使用tornado报错 RuntimeError: Cannot run the event loop while another loop is running

比眉伴天荒 2023-03-12 07:19 15阅读 0赞

** 1.这里只是写了个简单的demo1，来记录为什么报错，见下面代码**

# demo1.py
    
    import tornado.web
    import tornado.ioloop
    import tornado.httpserver
    import tornado.options
    import tornado.httpclient
    
    
    from tornado.options import define, options
    define("port", default=8989, help="run on the given port", type=int)
    
    
    class IndexHandler(tornado.web.RequestHandler):
        def get(self):
            client = tornado.httpclient.HTTPClient()
            response = client.fetch("https://www.baidu.com")
            print(response.body)
            self.write("ok")
    
    
    if __name__ == '__main__':
    
        tornado.options.parse_command_line()
        app = tornado.web.Application(
            handlers=[
                (r"/", IndexHandler)
            ],
            debug=True,
    
        )
        http_server = tornado.httpserver.HTTPServer(app)
        http_server.listen(options.port)
        tornado.ioloop.IOLoop.instance().start()

正是在tornado的服务里面（存在ioloop循环）使用了HTTPClient，所以才报错了，这是因为在tornado 5.0以后只能在tornado服务中使用异步客户端AsyncHTTPClient，

解决使用同步客户端的问题是可以使用python的requests包

**2.如果像下面这样，直接使用是没有问题的（不使用ioloop循环）**

def h():
        http_client = tornado.httpclient.HTTPClient()
        try:
            response = http_client.fetch("https://www.baidu.com")
            print(response.body)
        except tornado.httpclient.HTTPError as e:
            # HTTPError is raised for non-200 responses; the response
            # can be found in e.response.
            print("Error: " + str(e))
        except Exception as e:
            # Other errors are possible, such as IOError.
            print("Error: " + str(e))
        http_client.close()
    
    h()

**3.如果想在tornado（版本5.0以后）服务中使用客户端，那么只能使用AsyncHTTPClient，如下**

import tornado.web
    import tornado.ioloop
    import tornado.httpserver
    import tornado.options
    import tornado.httpclient
    
    
    from tornado.options import define, options
    define("port", default=8989, help="run on the given port", type=int)
    
    
    class IndexHandler(tornado.web.RequestHandler):
        async def get(self):
            client = tornado.httpclient.AsyncHTTPClient()
            response = await client.fetch("https://www.baidu.com")
            print(response.body)
            self.write("ok")
    
    
    if __name__ == '__main__':
    
        tornado.options.parse_command_line()
        app = tornado.web.Application(
            handlers=[
                (r"/", IndexHandler)
            ],
            debug=True,
    
        )
        http_server = tornado.httpserver.HTTPServer(app)
        http_server.listen(options.port)
        tornado.ioloop.IOLoop.instance().start()