MPI_Buffer_detach(3OpenMPI)											       MPI_Buffer_detach(3OpenMPI)

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 dif-
       ferently: 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++ func-
       tions 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

Open MPI 1.2							  September 2006				       MPI_Buffer_detach(3OpenMPI)