reentrant_mutex.rb

class ReentrantMutex < Mutex

  def initialize
    super
    @locker = nil
  end

  alias :original_synchronize :synchronize

  def synchronize
    if @locker == Thread.current
      yield
    else
      original_synchronize {
        begin
          @locker = Thread.current
          yield
        ensure
          @locker = nil
        end
      }
    end
  end
end  # class ReentrantMutex