MPI_Bsend
Basic send with user-specified buffering
Synopsis
int MPI_Bsend(void *buf, int count, MPI_Datatype datatype, 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)
- 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_Comm_set_errhandler (for communicators),
MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for
RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but
its use is deprecatd. 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; however, MPI implementations will attempt to continue whenever
possible.
- 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