Actually, afaik, Win_fence is not the right synchronization method for you approach. As Halim said, you should use 
passive-target synchronization here. Fence guarantees you that  all RMA operations on win originating at a given
process and started before the fence call will complete at that process before the fence call return - so it only
synchronizes RMA calls - but not multiple accesses to the same are. 

However, in you example that does NOT avoid that two processes access a at the same time
- that why you get your race-condition.


Lena 

On Apr 13, 2016, at 3:08 PM, Halim Amer <aamer@anl.gov> wrote:

Win_sync can only be used within passive target epochs. You could replace the win_fences with win_locks.

--Halim

On 4/13/16 11:28 AM, C.Friedrich wrote:
Thanks for the suggestion! Adding MPI_WIN_SYNC in this way:
     do i = 1,10000
       call mpe_win_fence(a,0,Nwin,err)
       a = a + 1
       call mpi_win_sync(Nwin,err)
       call mpe_win_fence(a,0,Nwin,err)
     enddo
does not work. The compiled executable either issues the error
Fatal error in MPI_Win_sync: Wrong synchronization of RMA calls , error
stack:
MPI_Win_sync(115)..: MPI_Win_sync(win=0xa0000000) failed
MPID_Win_sync(1805): Wrong synchronization of RMA calls
or simply dies (without writing the numbers). Perhaps I use it
incorrectly...

Christoph



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