gistfile1.rb

require 'thread'

input   = [10, 12, 14, 18]
output  = []
threads = []
lock    = Mutex.new

def fib(n)
  return n < 2 ? n : fib(n-1) + fib(n-2)
end

10.times do |index|
  threads << Thread.new do
    input.each do |some_value|
      lock.synchronize { output << fib(some_value) }
    end
  end
end

threads.each(&:join)

p output