Python练习(day9)

练习1、模拟抢车票（进程同步 锁）
	代码1：（并发运行,效率高,但竞争同一文件,数据写入错乱）
		from multiprocessing import Process
		import time,json,random
		def search():
				dic=json.load(open('db.txt'))
				print('剩余票数%s' %dic['count'])
		def get():
				dic=json.load(open('db.txt'))
				time.sleep(0.1) #模拟读数据的网络延迟
				if dic['count'] >0:
						dic['count']-=1
						time.sleep(0.2) #模拟写数据的网络延迟
						json.dump(dic,open('db.txt','w'))
						print('购票成功')
		def task():
				search()
				get()
		for i in range(3): #模拟并发100个客户端抢票
				p=Process(target=task)
				p.start()
	代码2：加锁：由并发变成了串行,牺牲了运行效率,但保证了数据的安全
		from multiprocessing import  Process,Lock
		import json,time
		def search():
				dic=json.load(open('db.txt'))
				print('剩余票数%s' %dic['count'])
		def get():
				dic = json.load(open('db.txt'))
				time.sleep(0.1)
				if dic['count']>0:
						dic['count']-=1
						time.sleep(0.1)
						json.dump(dic,open('db.txt','w'))
						print('购票成功')
				else:
						print('没票了')
		def task(lock):
				search()
				lock.acquire()
				get()
				lock.release()
		lock=Lock()
		for i in range(3):
				p=Process(target=task,args=(lock,))
				p.start()