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