threading多线程资源加锁

threading多线程资源加锁控制

# 线程.
import threading


def incr(n):
    global a
    for i in range(n):
        try:
            lock.acquire()  # 加锁相当于单线程了, 所以加锁的位置应该少;(py自带GIL锁).
            a += 1
        finally:
            lock.release()


def decr(n):
    global a
    for i in range(n):
        try:
            lock.acquire()
            a -= 1
        finally:
            lock.release()


if __name__ == "__main__":
    lock = threading.Lock()  # create Lock obj.
    a = 0
    n = 1000000  # 不加Lock, 如果这里n的值过大, 那么计算出的来的a的值就不是0了.

    t1 = threading.Thread(target=incr, args=(n,))
    t2 = threading.Thread(target=decr, args=(n,))
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print(a)  # 多线程使用共享资源可能出现异常.使用加锁来解决, Lock

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