线程加锁

加锁的作用：

1、多个线程同时修改同一个全局变量时，确保不被CPU切片阻断

2、加锁会加长执行时间

 

import threading
import time

metalocA = threading.Lock()
# metalocB = threading.Lock

num = 0
def func1():
    for i in range(1000000):
        global num
        metalocA.acquire()
        num +=1
        metalocA.release()

def func2():
    for i in range(1000000):
        global num
        metalocA.acquire()
        num +=1
        metalocA.release()

def main():
    t1 = threading.Thread(target=func1)
    t2 = threading.Thread(target=func2)
    s_time = time.time()
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    e_time = time.time()
    print(e_time-s_time)

if __name__ == '__main__':
    main()
    print(num)

''''
不加锁：
0.1509230136871338
1261326

加锁：
0.4519648551940918
2000000
'''