gistfile1.rb

require 'java'

java_import java.util.concurrent.Executors
java_import java.util.concurrent.Callable
java_import java.lang.Runtime
java_import java.lang.System

$cores = Runtime.getRuntime.availableProcessors
queue = Executors.newFixedThreadPool($cores)

def benchmark(&work)
  before = System.nanoTime
  3.times { work.call }
  after = System.nanoTime

  p "That took #{(after - before)/1E9}s"
end


class Task
  include Callable

  def initialize(&block)
    @work = block
  end

  def call
    @work.call
  end
  
end

class Array
  def pmap(executor, &block)
    # Parcel out the work into chunks to be executed sequentially
    tasks = self.each_slice(self.size / $cores).map do |slice|
      Task.new { slice.map {|i| block.call(i) } }
    end

    # Execute them all, block until they're done
    results = executor.invokeAll(tasks)

    # Dereference and merge all the FutureTasks
    results.reduce([]) { |memo,obj| memo + obj.get }
  end
end


a = (0..1E6).to_a

p 'Splendid new Array#pmap'
benchmark { a.pmap(queue) { |i| i += 1 } }

p 'Plain old sequential Array#map'
benchmark { a.map { |i| i += 1 } }



queue.shutdown