:ref:`MPI_Bsend` |mdash| Basic send with user-specified buffering.
#include <mpi.h>
int MPI_Bsend(const void *buf, int count, MPI_Datatype datatype,
int dest, int tag, MPI_Comm comm)
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_BSEND(BUF, COUNT,DATATYPE, DEST, TAG, COMM, IERROR)
<type> BUF(*)
INTEGER COUNT, DATATYPE, DEST, TAG, COMM, IERROR
USE mpi_f08
MPI_Bsend(buf, count, datatype, dest, tag, comm, ierror)
TYPE(*), DIMENSION(..), INTENT(IN) :: buf
INTEGER, INTENT(IN) :: count, dest, tag
TYPE(MPI_Datatype), INTENT(IN) :: datatype
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
buf
: Initial address of send buffer (choice).count
: Number of entries in send buffer (nonnegative integer).datatype
: Datatype of each send buffer element (handle).dest
: Rank of destination (integer).tag
: Message tag (integer).comm
: Communicator (handle).
ierror
: Fortran only: Error status (integer).
:ref:`MPI_Bsend` performs a buffered-mode, blocking send.
This send is provided as a convenience function; it allows the user to send messages without worrying about where they are buffered (because the user must have provided buffer space with :ref:`MPI_Buffer_attach`).
In deciding how much buffer space to allocate, remember that the buffer space is not available for reuse by subsequent :ref:`MPI_Bsend`s unless you are certain that the message has been received (not just that it should have been received). For example, this code does not allocate enough buffer space:
MPI_Buffer_attach( b, n*sizeof(double) + MPI_BSEND_OVERHEAD );
for (i=0; i<m; i++) {
MPI_Bsend( buf, n, MPI_DOUBLE, ... );
}
because only enough buffer space is provided for a single send, and the
loop may start a second MPI_Bsend
before the first is done making
use of the buffer.
In C, you can force the messages to be delivered by
MPI_Buffer_detach( &b, &n );
MPI_Buffer_attach( b, n );
(The
MPI_Buffer_detach
will not complete until all buffered messages are
delivered.)