.. _mpi_bsend:

MPI_Bsend
=========

.. include_body

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

SYNTAX
------

C Syntax
^^^^^^^^

.. code-block:: c

   #include <mpi.h>

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

Fortran Syntax
^^^^^^^^^^^^^^

.. code-block:: fortran

   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
^^^^^^^^^^^^^^^^^^^

.. code-block:: fortran

   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:

.. code-block:: c

   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
------

.. include:: ./ERRORS.rst