NonblockingChannel

Example: Nonblocking Channel:

    import stackless

    class NonblockingChannel(stackless.channel):
        def send(self, value, wait=False):
            if wait or self.balance < 0: 
                # there are tasklets waiting to receive
                return stackless.channel.send(self, value)
        def send_exception(self, exc, value, wait=False):
            if wait or self.balance < 0: 
                # there are tasklets waiting to receive
                return stackless.channel.send_exception(self, exc, value)
        def receive(self, default=None, wait=False):
            if wait or self.balance > 0:
                # there are tasklets waiting to send
                return stackless.channel.receive(self)
            else:
                return default

    def testNonblockingChannel():
        print
        print "testNonblockingChannel"
        print "----------------------"

        def recv(ch, name):
            print "Started recv<%s>" % (name,)
            print "recv<%s>: got a message from \\"%s\\"" % (name, ch.receive(wait=True))
            ch.send(name)

        ch = NonblockingChannel()
        ch.receive() # nonblocking receive
        ch.send("nonblocking!") # nonblocking send

        for name in "ABCDE":
            task = stackless.tasklet(recv)(ch, name)
            task.run()

        ch.send('host')
        print

testNonblockingChannel() should print:

    testNonblockingChannel
    ----------------------
    Started recv<A>
    Started recv<B>
    Started recv<C>
    Started recv<D>
    Started recv<E>
    recv<A>: got a message from "host"
    recv<B>: got a message from "A"
    recv<C>: got a message from "B"
    recv<D>: got a message from "C"
    recv<E>: got a message from "D"