, rank, ierr)
           IF(rank.EQ.0) THEN
               CALL MPI_ISEND(a(1), 10, MPI_REAL, 1, tag, comm, request, ierr)
               **** do some computation ****
               CALL MPI_WAIT(request, status, ierr)
           ELSE
               CALL MPI_IRECV(a(1), 15, MPI_REAL, 0, tag, comm, request, ierr)
               **** do some computation ****
               CALL MPI_WAIT(request, status, ierr)
           END IF


ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI::Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler, MPI_File_set_errhandler, or
       MPI_Win_set_errhandler (depending on the type of MPI handle that
       generated the request); the predefined error handler MPI_ERRORS_RETURN
       may be used to cause error values to be returned. Note that MPI does
       not guarantee that an MPI program can continue past an error.

       Note that per MPI-1 section 3.2.5, MPI exceptions on requests passed to
       MPI_WAIT do not set the status.MPI_ERROR field in the returned status.
       The error code is passed to the back-end error handler and may be
       passed back to the caller through the return value of MPI_WAIT if the
       back-end error handler returns it.  The pre-defined MPI error handler
       MPI_ERRORS_RETURN exhibits this behavior, for example.


SEE ALSO
       MPI_Comm_set_errhandler
       MPI_File_set_errhandler
       MPI_Test
       MPI_Testall
       MPI_Testany
       MPI_Testsome
       MPI_Waitall
       MPI_Waitany
       MPI_Waitsome
       MPI_Win_set_errhandler




1.4.1                            Jan 14, 2010                      MPI_Wait(3)
