Ejemplo con Multiprocessing

import os
import sys

from multiprocessing import Process
from multiprocessing import Queue

class Doer(Process):

    def __init__(self, queue, state=None):
        Process.__init__(self)
        self.queue = queue
        self.state = state

    def _do_on_start(self):
        print "doint stuff on start"
        print "state:", self.state
        print "pid:", os.getpid()
        print

    def _on_end(self):
        print "doint stuff on end"
        print "state:", self.state
        print "pid:", os.getpid()
        print

    def run(self):
        self._do_on_start()

        msg = None
        while msg is None or msg != "exit":
            # blocks here
            msg = self.queue.get()
            print "handling message", msg

            # do stuff here according to the message
            if msg == "ping":
                print "pong"
            elif isinstance(msg, tuple) and len(msg) == 2:
                action, value = msg
                if action == "set-state":
                    self.state = value
                    print "new state:", self.state
            elif msg != "exit":
                print "unknown message", msg

            print

        self._on_end()

def demo():
    queue = Queue()
    print "creating doer from process", os.getpid()
    doer = Doer(queue, 42)
    doer.start()
    queue.put("ping")
    queue.put("foo")
    queue.put(("set-state", "hola!"))

    queue.put("exit")

    doer.join()

if __name__ == "__main__":
    demo()

corriendolo tenemos el resultado

$ python controlled.py
creating doer from process 11784
doint stuff on start
state: 42
pid: 11785

handling message ping
pong

handling message foo
unknown message foo

handling message ('set-state', 'hola!')
new state: hola!

handling message exit

doint stuff on end
state: hola!
pid: 11785

Ejemplo con Threading

Para hacerlo andar con threading hay que solo cambiar de donde importamos las cosas, aquí esta la diferencia:

Notar que el pid de quién lanza doer es igual al que imprime doer.

diff controlled.py controlledthread.py
4,5c4,5
< from multiprocessing import Process
< from multiprocessing import Queue
---
> from threading import Thread as Process
> from Queue import Queue

import os
import sys

from threading import Thread as Process
from Queue import Queue

class Doer(Process):

    def __init__(self, queue, state=None):
        Process.__init__(self)
        self.queue = queue
        self.state = state

    def _do_on_start(self):
        print "doint stuff on start"
        print "state:", self.state
        print "pid:", os.getpid()
        print

    def _on_end(self):
        print "doint stuff on end"
        print "state:", self.state
        print "pid:", os.getpid()
        print

    def run(self):
        self._do_on_start()

        msg = None
        while msg is None or msg != "exit":
            # blocks here
            msg = self.queue.get()
            print "handling message", msg

            # do stuff here according to the message
            if msg == "ping":
                print "pong"
            elif isinstance(msg, tuple) and len(msg) == 2:
                action, value = msg
                if action == "set-state":
                    self.state = value
                    print "new state:", self.state
            elif msg != "exit":
                print "unknown message", msg

            print

        self._on_end()

def demo():
    queue = Queue()
    print "creating doer from process", os.getpid()
    doer = Doer(queue, 42)
    doer.start()
    queue.put("ping")
    queue.put("foo")
    queue.put(("set-state", "hola!"))

    queue.put("exit")

    doer.join()

if __name__ == "__main__":
    demo()

$ python controlledthread.py
creating doer from process 11812
doint stuff on start
state: 42
pid: 11812

handling message ping
pong

handling message foo
unknown message foo

handling message ('set-state', 'hola!')
new state: hola!

handling message exit

doint stuff on end
state: hola!
pid: 11812