MPI_Bsend(3)

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

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.

SEE ALSO
MPI_Buffer_attach
MPI_Ibsend
MPI_Bsend_init