python 锁

Posted 2022-01-21 wt7018

作用：异步修改数据时，会造成数据安全问题，子进程分别进入文件/数据库，修改数据

"""
过程：
1.导入Lock模块
2.创建Lock对象
3.Lock对象做为要锁的进程的参数
4.lock.acquire()
5.lock.release()
"""
from multiprocessing import Process
from multiprocessing import Lock


def for_fun(lock):
    lock.acquire()
    pass
    lock.release()


if __name__ == ‘__main__‘:
    lock = Lock()
    p = Process(target=for_fun(), args=(lock, ))

 

# 查看、购买电影票
# 购买要设置锁，涉及到数据的修改
import time
import json
from multiprocessing import Process
from multiprocessing import Lock


def read(name):
    with open(file=‘ticket‘, mode=‘r‘, encoding=‘utf-8‘) as f:
        ret = json.load(f)[‘ticket‘]
        print(‘%s查询，还剩%s张票‘ % (name, ret))


def buy(name, lock):
    lock.acquire()      # 拿钥匙
    with open(file=‘ticket‘, mode=‘r‘, encoding=‘utf-8‘) as f:
        ret = json.load(f)
        time.sleep(0.1)
    if ret[‘ticket‘] > 0:
        ret[‘ticket‘] -= 1

        print(‘%s购买成功‘ % name)
    else:
        print(‘%s购买失败‘ % name)
    time.sleep(0.1)
    with open(file=‘ticket‘, mode=‘w‘, encoding=‘utf-8‘) as f:
        json.dump(ret, f)
        time.sleep(0.1)
    lock.release()      # 还钥匙


if __name__ == ‘__main__‘:
    lock = Lock()
    lock.acquire
    for i in range(1, 3):
        p = Process(target=read, args=(‘tom%s‘ % i, ))
        p.start()
        p = Process(target=buy, args=(‘tom%s‘ % i, lock))
        p.start()
"""
结果：
tom1查询，还剩1张票
tom2查询，还剩1张票
tom2购买成功
tom1购买失败
"""