NAME

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

C++ Syntax

#include <mpi.h>
void Comm::Bsend(const void* buf, int count, const
	Datatype& datatype, int dest, int tag) const

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 PARAMETER

IERROR: Fortran only: Error status (integer).

DESCRIPTION

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 MPI_Buffer_attach).

In deciding how much buffer space to allocate, remember that the buffer space is not available for reuse by subsequent MPI_Bsends 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

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; 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.