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MPI_Bsend.3.rst

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MPI_Bsend

:ref:`MPI_Bsend` - Basic send with user-specified buffering.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Bsend(const void *buf, int count, MPI_Datatype datatype,
   int dest, int tag, MPI_Comm comm)

Fortran Syntax

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

Fortran 2008 Syntax

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

INPUT PARAMETERS

  • 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).

OUTPUT PARAMETERS

  • ierror : Fortran only: Error status (integer).

DESCRIPTION

:ref:`MPI_Bsend` performs a buffered-mode, blocking send.

NOTES

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.)

ERRORS