Groups   16 of 99+      julia-users › SharedArray   parallel question 6 posts by 3 authors      Christopher Alexander    Jan 29   Hello all, I have a question about the proper usage of SharedArray    parallel.  I am trying to use it in a particular part of my code, but I am not getting the expected results  instead I am getting an array of zeros each time .  Here are the two functions that are involved: function partial_rollback! lattice::TreeLattice, asset::DiscretizedAsset, t::Float64    from   asset.common.time    if QuantJulia.Math.is_close from, t      return   end    iFrom   findfirst lattice.tg.times .   from    iTo   findfirst lattice.tg.times .   t      simd for i   iFrom-1:-1:iTo     newVals   step_back lattice, i, asset.common.values       inbounds asset.common.time   lattice.tg.times i      asset.common.values   sdata newVals           if i !  iTo       adjust_values! asset      end   end    return asset end  function step_back lattice::TreeLattice, i::Int, vals::Vector Float64      newVals   SharedArray Float64, get_size lattice.impl, i      parallel for j   1:length newVals      val   0.0     for l   1:lattice.n       val +  probability lattice.impl, i, j, l    vals descendant lattice.impl, i, j, l       end     val    discount lattice.impl, i, j      newVals j    val   end   retArray   sdata newVals       return retArray end  Is that to much complexity in the parallel loop?  Right now the max   of times I've seen over this loop is in the 9000+ range, so that's why I thought it would be better than pmap. Any suggestions?  Thanks!  Chris     Christopher Alexander    Jan 29   I tried using  sync  parallel and ended up getting a segmentation fault, so I'm not really sure how to parallelize this loop.  This is inside of a larger module, so I'm not sure if something special has to be done  e.g. putting  everywhere somewhere .  I've searched this forum and the documentation, which is where I got the idea to add  sync.  I'd appreciate any input, as I'm kind of stuck.  The larger code in which this parallelization should take place is here: https:  github.com pazzo83 QuantJulia-jl blob master src methods lattice-jl  Thanks!  Chris      Lutfullah Tomak    Jan 30   There is this issue on on github https:  github.com JuliaLang julia issues 14764 . I am no expert about parallel computing but may be related. Regards      Christopher Alexander    Jan 30   I can confirm that I do not see the seg fault issue in 0.5  the latest master , but I am getting fundamentally different results when using the  sync  parallel construction.  In essence,  sync  parallel is causing arrays of different values  compared to using a non-parallelized construction  to be built, which is causing an issue further along in my program.  It is also much slower, so I am wondering if I my syntax is incorrect.  Any input would be appreciated.  You can see what is supposed to be generated by loading this script  https:  github.com pazzo83 QuantJulia-jl blob master swaption_test_code-jl  and calling main  .  Thanks!   On Saturday, January 30, 2016 at 4:48:51 AM UTC-5, Lutfullah Tomak wrote: There is this issue on on github https:  github.com JuliaLang julia issues 14764 . I am no expert about parallel computing but may be related. Regards      Christopher Alexander    Jan 31   Is this something that would really only be solved by proper multi-threading?      ele... gmail.com    Jan 31   Are you absolutely sure that, in the part you are trying to parallelize, no computation depends on the results of a previous computation.  If those two computations are moved from serial to parallel then there is no guarantee that the first is complete before the second happens on a different process.   Subtle situations include using the values from cells in an array  other than the one you are about to update .  Those other cells may or may not be updated if the update code is in another process.