Improve Documentation on SharedArrays #13922
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ahwillia opened this Issue on Nov 8, 2015 · 1 comment
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@ahwillia
ahwillia commented on Nov 8, 2015

Caveat -- I'm new to using the parallel tools in Julia, but I think this section of the documentation could use some love: http://julia.readthedocs.org/en/latest/manual/parallel-computing/#parallel-map-and-loops

In particular, it notes that the following won't work as intended:

a = zeros(10)
@parallel for i=1:10
  a[i] = i
end

But states that Distributed Arrays can fix this. It doesn't provide any specifics though. Simply trying:

using DistributedArrays
a = dzeros(10)
@parallel for i=1:10
  a[i] = i
end

Doesn't produce the desired behavior either. Neither does @everywhere using DistributedArrays. However, using SharedArrays does work:

a = SharedArray(Float64,10)
@parallel for i=1:10
  a[i] = i
end

If there is a way to make something simple like this work with DistributedArrays, I think it would be nice to include an example.

I've also seen people use @sync @parallel for i=1:10... but this doesn't seem necessary to get the desired behavior. Happy to contribute to the documentation if this sounds reasonable.
@tkelman tkelman added the doc label on Nov 8, 2015
@timholy
The Julia Language member
timholy commented on Nov 8, 2015

Certainly doc improvements would be very welcome. It sounds like a minimalist improvement would be directing users to SharedArrays rather than DistributedArrays.

As for a good illustration of DistributedArrays, I haven't used them in ages so I can't offer any useful advice. But surely there are others who can. I trust you've check the docs at https://github.com/JuliaParallel/DistributedArrays.jl?
@kshyatt kshyatt added the parallel label on Nov 9, 2015
@ahwillia ahwillia added a commit to ahwillia/julia that referenced this issue on Nov 10, 2015
	@ahwillia 	Add pointer to SharedArrays
			b78cf55
@ahwillia ahwillia referenced this issue on Nov 10, 2015
Merged
Edit Docs: Add pointer to SharedArrays #13937
@ahwillia ahwillia closed this on Nov 17, 2015