[Stackless] API suggestions

[Sune Kirkeby]

[ Oren Tirosh ]
> 1. Represent each channel with two separate objects - one for the 
> sender and one of the receiver side. The reference counts of the 
> two objects are tracked separately. This can be useful for debugging: 
> a tasklet will not block on sending to a channel with no receivers 
> or attempting to receive from a channel with no senders. Instead 
> an exception will be raised immediately.

Something like the attached?  (It does not expose other channel
methods or attributes than send/send_exception/receive, but that
should be an easy).

-- 
Sune Kirkeby | "Never be afraid to tell the world who you are."
             |                                         -- Anonymous
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import stackless, weakref

class ChannelWrapper:
    __slots__ = ['real', 'sender', 'receiver']
    def __init__(self, channel):
        self.real = channel

class SendingChannel:
    __slots__ = ['channel']
    def __init__(self, channel):
        self.channel = channel
        self.channel.sender = weakref.ref(self)
    def send(self, *args):
        assert not self.channel.receiver() is None
        return apply(self.channel.real.send, args)
    def send_exception(self, *args):
        assert not self.channel.receiver() is None
        return apply(self.channel.real.send_exception, args)

class ReceivingChannel:
    __slots__ = ['channel']
    def __init__(self, channel):
        self.channel = channel
        self.channel.receiver = weakref.ref(self)
    def receive(self):
        assert not self.channel.sender() is None
        return self.channel.real.receive()

def dualchannel():
    channel = ChannelWrapper(stackless.channel())
    return SendingChannel(channel), ReceivingChannel(channel)

if __name__ == '__main__':
    print 'Testing . . .'

    s, r = dualchannel()
    def f(s):
        stackless.tasklet().become()
        s.send(42)
    f(s)
    assert r.receive() == 42
    print 'send / receive seems ok.'
    
    try:
        s, r = dualchannel()
        del s
        r.receive()
    except AssertionError:
        print 'receive seems ok.'
    else:
        print 'receive seems borked.'

    try:
        s, r = dualchannel()
        del r
        s.send(42)
    except AssertionError:
        print 'send seems ok.'
    else:
        print 'send seems borked.'