import stackless

class MyChannel:
    def __init__(self):
        self.queue = []
        self.balance = 0
        self.temp = None
    def send(self, data):
        if self.balance < 0:
            receiver = self.queue.pop(0)
            self.temp = data
            receiver.insert()
            self.balance += 1
            receiver.run()
        else:
            sender = stackless.current
            self.queue.append((sender, data))
            self.balance += 1
            jump_off(sender)
    def receive(self):
        if self.balance > 0:
            sender, retval = self.queue.pop(0)
            sender.insert()
            self.balance -= 1
            return retval
        else:
            receiver = stackless.current
            self.queue.append(receiver)
            self.balance -= 1
            jump_off(receiver)
            return self.temp

def jump_off(task):
    stackless.tasklet().capture()
    task.remove()
    stackless.schedule()

def f1(ch):
    for i in range(5):
        ch.send(i)
    print "done sending"

def f2(ch):
    while 1:
        data = ch.receive()
        if data is None:
            print "done receiving"
            return
        print "received", data

def test():
    ch = MyChannel()
    t2 = stackless.tasklet(f2)(ch)
    t1 = stackless.tasklet(f1)(ch)
    stackless.run()
    return ch

if __name__=="__main__":
    test()