master_slave DArray copy

Hello,

First, thank you for a great package!

I have had an issue with copy of DArray when connected in master_slave topology.

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

julia> nprocs()
3              
julia> using DistributedArrays

julia> dd=drand((11,21,2,13),workers(),[1,1,1,2]);

julia> @eval @everywhere println(localindexes($dd))
(1:0,1:0,1:0,1:0)                                  
        From worker 2:  (1:11,1:21,1:2,1:7)        
        From worker 3:  (1:11,1:21,1:2,8:13)       

julia> ddc=copy(dd);
ERROR: On worker 2: 
peer 3 is not connected to 2. Topology : master_slave                                                                                                   
...

I have shortened the error output, surely you can reproduce it.

Is there a reason why this is an error?

Especially that this works...

julia> dd=drand((11,21,2,13),workers(),[1,1,1,2]);

julia> @everywhere using DistributedArrays

julia> @eval ddc2=DArray(I->copy(localpart($dd)),$dd);

julia> sumabs2(ddc2-dd)
0.0

julia> @eval @everywhere println(localindexes($ddc2))
(1:0,1:0,1:0,1:0)
        From worker 2:  (1:11,1:21,1:2,1:7)
        From worker 3:  (1:11,1:21,1:2,8:13)

julia> @eval @everywhere println(localindexes($dd))
(1:0,1:0,1:0,1:0)
        From worker 3:  (1:11,1:21,1:2,8:13)
        From worker 2:  (1:11,1:21,1:2,1:7)

Finally, is there a reason why similar does not yield a DArray with the same distribution?

julia> dd=drand((11,21,2,13),workers(),[1,1,1,2]);

julia> @eval @everywhere println(localindexes($dd))
(1:0,1:0,1:0,1:0)
        From worker 2:  (1:11,1:21,1:2,1:7)
        From worker 3:  (1:11,1:21,1:2,8:13)

julia> ddc=similar(dd);

julia> @eval @everywhere println(localindexes($ddc))
(1:0,1:0,1:0,1:0)
        From worker 2:  (1:11,1:11,1:2,1:13)
        From worker 3:  (1:11,12:21,1:2,1:13)

I appreciate any help on this, and again thanks for the effort with this package!

Bắt đầu bằng cách tái hiện các ví dụ master_slave bằng DArray, copy, similar và localpart như được trình bày trong issue. Kiểm tra các phần triển khai và test cho DArray copy và similar, sau đó xác minh hành vi bằng các kiểm tra localindexes và sumabs2 được cung cấp. Hoàn thành khi copy và similar xử lý được phân phối đã báo cáo hoặc ghi rõ hành vi dự kiến.