lock锁住没用

老师为什么我按照这个程序例子敲了一边，lock锁住没用，还是错误的money

lock=threading.Lock()
#存钱1000
def deposit(balance):
    for i in range(100):
        time.sleep(0.01)
        lock.acquire()
        balance.value += 1000
        print(balance.value)
        lock.release()




#取钱1000
def withdraw(balance):
    for i in range(100):
        time.sleep(0.01)
        lock.acquire()
        balance.value -= 1000
        print(balance.value)
        lock.release()

if __name__=="__main__":
    balance=Value('i',2000)
    print("初始余额",balance.value)

    t1 = Process(target=deposit, name="thread1", args=(balance,))
    t2 = Process(target=withdraw, name="thread2", args=(balance,))

    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print("最终余额:",balance.value)