All workers not have access to a sharedarray

New to Julia
, ,
1

Hi,
I get an error that x is not defined on worker 2/others when I run this.

using Distributed
addprocs(4)

@everywhere using SharedArrays

x = zero( SharedArray{Float64}( 10 ) );

@everywhere println( x[2] )

What is wrong here?
Thanks

2

It seems, from the docs, that you have to interpolate x to all procs before using it:

julia> using SharedArrays, Distributed

julia> addprocs(4)
4-element Array{Int64,1}:
 2
 3
 4
 5

julia> x = zero( SharedArray{Float64}( 10 ) );

julia> @everywhere x = $x

julia> @everywhere println( x[5] )
0.0
      From worker 3:	0.0
      From worker 4:	0.0
      From worker 5:	0.0
      From worker 2:	0.0

https://docs.julialang.org/en/v1/stdlib/Distributed/#Distributed.@everywhere

ps. Welcome, and use the ticks indicate the code, it is much better (The </> on the top bar add the correct ticks).

3

Nice, thanks.

However, would that not make extra local copies of x for all workers? If yes, that would be not-so-good use of the memory.

4

I don’t think so. Interpolations are not copies, they mean that an expression is passed instead of the value of the variable. But I am not completely sure of how they work, and the references where not clear. Possibly someone else can improve on this explanation.