MPI_Buffer_detach(3)               Open MPI               MPI_Buffer_detach(3)



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



1.4.1                            Jan 14, 2010             MPI_Buffer_detach(3)
