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
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_WAIT(REQUEST, STATUS, IERROR)
INTEGER REQUEST, STATUS(MPI_STATUS_SIZE), IERROR
Fortran 2008 Syntax
USE mpi_f08
MPI_Wait(request, status, ierror)
TYPE(MPI_Request), INTENT(INOUT) :: request
TYPE(MPI_Status) :: status
INTEGER, OPTIONAL, INTENT(OUT) :: 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 de-
allocated 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 ac-
cessed 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 argu-
ment. 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++ 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, MPI_File_set_errhandler, or MPI_Win_set_er-
rhandler (depending on the type of MPI handle that generated the re-
quest); 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
4.1.2 Nov 24, 2021 MPI_Wait(3)
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