NAME¶

MPI_Bsend - Basic send with user-specified buffering

SYNOPSIS¶

#include <mpi.h>
int MPI_Bsend(void *buf, int count, MPI_Datatype dtype, 


              int dest, int tag, MPI_Comm comm)

INPUT PARAMETERS¶

buf

- initial address of send buffer (choice)

count

- number of elements in send buffer (nonnegative integer)

dtype

- 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_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.)

It is generally a bad idea to use the MPI_Bsend function, as it guarantees that the entire message will suffer the overhead of an additional memory copy. For large messages, or when shared memory message transports are being used, this overhead can be quite expensive.

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¶

If an error occurs in an MPI function, the current MPI error handler is called to handle it. 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 (in C and Fortran; this error handler is less useful in with the C++ MPI bindings. The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value needs to be recovered). Note that MPI does not guarantee that an MPI program can continue past an error.

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. The C++ bindings for MPI do not return error values; instead, error values are communicated by throwing exceptions of type MPI::Exception (but not by default). Exceptions are only thrown if the error value is not MPI::SUCCESS .

Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return upon an error, there will be no way to recover what the actual error value was.

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_Buffer_detach, MPI_Ibsend, MPI_Bsend_init

MORE INFORMATION¶

For more information, please see the official MPI Forum web site, which contains the text of both the MPI-1 and MPI-2 standards. These documents contain detailed information about each MPI function (most of which is not duplicated in these man pages).

http://www.mpi-forum.org/

ACKNOWLEDGEMENTS¶

The LAM Team would like the thank the MPICH Team for the handy program to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial formatting, and some initial text for most of the MPI-1 man pages.

LOCATION¶

bsend.c