#!/usr/bin/python2.7#File: threadsNum.py#Author: lxw#Time: 2014-09-07#Usage: Demonstration for control the number of threads.import threadingfrom myThread import MyThreadfrom time import sleepdef fib(x):    sleep(0.005)    if x < 2:        return 1    return fib(x-2) + fib(x-1)argList = [13, 11, 15, 12, 14]def main():    #Limit the number of threads to 3.    threadingNum = threading.Semaphore(3)    threads = []    for arg in argList:        t = MyThread(fib, (arg,), threadingNum, fib.__name__+str(arg))        threads.append(t)    #There are 5 threads in all, but at most 3 of them run at the same time.    for thread in threads:        thread.start()    for thread in threads:        #if t is threading.currentThread():        #    continue        thread.join()        print(thread.getResult())if __name__ == ‘__main__‘:    main()else:    print(‘Being imported as a module.‘)

#!/usr/bin/python2.7#File: myThread.py#Author: lxw#Time: 2014-09-06import threadingfrom time import ctimeclass MyThread(threading.Thread):    def __init__(self, func, args, num, name=""):        #if the subclass overrides the constructor, it must make sure to invoke the base class constructor (Thread.__init__()) before doing anything else to the thread.        threading.Thread.__init__(self)        self.func = func        self.args = args        self.threadingNum = num        self.name = name    def getResult(self):        return self.res    def run(self):        #NOTE: "with".        with self.threadingNum:            print("start {0} at: {1}".format(self.name, ctime()))            self.res = apply(self.func, self.args)            print("end {0} at: {1}".format(self.name, ctime()))

lxw@lxw-PC:TASK2$ python threadsNum.py start fib13 at: Sun Sep  7 16:11:23 2014start fib11 at: Sun Sep  7 16:11:23 2014start fib15 at: Sun Sep  7 16:11:23 2014end fib11 at: Sun Sep  7 16:11:24 2014start fib12 at: Sun Sep  7 16:11:24 2014end fib12 at: Sun Sep  7 16:11:26 2014start fib14 at: Sun Sep  7 16:11:26 2014end fib13 at: Sun Sep  7 16:11:26 2014377144end fib14 at: Sun Sep  7 16:11:33 2014end fib15 at: Sun Sep  7 16:11:33 2014987233610