import threading

balance = 0
def change(n):
    global balance
    balance += n
    balance -= n

lock = threading.Lock()  # 获取线程锁

def run_thread(n):
    for i in range(100000):
        # 方式一：
        # 获取锁
        # lock.acquire()
        # try:
        #     change(n)
        # finally:
        #     # 释放锁
        #     lock.release()
        # 方式二：
        with lock:
            change(n)

t1 = threading.Thread(target=run_thread, args=(4,))
t2 = threading.Thread(target=run_thread, args=(8,))

t1.start()
t2.start()

t1.join()
t2.join()

print(balance)