SYNTAX
C Syntax
#include <mpi.h> int MPI_Bsend(const void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm)
Fortran Syntax
INCLUDE 'mpif.h' MPI_BSEND(BUF, COUNT,DATATYPE, DEST, TAG, COMM, IERROR) <type> BUF(*) INTEGER COUNT, DATATYPE, DEST, TAG, COMM, IERROR
C++ Syntax
#include <mpi.h> void Comm::Bsend(const void* buf, int count, const Datatype& datatype, int dest, int tag) const
INPUT PARAMETERS
- buf
- Initial address of send buffer (choice).
- count
- Number of entries 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).
OUTPUT PARAMETER
- IERROR
-
Fortran only: Error status (integer).
DESCRIPTION
MPI_Bsend performs a buffered-mode, blocking send.
NOTES
This send is provided as a convenience function; it allows the user to send messages without worrying 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.)
ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.