多进程抢票问题

from multiprocessing import Process, Lock
import json
import time
def read_fares(pop):
    with open("file", "r") as f:
        num = json.loads(f.read())["count"]
    print("%d号获取到还剩%d张票" % (pop, num))

def get_fares(pop):
    with open("file", "r") as f:
        num = json.loads(f.read())["count"]
        time.sleep(0.1)     #模拟读数据的网络延迟
    if num > 0:
        num -= 1
        time.sleep(0.2)      #模拟写数据的网络延迟
        with open("file", "w") as f:
            f.write(json.dumps({"count": num}))
        print("%d号买到票了" % pop)

def task(pop,lock):
    read_fares(pop)
    lock.acquire()
    get_fares(pop)
    lock.release()

if __name__ == "__main__":
    lock = Lock()
    for i in range(10):             #开启十个进程共同抢票
        p = Process(target=task, args=(i, lock))
        p.start()

避免多个进程同时修改文件数据，所以加入进程锁。