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MPI_Wait - Waits for an MPI send or receive to complete.
#include <mpi.h>
int MPI_Wait(MPI_Request *request, MPI_Status *status)
USE MPI
! or the older form: INCLUDE ’mpif.h’
MPI_WAIT(REQUEST, STATUS, IERROR)
INTEGER REQUEST, STATUS(MPI_STATUS_SIZE), IERROR
USE mpi_f08
MPI_Wait(request, status, ierror)
TYPE(MPI_Request), INTENT(INOUT) :: request
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
- request
- Request (handle).
- status
- Status
object (status).
- IERROR
- Fortran only: Error status (integer).
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.
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
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.
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
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