Hi Christoph, Thanks for the updates. I think this is the correct solution. In short, a=a+1 is not atomic. You have to use an atomic operation in your case, thus it needs to be MPI_ACCUMULATE. Min On 6/21/16 4:04 AM, C.Friedrich wrote:

Thank you.

After some research I have been able to solve the problem: MPI_WIN_FENCE is correct, but an assignment like a=a+1 will always lead to race conditions. This assignment has to be replaced by calls to MPI_ACCUMULATE, which is "atomic" by design. So, calls to MPI_ACCUMULATEs do not have to be separated by "fences". However, we need fences to separate them from the local store (a=0) before and from the read (e.g., write(*,*) a) afterwards. In the present case, one could write

... b=1 tdisp=0 call mpe_win_fence(a,0,Nwin,err) do i = 1,10000 call mpi_accumulate(b,100,mpi_integer,0,tdisp,100,mpi_integer,mpi_sum,Nwin,err)

enddo call mpe_win_fence(a,0,Nwin,err) ...

Christoph

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