bionic (3) MPI_Buffer_detach.3.gz

NAME

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

SYNOPSIS

       int MPI_Buffer_detach(void *buffer_addr, int *size)

OUTPUT PARAMETERS

       buffer_addr
              - initial buffer address (choice)
       size   - buffer size, in bytes (integer)

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  is  simple)  and
       weaknesses (it only works for nested usages).

       Note  that  for  this  approach  to work, MPI_Buffer_detach must return MPI_SUCCESS even when there is no
       buffer to detach.  In that case, it returns a size of zero.  The MPI 1.1 standard  for  MPI_BUFFER_DETACH
       contains the text

       The statements made in this section describe the behavior of MPI for
       buffered-mode sends. When no buffer is currently associated, MPI behaves
       as if a zero-sized buffer is associated with the process.

       This  could  be  read  as  applying  only  to  the various Bsend routines.  This implementation takes the
       position that this applies to MPI_BUFFER_DETACH as well.

THREAD AND INTERRUPT SAFETY

       The user is responsible for ensuring that multiple threads do not try to update the same MPI object  from
       different threads.  This routine should not be used from within a signal handler.

       The  MPI  standard defined a thread-safe interface but this does not mean that all routines may be called
       without any thread locks.  For example, two threads must not attempt to change the contents of  the  same
       MPI_Info  object  concurrently.   The  user is responsible in this case for using some mechanism, such as
       thread locks, to ensure that only one thread at a time makes use of this routine.  Because the buffer for
       buffered  sends  (e.g.,  MPI_Bsend  )  is shared by all threads in a process, the user is responsible for
       ensuring that only one thread at a time calls this routine or MPI_Buffer_attach .

NOTES FOR FORTRAN

       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the
       end of the argument list.  ierr is an integer and has the same meaning as the return value of the routine
       in C.  In Fortran, MPI routines are subroutines, and are invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in 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.

NOTES FOR C

       Even though the bufferptr argument is declared as void * , it is really the address of  a  void  pointer.
       See the rationale in the standard for more details.

SEE ALSO

       MPI_Buffer_attach

                                                   11/12/2016                               MPI_Buffer_detach(3)