[mpich-discuss] Race condition in MPI3 (Fortran, shared memory)

[C.Friedrich]

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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Forschungszentrum Juelich GmbH
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Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher
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Karsten Beneke (stellv. Vorsitzender), Prof. Dr.-Ing. Harald Bolt,
Prof. Dr. Sebastian M. Schmidt
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