GIL锁

global  interpreter lock 金局解释锁, 使得同一时刻只有一个线程在cpu上执行python的字节码文件,无法将多个线程映射到各个cpu上执行.

gil会根据执行的字节码行数或cpu时间片,或io操作,会主动释放gil锁

import threading
total = 0
def add():
    global total
    for i in range(1000000):
        total += 1


def sub():
    global total
    for i in range(1000000):
        total -= 1

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.