[Python-ideas] channel (synchronous queue)

[Matt Joiner]

I'm not sure that your example allows for multiple senders and receivers to
block at the same time. I'm also not sure why the senders are receiving
values. It's definitely an interesting approach to use a Barrier but
incomplete.
On Feb 19, 2012 2:57 AM, "Arnaud Delobelle" <arnodel at gmail.com> wrote:

> On 18 February 2012 15:38, Matt Joiner <anacrolix at gmail.com> wrote:
> > Recently (for some) the CSP style of channel has become quite popular
> > in concurrency implementations. This kind of channel allows sends that
> > do not complete until a receiver has actually taken the item. The
> > existing  queue.Queue would act like this if it didn't treat a queue
> > size of 0 as infinite capacity.
>
> I don't know if that's exactly what you have in mind, but you can
> implement a channel very simply with a threading.Barrier object (new
> in Python 3.2).  I'm no specialist of concurrency at all, but it seems
> that this is what you are describing (what in the go language is
> called a "synchronous channel" I think):
>
> from threading import Barrier
>
> class Channel:
>    def __init__(self):
>        self._sync = Barrier(2)
>        self._values = [None, None]
>    def send(self, value=None):
>        i = self._sync.wait()
>        self._values[i] = value
>        self._sync.wait()
>        return self._values[1 - i]
>    def get(self):
>        return self.send()
>
> Then with the following convenience function to start a function in a
> new thread:
>
> from threading import Thread
>
> def go(f, *args, **kwargs):
>    thread = Thread(target=f, args=args, kwargs=kwargs)
>    thread.start()
>    return thread
>
> You can have e.g. the scenario:
>
> ch = Channel()
>
> def produce(ch):
>    for i in count():
>        print("sending", i)
>        ch.send(i)
>
> def consume(ch, n):
>    for i in range(n):
>        print("getting", ch.get())
>
> Giving you this:
>
> >>> go(produce, ch)
> sending 0
> <Thread(Thread-103, started 4759019520)>
> >>> go(consume, ch, 3)
> <Thread(Thread-104, started 4763226112)>
> getting 0
> sending 1
> getting 1
> sending 2
> getting 2
> sending 3
> >>> go(consume, ch, 5)
> <Thread(Thread-105, started 4763226112)>
> getting 3
> sending 4
> getting 4
> sending 5
> getting 5
> sending 6
> getting 6
> sending 7
> getting 7
> sending 8
> >>>
>
> --
> Arnaud
>
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