Julia 1.0 Example of @distributed and pmap

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1

I am unable to get @distributed (aka @parallel) to work, even with a trivial example. I get errors. is it obvious what I am doing wrong?

$ julia
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.0.0 (2018-08-08)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> using Distributed

julia> @everywhere testrun()= 0

julia> @sync @distributed for i=1:100; testrun(); end
Task (done) @0x000000011d410fd0

julia> addprocs(3)
3-element Array{Int64,1}:
 2
 3
 4

julia> @sync @distributed for i=1:100; testrun(); end
ERROR: On worker 4:
UndefVarError: #testrun not defined
deserialize_datatype at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:1051
handle_deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:743
deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:703
handle_deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:750
deserialize_global_from_main at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:703
#5 at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/clusterserialize.jl:72 [inlined]
foreach at ./abstractarray.jl:1835
deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/clusterserialize.jl:72
handle_deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:797
deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:703
handle_deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:747
deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:703
deserialize_datatype at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:1075
handle_deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:743
deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:703
handle_deserialize at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:750
deserialize_msg at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Serialization/src/Serialization.jl:703
#invokelatest#1 at ./essentials.jl:686 [inlined]
invokelatest at ./essentials.jl:685 [inlined]
message_handler_loop at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/process_messages.jl:160
process_tcp_streams at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/process_messages.jl:117
#105 at ./task.jl:259
#remotecall_fetch#149(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Function, ::Function, ::Distributed.Worker, ::Distributed.RRID, ::Vararg{Any,N} where N) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/remotecall.jl:379
remotecall_fetch(::Function, ::Distributed.Worker, ::Distributed.RRID, ::Vararg{Any,N} where N) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/remotecall.jl:371
#remotecall_fetch#152(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Function, ::Function, ::Int64, ::Distributed.RRID, ::Vararg{Any,N} where N) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/remotecall.jl:392
remotecall_fetch at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/remotecall.jl:392 [inlined]
call_on_owner at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/remotecall.jl:465 [inlined]
wait(::Future) at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/remotecall.jl:486
sync_end(::Array{Any,1}) at ./task.jl:213
macro expansion at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/macros.jl:268 [inlined]
(::getfield(Distributed, Symbol("##169#171")){getfield(Main, Symbol("##7#8")),UnitRange{Int64}})() at ./task.jl:244
Stacktrace:
 [1] sync_end(::Array{Any,1}) at ./task.jl:226
 [2] top-level scope at /Users/osx/buildbot/slave/package_osx64/build/usr/share/julia/stdlib/v1.0/Distributed/src/macros.jl:337
 [3] top-level scope at task.jl:244

pmap() seems to have similar errors. but has the @everywhere not sent off the function to the worker processes?

2

Your issue is that @everywhere defines testrun on every process that is currently running, but processes that are added later do not have testrun defined. If you addprocs(3) before you define testrun (or start julia with julia -p3), then it should work.

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