152 lines
4.9 KiB
Markdown
152 lines
4.9 KiB
Markdown
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## 异步化
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在前面的例子中，我们并没有对`RequestHandler`中的`get`或`post`方法进行异步处理，这就意味着，一旦在`get`或`post`方法中出现了耗时间的操作，不仅仅是当前请求被阻塞，按照Tornado框架的工作模式，其他的请求也会被阻塞，所以我们需要对耗时间的操作进行异步化处理。
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在Tornado稍早一些的版本中，可以用装饰器实现请求方法的异步化或协程化来解决这个问题。
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- 给`RequestHandler`的请求处理函数添加`@tornado.web.asynchronous`装饰器，如下所示：
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```Python
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class AsyncReqHandler(RequestHandler):
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@tornado.web.asynchronous
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def get(self):
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http = httpclient.AsyncHTTPClient()
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http.fetch("http://example.com/", self._on_download)
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def _on_download(self, response):
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do_something_with_response(response)
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self.render("template.html")
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```
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- 给`RequestHandler`的请求处理函数添加`@tornado.gen.coroutine`装饰器，如下所示：
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```Python
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class GenAsyncHandler(RequestHandler):
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@tornado.gen.coroutine
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def get(self):
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http_client = AsyncHTTPClient()
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response = yield http_client.fetch("http://example.com")
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do_something_with_response(response)
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self.render("template.html")
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```
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- 使用`@return_future`装饰器，如下所示：
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```Python
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@return_future
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def future_func(arg1, arg2, callback):
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# Do stuff (possibly asynchronous)
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callback(result)
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async def caller():
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await future_func(arg1, arg2)
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```
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在Tornado 5.x版本中，这几个装饰器都被标记为**deprcated**（过时），我们可以通过Python 3.5中引入的`async`和`await`（在Python 3.7中已经成为正式的关键字）来达到同样的效果。当然，要实现异步化还得靠其他的支持异步操作的三方库来支持，如果请求处理函数中用到了不支持异步操作的三方库，就需要靠自己写包装类来支持异步化。
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下面的代码演示了在读写数据库时如何实现请求处理的异步化。我们用到的数据库建表语句如下所示：
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```SQL
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create database hrs default charset utf8;
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use hrs;
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/* 创建部门表 */
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create table tb_dept
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(
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dno int not null comment '部门编号',
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dname varchar(10) not null comment '部门名称',
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dloc varchar(20) not null comment '部门所在地',
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primary key (dno)
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);
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insert into tb_dept values
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(10, '会计部', '北京'),
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(20, '研发部', '成都'),
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(30, '销售部', '重庆'),
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(40, '运维部', '深圳');
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```
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我们通过下面的代码实现了查询和新增部门两个操作。
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```Python
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import json
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import aiomysql
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import tornado
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import tornado.web
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from tornado.ioloop import IOLoop
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from tornado.options import define, parse_command_line, options
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define('port', default=8000, type=int)
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async def connect_mysql():
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return await aiomysql.connect(
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host='120.77.222.217',
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port=3306,
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db='hrs',
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user='root',
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password='123456',
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)
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class HomeHandler(tornado.web.RequestHandler):
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async def get(self, no):
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async with self.settings['mysql'].cursor(aiomysql.DictCursor) as cursor:
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await cursor.execute("select * from tb_dept where dno=%s", (no, ))
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if cursor.rowcount == 0:
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self.finish(json.dumps({
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'code': 20001,
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'mesg': f'没有编号为{no}的部门'
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}))
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return
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row = await cursor.fetchone()
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self.finish(json.dumps(row))
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async def post(self, *args, **kwargs):
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no = self.get_argument('no')
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name = self.get_argument('name')
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loc = self.get_argument('loc')
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conn = self.settings['mysql']
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try:
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async with conn.cursor() as cursor:
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await cursor.execute('insert into tb_dept values (%s, %s, %s)',
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(no, name, loc))
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await conn.commit()
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except aiomysql.MySQLError:
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self.finish(json.dumps({
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'code': 20002,
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'mesg': '添加部门失败请确认部门信息'
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}))
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else:
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self.set_status(201)
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self.finish()
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def make_app(config):
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return tornado.web.Application(
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handlers=[(r'/api/depts/(.*)', HomeHandler), ],
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**config
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)
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def main():
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parse_command_line()
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app = make_app({
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'debug': True,
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'mysql': IOLoop.current().run_sync(connect_mysql)
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})
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app.listen(options.port)
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IOLoop.current().start()
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if __name__ == '__main__':
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main()
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```
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上面的代码中，我们用到了`aiomysql`这个三方库，它基于`pymysql`封装，实现了对MySQL操作的异步化。操作Redis可以使用`aioredis`，访问MongoDB可以使用`motor`，这些都是支持异步操作的三方库。
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