How to NOT interpolate on remote worker?

Usage
, ,
#1 
julia> using Distributed

julia> addprocs(2);

julia> @everywhere a = [1,2]

julia> @everywhere println(a)
[1, 2]
      From worker 3:    [1, 2]
      From worker 2:    [1, 2]

julia> a = 5
5

julia> @everywhere println(a)
5
      From worker 2:    [1, 2]
      From worker 3:    [1, 2]

julia> @fetchfrom 3 a[2]
ERROR: On worker 3:
BoundsError
Stacktrace:

julia> @everywhere println(a)
5
      From worker 2:    [1, 2]
      From worker 3:    5

this above behavior is weird, how do I access the a on the remote?

My real use case is if I have a @distributed for loop, how can I ask Julia NOT to use my local (main process) variable in the body of the loop?

1 Like
Exploiting parallel Julia's auto-global shipping from inside functions and other submodules?
#2

for my second question, it seems to be a scoping problem:

as long as X does not exist in my main process, the loop body will use the remote variable correctly

#3

Sounds like you got it figured out, but in case its useful, this is the relevant section, and @everywhere println(a) is indeed the correct way to access the value of the global variable a on the worker without triggering an auto-send from a on the local process (conversely, @fetchfrom 3 a[2] triggered the auto-send, hence why it ended up being 5 on that worker).

1 Like
#4

The other thing you can do is “hide” accessing the global from the auto-shipping mechanism (and hence prevent auto-sending it) inside an @eval, e.g.

@fetchfrom 3 @eval a[2]

will not send a, it’ll return the global a[2] exactly as it currently exists on the worker.

1 Like