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Python-Threading. Thread vs Threading. Python offers two thread modules Thread : used up to now; including this homework. start_new_thread() : simple mechanism that hides many details of running athread Locking : Threading : Thread class which we subclass and override run().
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Python-Threading Programming Robots
Programming Robots Thread vs Threading • Python offers two thread modules • Thread: used up to now; including this homework. • start_new_thread(): simple mechanism that hides many details of running athread • Locking: • Threading: • Thread class which we subclass and override run(). vlock = thread.allocate_lock() vlock.acquire() ... vlock.release()
Programming Robots Program Paradigm: • Create two robot objects. • Subclass Thread and implement run(). • Create two threads and start them • Wait in the main thread until the two child threads are done. • Avoid infinite loops that consume CPU cycles
Programming Robots Whirling Dervishes
Programming Robots Using Threading: • The key here is to avoid having the thread constantly consuming CPU cycles by checking if it is time to do its thing. • The threading.Event class will cause the thread that calls the threading.Event.wait() method to go to sleep. • It will stay asleep until it is awoken by another thread calling the threading.Event.set() method. • In order for the wait() method to do the correct thing in the future it is important to call threading.Event.clear().
Programming Robots Robot Methods: Wait: This method invokes the Event.wait() method and always returns False. Dflt: This method determines direction to to turn and returns True calling doRotate()
Programming Robots Code def main(): d1 = WhirlingDervish(0,0) d2 = WhirlingDervish(0,0) d1.addToProgramList('Wait') d1.addToProgramList('dflt') d2.addToProgramList('Wait') d2.addToProgramList('dflt') t1 = MyThread(d1) t2 = MyThread(d2) t1.start() t2.start() t1.join() # blocks until t1 done t2.join() # blocks until t2 done main() from myRobot import * from WhirlingDervish import * import threading class MyThread (threading.Thread): def __init__(self,wd): threading.Thread.__init__(self) self.myDerv = wd def run(self): self.myDev.main(120)
Programming Robots More Code: from myro import * from myRobot import * from random import Random import threading class WhirlingDervish (MyScribbler): myEvent = threading.Event() myLock = threading.Lock() direction = 1 def __init__(self,port,t=0,r=0): MyScribbler.__init__(self,port,t,r) # add additional behaviours here for this program only self.masterMethodsList['Wait'] = self.Wait self.masterMethodsList['dflt'] = self.dflt
Programming Robots def Wait(self): # instead of consuming CPU time this dervish goes to sleep print 'Waiting' WhirlingDervish.myEvent.wait() # upon waking up; it fails through to the default method return [False,self.T,self.R,self.move] def dflt(self): rotate = +1 if (WhirlingDervish.direction == -1): rotate = -1 # dflt always succeeds return [True,0,rotate,self.doRotate]
Programming Robots More Code def doRotate(self,t,r): global direction self.move(t,r) sleep(Random.random()*4.0) self.stop() WhirlingDervish.myLock.acquire() if (Random.random() < 0.5) : WhirlingDervish.direction = 1 else: WhirlingDervish.direction = -1 WhirlingDervish.myLock.release() WhirlingDervish.myEvent.set() WhirlingDervish.myEvent.clear()
Programming Robots Other threading Clases • Event.set() wakes up all threads waiting on the same event. • We work at a lower level – threading.Condition. • In threading.Condition we use two methods – notify() and notifyAll(). NotifyAll() is just Event.set(). • Notify() tells the thread manager to awaken one waiting thread, we don't know which.
