Answer to a recent LRUG question about downloading of images in parallel. I noticed everyone seemed to shy away from threads, but with j.u.c you get a lot for free including battle hardened concurrency semantics.

gistfile1.rb

#!/usr/bin/env jruby
java_import java.util.concurrent.Executors

require 'net/http'

class ThreadedDownloader

	def initialize(poolsize = 50)
		@executor = Executors.new_fixed_thread_pool(poolsize)
	end

	def download(file_list = [])
		file_list.each {|f| download_file(f)}
		@executor.shutdown if @executor
	end

	def download_file(src, dest = nil)
		@executor.submit do
			uri = URI(src)
			Net::HTTP.start(uri.host) do |http|
			resp = http.get(uri.path)
				dest = dest.nil? ? File.basename(uri.path) : dest
				open(dest, "wb") do |file|
				file.write(resp.body)
					puts "Downloaded #{dest}"
				end
			end
		end
	end
end

files = [
	"http://www.cedmagic.com/featured/he-man/he-man.jpg",
	"http://images1.wikia.nocookie.net/__cb20090716165928/heman/images/c/c3/Heman83.jpg",
	"http://geektyrant.com/storage/0999-post-images/heman7162012.jpeg?__SQUARESPACE_CACHEVERSION=1342543799392",
	"http://www.dvdactive.com/images/reviews/screenshot/2004/8/heman3_copy0.jpg",
	"http://media.comicvine.com/uploads/9/98086/1888897-superman_flying.jpg"
]

ThreadedDownloader.new.download(files)