new_contents: from eventlet import coros
  
  class channel(coros.queue):
  
      def __init__(self):
          coros.queue.__init__(self, 0)
  
      def receive(self):
          return self.wait()
  
      @property
      def balance(self):
          return self.sem.balance
  
  
  
subject: add channel.channel based on coros.queue(0) (temporarily for backward compatibility)