gistfile1.rb

a = ""

func1 = Proc.new do
  i = 0
  while i <= 100
    puts "func1 "
    sleep(0.001)
    a.concat "aaaa"
    i = i + 1
  end
end
func2 = Proc.new do
  i = 0
  while i <= 100
    puts "func2 "
    sleep(0.001)
    a.concat "bbbb"
    i = i + 1
  end
end

puts "Start at: #{Time.now}"
t1 = Thread.new{func1.call}
t2 = Thread.new{func2.call}
t1.join
t2.join
puts "a is #{a}"
puts "End at: #{Time.now}"