MPI_Request_free(3OpenMPI)												MPI_Request_free(3OpenMPI)

NAME

       MPI_Request_free - Frees a communication request object.

SYNTAX

C Syntax
       #include <mpi.h>
       int MPI_Request_free(MPI_Request *request)

Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_REQUEST_FREE(REQUEST, IERROR)
	    INTEGER   REQUEST, IERROR

C++ Syntax
       #include <mpi.h>
       void Request::Free()

INPUT
/OUTPUT PARAMETER
       request
		       Communication request (handle).

DESCRIPTION

       This operation allows a request object to be deallocated without waiting for the associated communication to complete.

       MPI_Request_free  marks the request object for deallocation and sets request to MPI_REQUEST_NULL. Any ongoing communication that is associ-
       ated with the request will be allowed to complete. The request will be deallocated only after its completion.

NOTES

       Once a request is freed by a call to MPI_Request_free, it is not possible to check for the successful completion of the associated communi-
       cation with calls to MPI_Wait or MPI_Test. Also, if an error occurs subsequently during the communication, an error code cannot be returned
       to the user -- such an error must be treated as fatal. Questions arise as to how one knows when the operations have  completed  when  using
       MPI_Request_free. Depending on the program logic, there may be other ways in which the program knows that certain operations have completed
       and this makes usage of MPI_Request_free practical. For example, an active send request could be freed when the logic  of  the  program	is
       such that the receiver sends a reply to the message sent -- the arrival of the reply informs the sender that the send has completed and the
       send buffer can be reused. An active receive request should never be freed, as the receiver will have no way to verify that the receive has
       completed and the receive buffer can be reused.

       Example:

	   CALL MPI_COMM_RANK(MPI_COMM_WORLD, rank)
	   IF(rank.EQ.0) THEN
	       DO i=1, n
		 CALL MPI_ISEND(outval, 1, MPI_REAL, 1, 0, req, ierr)
		 CALL MPI_REQUEST_FREE(req, ierr)
		 CALL MPI_IRECV(inval, 1, MPI_REAL, 1, 0, req, ierr)
		 CALL MPI_WAIT(req, status, ierr)
	       END DO
	   ELSE    ! rank.EQ.1
	       CALL MPI_IRECV(inval, 1, MPI_REAL, 0, 0, req, ierr)
	       CALL MPI_WAIT(req, status)
	       DO I=1, n-1
		  CALL MPI_ISEND(outval, 1, MPI_REAL, 0, 0, req, ierr)
		  CALL MPI_REQUEST_FREE(req, ierr)
		  CALL MPI_IRECV(inval, 1, MPI_REAL, 0, 0, req, ierr)
		  CALL MPI_WAIT(req, status, ierr)
	       END DO
	       CALL MPI_ISEND(outval, 1, MPI_REAL, 0, 0, req, ierr)
	       CALL MPI_WAIT(req, status)
	   END IF

       This  routine is normally used to free persistent requests created with either MPI_Recv_init or MPI_Send_init and friends.  However, it can
       be used to free a request created with MPI_Irecv or MPI_Isend and friends; in that case the use can not use the test/wait routines  on  the
       request.

       It is permitted to free an active request.  However, once freed, you can not use the request in a wait or test routine (e.g., MPI_Wait ).

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++ func-
       tions 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; 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.

SEE ALSO

       MPI_Isend
       MPI_Irecv
       MPI_Issend
       MPI_Ibsend
       MPI_Irsend
       MPI_Recv_init
       MPI_Send_init
       MPI_Ssend_init
       MPI_Rsend_init
       MPI_Test
       MPI_Wait
       MPI_Waitall
       MPI_Waitany
       MPI_Waitsome
       MPI_Testall
       MPI_Testany
       MPI_Testsome

Open MPI 1.2							  September 2006					MPI_Request_free(3OpenMPI)