有一个tornado的脚本，当客户端请求时服务器会向某处发出一个长耗时的http请求，但是当客户端停止请求时服务端的那一个请求也就毫无意义。
如何知晓客户端的连接情况？
重写self.on_finish()
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客户端单方面终止连接要么就是给服务器发送finish消息，要不就得等服务器超时。要不然你单方面断了，服务器不可能一直傻等着浪费资源吧。。
RequestHandler.on_connection_close()
Called in async handlers if the client closed the connection.
Override this to clean up resources associated with long-lived connections. Note that this method is called only if the connection was closed during asynchronous processing; if you need to do cleanup after every request override on_finish instead.
Proxies may keep a connection open for a time (perhaps indefinitely) after the client has gone away, so this method may not be called promptly after the end user closes their connection.http://www.tornadoweb.org/en/stable/web....