[julia-users] Re: Still confused about how to use pmap with sharedarrays in Julia

[Graydon Barz]

Thank your for the suggestions as they enabled me to solve the issue - 
though for a different reason than I thought.

I had seen indeed seen the StackArray post you mentioned, but my initial 
attempt based on that post did not work. Specifically, following that post, 
I had tried:

output = pmap((x,y) -> f(x, y), ["strg1", "strg2", "strg_3"] , [S,S,S])

and received an error message for each of the three components of the 
output starting with: 
RemoteException(pid#,CapituredException(MethodError(getindex,(0.000115947...  


However, modifying it per your suggestion by defining SVector= fill(S, 3) 
and then running

output = pmap((x,y)->f(x,y), ["strg1", "strg2", "strg3"] , SVector) 

worked.

The fact that meaning of  "," changes depending on what is in placed in 
[a,b,c] seems have been the source of the issue.

(As an aside, this inconsistency seems to me to be somewhat of a 
less-than-desireable feature in Julia.)

On Wednesday, August 10, 2016 at 9:03:03 PM UTC-4, Greg Plowman wrote:
>
> I have also found the combination of shared arrays, anonymous functions 
> and parallel constructs confusing.
>
> StackOverflow question helped me Shared array usage in Julia 
> 
>
> In essence, "although the underlying data is shared to all workers, the 
> declaration is not. You will still need to pass in the reference to [the 
> shared array]"
>
> S = SharedArray(Int,3,4)
> S[:] = 1:length(S)
> @everywhere f(S,i) = (println("S[$i] = $(S[i])"); S[i])
>
> output1 = pmap(i -> f(S,i), 1:length(S))# error
> output2 = pmap((S,i) -> f(S,i), fill(S,length(S)), 1:length(S))
> output3 = pmap(f, fill(S,length(S)), 1:length(S))
>
>
> In seems then, in version1, the reference S is local to the worker, but S 
> is not defined on the worker -> error.
> In versions 2&3 the local S is passed as argument to worker and all works 
> as expected.
>
>

[julia-users] Still confused about how to use pmap with sharedarrays in Julia

[Graydon Barz]

What is the best way to modify the following Julia code:

my_output = pmap(x -> my_function(x, my_shared_array), x_list)

so that 'output' is consistent with 

my_output = map(x -> my_function(x, myarray), x_list)?

My naive attempt above resulted in a an error:  
RemoteException(pid#, CapturedException(UndefVarError: 
my_shared_array),...  which I understand from other posts is because the 
other processes do not know of my_shared_array.

However, attempts to use various permutations of @sync @async have resulted 
in output = Task (done) @x0007 etc., and not the desired 'output' list.