[julia-users] Mutual exclusion when writing to SharedArrays?

[John Brock]

I'm seeing inconsistent results when multiple workers write values to a 
SharedArray at the same time, presumably because += isn't atomic. Is this 
intended behavior, and is there a workaround? Behavior is reproducible in 
0.3.8-pre+22 and 0.3.9. 

Sample code:

function doStuff()
  result_shared = SharedArray(Int64, (2,), init = S -> S[localindexes(S)] = 
0)
  @sync for i=1:3
    @spawn begin
      result_shared[:] += [i, i]
    end
  end
  return sdata(result_shared)
end

> julia -p 3

julia> dump(doStuff()) 
Array(Int64,(2,)) [3,3]

julia> dump(doStuff()) 
Array(Int64,(2,)) [6,6]