sem.rb

#require 'mruby-thread'

m = Mutex.new
v = "foo"
th = Thread.new(v, m) do |v, m|
  for num in 1..3 do
    m.synchronize do
      print("thread: num = ", num, "\n")
      m.unlock
    end
    Thread.sleep 1
  end
  nil
end
for num in 1..3 do
  m.synchronize do
    print("main: num = ", num, "\n")
  end
  Thread.sleep 1
end
th.join