Return and args

[mloubout]

I don't know if I missed somethign but I can't seem to fund a way to return value for the " only workers execute MPI code" mode. While the example seemed exciting, I can't seem to find a way to do a simple (pseudo code)

function do_stuff(args)
        manager=MPIManager(np=np)
        workers = addprocs(manager)
        @mpi_do manager begin
             result = do_mpi_stuff($args)
             result = gather_on_root(results)
             if comm is root
                  return result
            end
       end
end

myresult = do_stuff(a,b,c)

which makes it a bit useless since I can't get a result back.

[aitzkora]

May be modyfing a little bit the function mpi_do for returning the args, will do the job

function mpi_callfetch(mgr::MPIManager, expr)
    !mgr.initialized && wait(mgr.cond_initialized)
    jpids = keys(mgr.j2mpi)
    refs = Array{Any}(undef, length(jpids))
    for (i,p) in enumerate(Iterators.filter(x -> x != myid(), jpids))
        refs[i] = remotecall(expr, p)
    end
    # Execution on local process should be last, since it can block the main
    # event loop
    if myid() in jpids
        refs[end] = remotecall(expr, myid())
    end

    # Retrieve remote exceptions if any
    @sync begin
        for r in refs
            @async begin
                resp = remotecall_fetch(r.where, r) do rr
                    wrkr_result = rr[]
                end
                isa(resp, Exception) && throw(resp)
            end
        end
    end
    wrkr_result
end

When I have time, I will fork to test that solution. it is a copy-paste of mpi_do function where we do not filter the remote_callfetch results. Authors of the package say that @mpi_do is not a mpi_callfetch (it is logical, "do" in the name explicits it is a void function),
so I agree with you that it would be nice to have such macros in that package...

[mloubout]

I ended up making an mpicall_fetch locally indeed. I had to bypass kill as well that doesn't play well with my code in a may that is not reliable for this package (I had to remove the MPI.Finilazie() because it's called already by some other code).
I may PR the mpicall_fetch here to make it cleaner.
Thanks for your response.

[aitzkora]

Nice ! I hope authors will accept your PR. I'm currently writing a poster for Julia Con advocating for @mpi_do, but having also a @mpicall_fetch would be great.
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