# Remote SharedArray problems
**URL:** https://discourse.julialang.org/t/remote-sharedarray-problems/4579
**Category:** General Usage
**Tags:** parallel, cluster
**Created:** [July 1, 2017, 6:27am UTC](https://discourse.julialang.org/t/remote-sharedarray-problems/4579 "2017-07-01T06:27:21Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@alha02](https://discourse.julialang.org/u/alha02)
#### Post date: [July 1, 2017, 6:27am UTC](https://discourse.julialang.org/t/remote-sharedarray-problems/4579/1 "2017-07-01T06:27:21Z")
I am trying to run [this](https://github.com/JuliaLang/julia/issues/13802#issuecomment-152080374) example but I get the following:
```julia
julia> remotes = addprocs([("user@remote_host", 4)])
4-element Array{Int64,1}:
2
3
4
5
julia> S = SharedArray{Int}((3,4), init = S -> S[localindexes(S)] = myid(), pids=remotes)
3×4 SharedArray{Int64,2}:
2 3 4 5
2 3 4 5
2 3 4 5
julia> procs(S)
4-element Array{Int64,1}:
2
3
4
5
julia> r = @spawnat remotes[1] S*eye(4)
ERROR: BoundsError: attempt to access 0×0 Array{Int64,2} at index [1]
Stacktrace:
[1] hash(::SharedArray{Int64,2}, ::UInt64) at ./abstractarray.jl:1950
[2] hash(::SharedArray{Int64,2}) at ./hashing.jl:5
[3] serialize_global_from_main(::Base.Distributed.ClusterSerializer{TCPSocket}, ::Symbol) at ./distributed/clusterserialize.jl:145
[4] foreach(::Base.Distributed.##4#6{Base.Distributed.ClusterSerializer{TCPSocket}}, ::Array{Symbol,1}) at ./abstractarray.jl:1731
[5] serialize(::Base.Distributed.ClusterSerializer{TCPSocket}, ::TypeName) at ./distributed/clusterserialize.jl:83
[6] serialize_type_data(::Base.Distributed.ClusterSerializer{TCPSocket}, ::DataType) at ./serialize.jl:511
[7] serialize_type(::Base.Distributed.ClusterSerializer{TCPSocket}, ::DataType, ::Bool) at ./serialize.jl:554
[8] serialize_any(::Base.Distributed.ClusterSerializer{TCPSocket}, ::Any) at ./serialize.jl:615
[9] serialize_msg(::Base.Distributed.ClusterSerializer{TCPSocket}, ::Base.Distributed.CallMsg{:call}) at ./distributed/messages.jl:89
[10] send_msg_(::Base.Distributed.Worker, ::Base.Distributed.MsgHeader, ::Base.Distributed.CallMsg{:call}, ::Bool) at ./distributed/messages.jl:181
[11] #remotecall#138 at ./distributed/remotecall.jl:325 [inlined]
[12] remotecall(::Function, ::Base.Distributed.Worker) at ./distributed/remotecall.jl:324
[13] #remotecall#139(::Array{Any,1}, ::Function, ::Function, ::Int64) at ./distributed/remotecall.jl:336
[14] spawnat(::Int64, ::Function) at ./distributed/macros.jl:15
```
What am I doing wrong here?
---
### Author:  [@greg\_plowman](https://discourse.julialang.org/u/greg_plowman)
#### Post date: [July 1, 2017, 7:07am UTC](https://discourse.julialang.org/t/remote-sharedarray-problems/4579/2 "2017-07-01T07:07:55Z")
`SharedArray` means shared memory array, and is typically used when workers are on the same machine with access to shared memory.
If you’re trying this on a remote machine, it’s unlikely the machines share memory, and so it’s not going to work.
[https://docs.julialang.org/en/stable/manual/parallel-computing/#man-shared-arrays-1](https://docs.julialang.org/en/stable/manual/parallel-computing/#man-shared-arrays-1)
Depending on your use case, you might look at Distributed Arrays: [https://github.com/JuliaParallel/DistributedArrays.jl](https://github.com/JuliaParallel/DistributedArrays.jl)
---
### Author:  [@alha02](https://discourse.julialang.org/u/alha02)
#### Post date: [July 1, 2017, 7:39am UTC](https://discourse.julialang.org/t/remote-sharedarray-problems/4579/3 "2017-07-01T07:39:33Z")
Well sure, but I am not trying to have a SharedArray shared between different machines. I am trying to have a SharedArray with shared memory on the same machine, but one which is remote. Reading the example in the link I provided it seems that this should be possible to do. In particular:
“I take it your suggestion means that the SharedArray code is designed to be invoked from the master process…”
“The previous invocation, while a bit inefficient should have worked too.”
I interpret this that it should be perfectly ok to construct a SharedArray with a call on a local process, where the array will live on a remote machine, as long as all the pids in the call are on that same remote machine. I mean I am basically only calling the commands provided by Amit Murthy, who seems to be one of the main contributors to DistributedArrays.jl and parallel Julia in general.
---
### Author:  [@greg\_plowman](https://discourse.julialang.org/u/greg_plowman)
#### Post date: [July 3, 2017, 2:14am UTC](https://discourse.julialang.org/t/remote-sharedarray-problems/4579/4 "2017-07-03T02:14:36Z")
Ah, I can see what you’re trying to do now.
I can confirm that for me, this works on v0.5.1, but not on v0.6.0. Seems like a regression.
Error message suggests that serialize is trying to hash the shared array locally - same error as trying to access S locally, say by executing `S[1]`.
Maybe worth raising an issue?
---
### Author:  [@alha02](https://discourse.julialang.org/u/alha02)
#### Post date: [July 4, 2017, 4:57pm UTC](https://discourse.julialang.org/t/remote-sharedarray-problems/4579/5 "2017-07-04T16:57:54Z")
Yes, seems like it is actually a bug then. Thanks for confirming!