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