generators shared among threads

[Alex Martelli]

Paul Rubin <http://phr.cx@NOSPAM.invalid> wrote:

> jess.austin at gmail.com writes:
> > The main problem with this is that the yield leaves the lock locked.
> > If any other thread wants to read the generator it will block. 
> 
> Ouch, good catch.  Do you see a good fix other than try/finally?
> Is there a classical way to do it with coroutines and semaphores?

Jesse's solution from the other half of this thread, generalized:

import Queue

class ReentrantIterator(Queue.Queue):
    def _init(self, iterator):
        self.iterator = iterator
    def _empty(self):
        return False
    def _get(self):
        return self.iterator.next()
    def _put(*ignore):
        raise TypeError, "Can't put to a ReentrantIterator"
    def next(self):
        return self.get()
    def __iter__(self):
        return self

Now, x=ReentrantIterator(itertools.count()) should have all the
properties we want, I think.  The locking is thanks of Queue.Queue and
its sweet implementation of the Template Method design pattern.


Alex