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MPI_Request_free - Frees a communication request object.
#include <mpi.h>
int MPI_Request_free(MPI_Request *request)
INCLUDE ’mpif.h’
MPI_REQUEST_FREE(REQUEST, IERROR)
INTEGER REQUEST, IERROR
#include <mpi.h>
void Request::Free()
- request
- Communication request (handle).
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 associated with the request will be allowed
to complete. The request will be deallocated only after its completion.
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 communication
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 ).
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;
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.
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
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