【10.1】python中的GIL

#!/user/bin/env python
# -*- coding:utf-8 -*-

# gil global interpreter lock（cpython）全局解释器锁
# python中一个线程对应于c语言中的一个线程
# gil时的同一时刻只有一个线程在一个cpu上执行字节码，无法将多个线程映射到多个cpu上执行
# gil会根据执行的字节码行数以及时间片释放gil，gil在遇到io操作时主动释放
import threading
total = 0


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


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


thread1 = threading.Thread(target=add)
thread2 = threading.Thread(target=desc)

thread1.start()
thread2.start()

thread1.join()
thread2.join()

print(total)

C:UsersAdministratorPythonimooc>python demo.py
-102343

C:UsersAdministratorPythonimooc>python demo.py
-29159

C:UsersAdministratorPythonimooc>python demo.py
-239340