[Mpi3-rma] Alternative Proposal for Shared Memory Support

[Torsten Hoefler]

On Tue, Mar 15, 2011 at 09:39:24PM -0500, Rajeev Thakur wrote:
> That's what I meant in my first mail. We need to say whether this example will work or not.
> 
> A=10
> barrier         barrier
>                     x = A
> 
> If not, which synchronization functions need to be used and how? The
> current text does not automatically cover this example.
Right, I never claimed that the proposal is complete :-). It's basically
a quick poll to see if there are major flaws and I should retract or if
it is worth discussing at the Forum (to flesh out such things like you
mentioned).

To answer your question: I think this should either be:

A=10
MPI_Win_flush
barrier           barrier
                  x=A

This would basically insert a membar in MPI_Win_flush which makes
sure that A is committed before the barrier completes (a barrier flag is
set and read).

This fits our current semantics where we suggest that win_flush can be
used for ordering. Keep in mind that it's still the unified model, i.e.,
the value would commit eventually, the flush is just needed to enforce
ordering with regards to the barrier.

Thanks & Best,
  Torsten

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