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NAME

       MPI_Buffer_detach - Removes an existing buffer (for use in MPI_Bsend, etc.)

SYNTAX

C Syntax

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

Fortran Syntax

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

C++ Syntax

       #include <mpi.h>
       int Detach_buffer(void*& buffer)

OUTPUT PARAMETERS

       buf       Initial buffer address (choice).

       size      Buffer size, in bytes (integer).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       Detach the buffer currently associated with MPI. The call returns the address and the size
       of the detached buffer. This operation will block until  all  messages  currently  in  the
       buffer  have  been  transmitted.  Upon  return  of  this  function,  the user may reuse or
       deallocate the space taken by the buffer.

       Example: Calls to attach and detach buffers.

           #define BUFFSIZE 10000
           int size
           char *buff;
           MPI_Buffer_attach( malloc(BUFFSIZE), BUFFSIZE);
           /* a buffer of 10000 bytes can now be used by MPI_Bsend */
           MPI_Buffer_detach( &buff, &size);
           /* Buffer size reduced to zero */
           MPI_Buffer_attach( buff, size);
           /* Buffer of 10000 bytes available again */

NOTES

       The reason that MPI_Buffer_detach returns  the  address  and  size  of  the  buffer  being
       detached  is  to  allow  nested  libraries to replace and restore the buffer. For example,
       consider

           int size, mysize, idummy;
           void *ptr, *myptr, *dummy;
           MPI_Buffer_detach( &ptr, &size );
           MPI_Buffer_attach( myptr, mysize );
           ...
           ... library code ...
           ...
           MPI_Buffer_detach( &dummy, &idummy );
           MPI_Buffer_attach( ptr, size );

       This is much like the action of the UNIX signal routine and has the same  strengths  (it's
       simple) and weaknesses (it only works for nested usages).

       For  Fortran:  The Fortran binding for this routine is different. Because Fortran does not
       have pointers, it is impossible to provide a way to use the  output  of  this  routine  to
       exchange buffers. In this case, only the size field is set.

       For  C:  Even  though  the buf argument is declared as void, it is really the address of a
       void pointer. See Rationale, below, for more details.

       Even though the C functions MPI_Buffer_attach and  MPI_Buffer_detach  both  have  a  first
       argument  of  type void*, these arguments are used differently: A pointer to the buffer is
       passed to MPI_Buffer_attach; the address of the pointer is passed to MPI_Buffer_detach, so
       that this call can return the pointer value.

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_attach
       MPI_Bsend