How well do you know python, part 8

Here is a mostly-functioning class that facilitates writing producer / consumer algorithms. It is designed to support a single producing and multiple consuming threads, i.e., scenarios where consuming involves some blocking operations such as communicating over a socket.

"Mostly," in this case, means that there are two bugs in this class that can be fixed in a total of four or five lines. One is arguably more subtle than the other, but they involve the same part of the code. Can you spot them?

Warning: this one is tougher than part 2, which also dealt with threading.

import Queue as queue
import threading

class PCQueue:
    def __init__(self, initialthreads):
        self.q = queue.Queue()
        self.running = True
        self.condition = threading.Condition()
        for i in range(initialthreads):
            self.add_consumer()
    def run_consumer(self):
        while True:
            self.condition.acquire()
            try:
                self.condition.wait()
                if not self.running:
                    return
            finally:
                self.condition.release()
            obj = self.q.get()
            self.consume(obj)
    def put(self, obj):
        self.condition.acquire()
        self.q.put(obj)
        self.condition.notify()
        self.condition.release()
    def consume(self, obj):
        raise 'must implement consume method'
    def add_consumer(self):
        threading.Thread(target=self.run_consumer).start()
    def stop(self):
        self.running = False
        self.condition.acquire()
        self.condition.notifyAll()
        self.condition.release()

Here's a short example using PCQueue.

class PCExample(PCQueue):
    def consume(self, url):
        import urllib
        n = len(urllib.urlopen(url).read())
        print '\t%s contains %d bytes' % (url, n)

q = PCExample(2) # 2 threads
while True:
    print 'url? (empty string to quit)'
    url = raw_input()
    if not url:
        break
    q.put(url)
q.stop()