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       MPI_Buffer_attach - Attaches a user-defined buffer for sending.


C Syntax

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

Fortran Syntax

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

C++ Syntax

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


       buf       Initial buffer address (choice).

       size      Buffer size, in bytes (integer).


       IERROR    Fortran only: Error status (integer).


       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.


       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

           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.


       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.