锁 与抢票软件的应用

模拟一个简单的抢票软件

import time
import json
from multiprocessing import Process,Lock
def search(person):
    with open('ticket') as f:
        dic = json.load(f)
    time.sleep(0.2)
    print('%s查票余额：'%person,dic['count'])
def get_ticket(person):
    with open('ticket') as f:
        dic = json.load(f)
    time.sleep(0.2)
    if dic['count'] >0:
        print('%s买到票了'%person)
        dic['count'] -=1
        time.sleep(0.2)
        with open('ticket','w') as f:
            json.dump(dic,f)
    else:
        print('%s没买到票'%person)
def ticket(person,lock):
    search(person)
    lock.acquire()            # 加锁
    get_ticket(person)
    lock.release()　　　　　　　 #解锁
if __name__ == '__main__':
    lock = Lock()
    for i in range(1,10):
        p = Process(target=ticket,args=('person%s'%i,lock))
        p.start()

1、为了保证数据的安全
2、在异步的情况下，多个进程有可能同时修改同一份资源
3、就给这个修改的过程加锁


本质：降低了程序的效率，让原本能够执行的代码变成顺序执行，异步变同步的过程。

import time
from multiprocessing import Process,Lock
def func(num,lock):
    time.sleep(1)
    print('***异步执行',num)
    lock.acquire()
    time.sleep(0.5)
    print('同步执行',num)
    lock.release()
if __name__ == '__main__':
    lock = Lock()
    for i in range(10):
        p = Process(target=func,args=(i,lock))
        p.start()