Serializing operations in Python, with blocking behavior on the caller side

serialize.py

from threading import Thread, Event
from Queue import Queue

class Proc(Thread):
    def __init__(self, in_queue):
        Thread.__init__(self)
        self.in_queue = in_queue
        self.die = Event()

    def stop(self):
        self.die.set()

    def run(self):
        while True:
            if self.die.is_set():
                break
            (msg, e) = self.in_queue.get()
            e.set()

queue = Queue()
proc = Proc(queue)
proc.daemon = True
proc.start()

def send(msg):
   e = Event()
   queue.put((msg, e))
   e.wait()
   print "sent %s" % msg

class SenderA(Thread):
    def run(self):
        send("a")
        send("b")
        send("c")

class SenderB(Thread):
    def run(self):
        send("x")
        send("y")
        send("z")