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)
- 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
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