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 ------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------ Forschungszentrum Juelich GmbH 52425 Juelich Sitz der Gesellschaft: Juelich Eingetragen im Handelsregister des Amtsgerichts Dueren Nr. HR B 3498 Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher Geschaeftsfuehrung: Prof. Dr.-Ing. Wolfgang Marquardt (Vorsitzender), Karsten Beneke (stellv. Vorsitzender), Prof. Dr.-Ing. Harald Bolt, Prof. Dr. Sebastian M. Schmidt ------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------ _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss