montecarlo.rb

#!/usr/bin/ruby
require 'drb/drb'
class MonteCarlo
  def initialize(seed)
    srand(seed)
  end
  def dice(n)
    best = rand
    n.times do
      r = rand
      best = r if r < best
    end
    best
  end
end

PROCESSORS = (ARGV[0] || 1).to_i

pids = []
foos = PROCESSORS.times.map do |i|
  uri = "druby://localhost:#{12345 + i}"
  pids << fork { DRb.start_service(uri, MonteCarlo.new(i)); sleep }
  DRbObject.new_with_uri(uri)
end

begin
  n = 5000000 / PROCESSORS
  q = Queue.new
  sleep 0.1
  ts = foos.map do |foo|
    Thread.start(foo) {|f| q.push(f.dice(n))}
  end
  ts.each{|t| t.join}
  p q.size.times.map{q.pop}.min
ensure
  pids.each {|pid| Process.kill(:TERM, pid)}
end

# ruby1.8.7
#
# PS CoreDuo Core i7
# ------------------------
#  1 7.284s  4.482s
#  2 3.882s  2.120s
#  3 3.898s  1.417s
#  4 3.876s  1.102s
#  5 3.695s  1.163s
#  6 3.754s  0.997s
#  7 3.716s  0.958s
#  8 3.666s  0.974s
#  9 3.738s  1.029s
# 10 3.713s  0.983s
# 11 3.905s  0.981s
# 12 3.776s  0.952s
# 13 3.697s  0.934s
# ..
# 18 3.816s  0.896s
# ..
# 32 3.669s  0.907s
# ..
# 64 4.036s  0.942s
# ..
# 96 4.643s  0.973s

# ruby1.9.1
#
# PS CoreDuo Core i7
# ------------------------
#  1 4.675s  2.082s
#  2 2.677s  1.112s
#  3 2.656s  0.791s
#  4 2.609s  0.625s
#  5 2.746s  0.705s
#  6 2.649s  0.656s
#  7 2.581s  0.641s
#  8 2.626s  0.616s
#  9 2.691s  0.646s
# 10 2.617s  0.632s
# 11 2.619s  0.629s
# 12 2.573s  0.633s
# ..
# 16 2.705s  0.639s
# ..
# 32 2.619s  0.662s
# ..
# 64 3.144s  0.625s
# ..
# 96 3.010s  0.797s