import threading
import time
class MyThread(threading.Thread):
    def run(self):
        global num
        time.sleep(1)
    
        if mutex.acquire(1):
            num +=1
            msg = self.name + 'set num to ' +str(num)
            print msg
            mutex.release()
num = 0
mutex = threading.Lock()
def test():
    for i in range(5):
        t = MyThread()
        t.start()
if __name__=="__main__":
    test()