[Mpi3-rma] nonblocking MPI_Win_create etc.?

Jeff Hammond jhammond at alcf.anl.gov
Thu Sep 22 16:25:28 CDT 2011

I work with someone who has a use case for nonblocking window creation
because can get into a deadlock situation unless he does a lot of
bookkeeping.  He's creating windows on subgroups of world that can
(will) overlap.  In order to prevent deadlock, he will have to do a
global collective and figure out how to order all of the window
creation calls so that they do not deadlock, or in the case where that
requires solving an NP-hard problem (it smells like the scheduling
problem to me) or requires too much storage to be practical (he works
at Juelich and regularly runs on 72 racks in VN mode), he will have to
serialize window creation globally.

Nonblocking window creation and a waitall solves this problem.

Thoughts?  I wonder if the semantics of nonblocking collectives -
which do not have tags - are even sufficient in the general case.


Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381

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