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    <p>I would approach your needs using threads and locks.</p> <p>In fact, I love an open sourced ThreadPool written by Pepe, a friend of mine.</p> <p>Here is ThreadPool code, and after that, a possible solution:</p> <pre><code>#! /usr/bin/python # -*- coding: utf-8 -*- # File: threadPool.py import threading import Queue import time import sys import traceback import datetime Instance = None def getInstance(): global Instance if not Instance: Instance = ThreadPool() return Instance class ThreadPool: def __init__(self,maxWorkers = 10): self.tasks = Queue.Queue() self.workers = 0 self.working = 0 self.maxWorkers = maxWorkers self.allKilled = threading.Event() self.countLock = threading.RLock() self.timers = {} self.timersLock = threading.Lock() self.timersThreadLock = threading.Lock() self.timersEvent = threading.Event() self.allKilled.set() def run(self,target,callback = None, *args, **kargs): """ starts task. target = callable to run with *args and **kargs arguments. callback = callable executed when target ends callback sould accept one parameter where target's return value is passed. If callback is None it's ignored. """ self.countLock.acquire() if not self.workers: self.addWorker() self.countLock.release() self.tasks.put((target,callback,args,kargs)) def setMaxWorkers(self,num): """ Sets the maximum workers to create. num = max workers If number passed is lower than active workers it will kill workers to match that number. """ self.countLock.acquire() self.maxWorkers = num if self.workers &gt; self.maxWorkers: self.killWorker(self.workers - self.maxWorkers) self.countLock.release() def addWorker(self,num = 1): """ Add workers. num = number of workers to create/add. """ for x in xrange(num): self.countLock.acquire() self.workers += 1 self.allKilled.clear() self.countLock.release() t = threading.Thread(target = self.__workerThread) t.setDaemon(True) t.start() def killWorker(self,num = 1): """ Kill workers. num = number of workers to kill. """ self.countLock.acquire() if num &gt; self.workers: num = self.workers self.countLock.release() for x in xrange(num): self.tasks.put("exit") def killAllWorkers(self,wait = None): """ Kill all active workers. wait = seconds to wait until last worker ends if None it waits forever. """ self.countLock.acquire() self.killWorker(self.workers) self.countLock.release() self.allKilled.wait(wait) def __workerThread(self): while True: task = self.tasks.get() # exit is "special" tasks to kill thread if task == "exit": break self.countLock.acquire() self.working += 1 if (self.working &gt;= self.workers) and (self.workers &lt; self.maxWorkers): # create thread on demand self.addWorker() self.countLock.release() fun,cb,args,kargs = task try: ret = fun(*args,**kargs) if cb: cb(ret) except: ty,val,tb = sys.exc_info() print "Thread Catch:%s" % "".join(traceback.format_exception(ty,val,tb)) self.countLock.acquire() self.working -= 1 self.countLock.release() del(fun) # Dereference all del(cb) del(args) del(kargs) del(task) self.countLock.acquire() self.workers -= 1 if not self.workers: self.allKilled.set() self.countLock.release() def timer(self, cb, period): """ Add or remove timers. cb = callback function. period = period in seconds (float) if period is 0 timer is deleted. """ self.run(self.__timerThread, None, cb, period) def __timerThread(self, cb, period): self.timersLock.acquire() self.timersEvent.set() if not period: if cb in self.timers: del(self.timers[cb]) self.timersLock.release() return self.timers[cb] = [period,time.time()] self.timersLock.release() if not self.timersThreadLock.acquire(0): return while True: self.timersLock.acquire() if len(self.timers) == 0: self.timersThreadLock.release() self.timersLock.release() break minWait = 30*24*3600 now = time.time() for k,v in self.timers.items(): period, last = v wait = period - (now - last) if wait &lt;=0: self.run(k) wait = period v[1] = now if wait &lt; minWait: minWait = wait self.timersLock.release() self.timersEvent.wait(minWait) self.timersEvent.clear() </code></pre> <p>And a possible solution:</p> <pre><code>#! /usr/bin/python # -*- coding: utf-8 -*- # File: a.py import threadPool import time import threading class A: def __init__(self): self.a = 1 self.alock = threading.Lock() self.tp = threadPool.getInstance() def bar(self): self.alock.acquire() self.a = 1 self.alock.release() def foo(self): self.tp.timer(self.bar, 2) while True: self.alock.acquire() self.a = self.a * 12 self.alock.release() print "A : ",self.a time.sleep(0.1) a = A() a.foo() </code></pre> <p>Run:</p> <pre><code>$ python a.py </code></pre>
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