MPI_Bsend

Basic send with user-specified buffering

Synopsis

#include "mpi.h"
int MPI_Bsend( buf, count, datatype, dest, tag, comm )
void             *buf;
int              count, dest, tag;
MPI_Datatype     datatype;
MPI_Comm         comm;

Input Parameters

	buf	initial address of send buffer (choice)
	count	number of elements 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)

Notes

This send is provided as a convenience function; it allows the user to send messages without worring 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.)

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

MPI_SUCCESS

No error; MPI routine completed successfully.

MPI_ERR_COMM

Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).

MPI_ERR_COUNT

Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.

MPI_ERR_TYPE

Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).

MPI_ERR_RANK

Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.

MPI_ERR_TAG

Invalid tag argument. Tags must be non-negative; tags in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_TAG. The largest tag value is available through the the attribute MPI_TAG_UB.

See Also

MPI_Buffer_attach, MPI_Ibsend, MPI_Bsend_init

Location:bsend.c