python多线程threading及锁机制

1，多线程无锁情况下

import threadingimport timebalance = 0def change_it(n):    global balance    balance = balance + n    balance = balance - ndef run_thread(n):    for i in range(10000):               change_it(n)t1 = threading.Thread(target = run_thread, args = (5, ))  //创建一个线程t1t2 = threading.Thread(target = run_thread, args = (8, ))  //创建一个线程t2t1.start()  //开启线程t2.start()t1.join()    //等待线程结束t2.join()print(balance)打印结果理论上是0，实际上不确定，因为线程t1和线程t2存在竞争资源的情况，导致结果的不确定性，可以多运行几次来观察结果2，给资源加锁
import threadingimport timebalance = 0lock = threading.Lock()  //创建锁def change_it(n):    global balance    balance = balance + n    balance = balance - ndef run_thread(n):    for i in range(10000):        lock.acquire()   //使用锁        change_it(n)        lock.release()   //释放锁t1 = threading.Thread(target = run_thread, args = (5, ))t2 = threading.Thread(target = run_thread, args = (8, ))t1.start()t2.start()t1.join()t2.join()print(balance)
由于多线程是不安全的，有必要给资源加锁，打印结果必定是0