赵凡导师并发知识第一次分享观后感

主要是渗透了解 asyncio  相关概念

提及部分描述：1.线程（阻塞，非阻塞）

　　　　　　　2.线程之间通信（线程之间的传递（import queue））

　　   　　　　 3.进程之间通信（进程之间通信from multiprocessing import Process,Queue  用进程Queue）单独详解）

举例图：

场景描述：

数据库的要操作的表的信息为：

     当多个请求都到数据库操作接口程序的时候，针对同一个name的count进行增加或者减少，就要保证操作的同一个时刻只有一个可以去获取count的值并进行update操作，所以我是在这一步增加了锁，因为使用aiohttp写的，所以想要在这里也用了aiorwlock，但是在我测试的过程中发现了，当一个协程获取锁还没释放锁的时候，另外一个协程也获取到锁，下面我是具体的代码

核心程序：

 

class CntHandler(object):

    def __init__(self, db, loop):
        self.db = db
        self.loop = loop
        self.company_lock = {}

    def response(self, request, msg):
        peer = request.transport.get_extra_info('peername')
        logging.info("request url[%s] from[%s]: %s", request.raw_path, peer, msg)
        origin = request.headers.get("Origin")
        if origin is not None:
            headers = {"Access-Control-Allow-Origin": origin, "Access-Control-Allow-Credentials": "true"}
            resp = web.Response(text=util.dictToJson(msg), content_type='application/json', headers=headers)
        else:
            resp = web.Response(text=util.dictToJson(msg), content_type='application/json')
        return resp

    async def cnt_set(self, request):
        """
        用于设置company表中的count值
        :param request: 
        :return: 
        """
        post = await request.post()
        logging.info('post %s', post)
        company_name = post.get("company")
        cnt = post.get("cnt")
        sql = "update shield.company set count=%s where name=%s"
        args_values = [cnt, company_name]
        rwlock = self.company_lock.get(company_name, "")
        if not rwlock:
            rwlock = aiorwlock.RWLock(loop=self.loop)
            self.company_lock[company_name] = rwlock
        async with rwlock.writer:
            msg = dict()
            po_sql = "select * from shield.company where name=%s"
            po = await self.db.get(po_sql, company_name)
            if not po:  # 找不到企业
                logging.error("not found company name [%s]", company_name)
                msg["code"] = 404
                msg["code"] = "not found company"
                return self.response(request, msg)
            res = await self.db.execute(sql, args_values)
            if not isinstance(res, int):
                logging.error("sql update is err:", res)
                msg["code"] = 403
                msg["reason"] = "set fail"
                return self.response(request, msg)
            logging.info("company [%s] set cnt [%s] is success", company_name, cnt)
            msg["code"] = 200
            msg["reason"] = "ok"
            return self.response(request, msg)

    async def cnt_inc(self, request):
        """
        用于增加company表中的count值
        :param request: 
        :return: 
        """
        post = await request.post()
        logging.info('post %s', post)
        company_name = post.get("company")
        cnt = int(post.get("cnt", 0))
        rwlock = self.company_lock.get(company_name, "")
        if not rwlock:
            rwlock = aiorwlock.RWLock(loop=self.loop)
            self.company_lock[company_name] = rwlock
        async with rwlock.writer:
            uuid_s = uuid.uuid1().hex
            logging.debug("[%s]---[%s]", uuid_s, id(rwlock))
            msg = dict()
            sql = "select * from shield.company where name=%s"
            po = await self.db.get(sql, company_name)
            if not po:  # 找不到企业
                logging.error("not found company name [%s]", company_name)
                msg["code"] = 404
                msg["code"] = "not found company"
                return self.response(request, msg)
            old_cnt = po.get("count")
            po_cnt = int(po.get("count"))
            res = po_cnt + cnt
            update_sql = "update shield.company set count=%s where name=%s"
            args_values = [res, company_name]
            update_res = await self.db.execute(update_sql, args_values)
            if not isinstance(update_res, int):  # 数据库update失败
                logging.error("sql update is err:", update_res)
                msg["code"] = 403
                msg["reason"] = "inc fail"
                return self.response(request, msg)
            logging.info("uuid [%s] lock [%s] company [%s] inc cnt [%s] old cnt [%s]  true will is [%s] success", uuid_s,id(rwlock), company_name, cnt, old_cnt, res)
            msg["code"] = 200
            msg["reason"] = "ok"
            return self.response(request, msg)

    async def cnt_dec(self, request):
        """
        用于减少company表中count的值
        :param request: 
        :return: 
        """
        post = await request.post()
        logging.info('post %s', post)
        company_name = post.get("company")
        cnt = int(post.get("cnt", 0))
        rwlock = self.company_lock.get(company_name, "")
        if not rwlock:
            rwlock = aiorwlock.RWLock(loop=self.loop)
            self.company_lock[company_name] = rwlock
        async with rwlock.writer:
            uuid_s = uuid.uuid1().hex
            logging.debug("[%s]---[%s]", uuid_s, id(rwlock))
            msg = dict()
            sql = "select * from shield.company where name=%s"
            po = await self.db.get(sql, company_name)
            if not po:      # 找不到企业
                logging.error("not found company name [%s]", company_name)
                msg["code"] = 404
                msg["code"] = "not found company"
                return self.response(request, msg)
            po_cnt = int(po.get("count"))
            old_cnt = po.get("count")
            if po_cnt == 0:
                logging.error("company [%s] cnt is 0", company_name)
                msg["code"] = 400
                msg["reason"] = "cnt is 0"
                return self.response(request, msg)
            if po_cnt < cnt:  # 数据库余额不足
                logging.error("company [%s] count is not enough", company_name)
                msg["code"] = 405
                msg["reason"] = "count is not enough"
                return self.response(request, msg)
            res = po_cnt - cnt
            update_sql = "update shield.company set count=%s where name=%s"
            args_values = [res, company_name]
            update_res = await self.db.execute(update_sql, args_values)
            if not isinstance(update_res, int): # 执行update 失败
                logging.error("sql update is err:", update_res)
                msg["code"] = 403
                msg["reason"] = "inc fail"
                return self.response(request, msg)
            logging.info("uuid [%s] lock [%s] company [%s] dec cnt [%s] old cnt [%s] true will is [%s] success",uuid_s,id(rwlock), company_name, cnt, old_cnt, res)

            msg["code"] = 200
            msg["reason"] = "ok"
            return self.response(request, msg)

上面代码出问题的代码是在增加和减少的时候：

async with rwlock.writer:

在一个协程还没有释放锁的时候，另外一个操作也就进来了，到之后在测试并发的时候，对同一个name的count进行操作导致最后的count值不符合的问题

这个完整的代码地址：https://github.com/pythonsite/test_aiorwlock