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MPI_Wait(3OpenMPI)                                                                        MPI_Wait(3OpenMPI)



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 sta-tus.MPI_ERROR status.MPI_ERROR
       tus.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 han-dler handler
       dler 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




Open MPI 1.2                                     March 2007                               MPI_Wait(3OpenMPI)