NAME¶

MPI_Buffer_attach - Attaches a user-defined buffer for sending.

SYNTAX¶

C Syntax¶

#include <mpi.h>
int MPI_Buffer_attach(void  *buf, int size)

Fortran Syntax¶

INCLUDE 'mpif.h'
MPI_BUFFER_ATTACH( BUF, SIZE, IERROR)
	<type>	 BUF(*)
	INTEGER	 SIZE, IERROR 

C++ Syntax¶

#include <mpi.h>
void Attach_buffer(void*  buffer, int size)

INPUT PARAMETERS¶

buf

Initial buffer address (choice).

size

Buffer size, in bytes (integer).

 

OUTPUT PARAMETER¶

IERROR

Fortran only: Error status (integer).

 

DESCRIPTION¶

Provides to MPI a buffer in the user's memory to be used for buffering outgoing messages. The buffer is used only by messages sent in buffered mode. Only one buffer can be attached to a process at a time.

NOTES¶

The size given should be the sum of the sizes of all outstanding Bsends that you intend to have, plus MPI_BSEND_OVERHEAD bytes for each Bsend that you do. For the purposes of calculating size, you should use MPI_Pack_size. In other words, in the code

    MPI_Buffer_attach( buf, size );
    MPI_Bsend( ..., count=20, datatype=type1, ... );
    ...
    MPI_Bsend( ..., count=40, datatype=type2, ... );

the value of size in the MPI_Buffer_attach call should be greater than the value computed by

    MPI_Pack_size( 20, type1, comm, &s1 );
    MPI_Pack_size( 40, type2, comm, &s2 );
    size = s1 + s2 + 2 * MPI_BSEND_OVERHEAD;

MPI_BSEND_OVERHEAD gives the maximum amount of buffer space that may be used by the Bsend routines. This value is in mpi.h for C and mpif.h for Fortran.

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.

SEE ALSO¶

MPI_Buffer_detach