锁

别看pyhton有个GIL,但是在多线程编程时与java一样,为了保证数据的案例,还是需要用到锁Lock锁.

Lock不是重入锁,在同一个线程中不能多次acquire()

RLock才是重入锁

import threading
from threading import Lock

# 申明一把锁
lock = Lock()

total = 0
def add():
    global total, lock
    for i in range(1000000):
        # 获取锁
        lock.acquire()
        total += 1
        # 释放锁
        lock.release()

def sub():
    global total,lock
    for i in range(1000000):
        # 获取锁
        lock.acquire()
        total -= 1
        # 释放锁
        lock.release()

if __name__ == '__main__':
    t1 = threading.Thread(target=add)
    t2 = threading.Thread(target=sub)
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print(total)   # 并不等于0,说明不是等t1执行完了t2再执行.  这下打印肯定是0