“超时"的正确方法龙卷风中的请求 [英] Right way to "timeout" a Request in Tornado

问题描述

我设法编写了一个相当愚蠢的错误，它会使我的一个请求处理程序运行非常慢的数据库查询.

I managed to code a rather silly bug that would make one of my request handlers run a very slow DB query.

有趣的是，我注意到即使在攻城战完成很久之后的 Tornado 仍然在处理请求(有时是 90 年代之后).(评论 --> 我不是 100% 确定 Siege 的工作原理，但我相当确定它关闭了连接..)

Interesting bit is that I noticed that even long-after siege completed Tornado was still churning through requests (sometimes 90s later). (Comment --> I'm not 100% sure of the workings of Siege, but I'm fairly sure it closed the connection..)

我的问题分两部分:- 当客户端关闭连接时 Tornado 会取消请求处理程序吗?- 有没有办法在 Tornado 中超时请求处理程序?

My question in two parts: - Does Tornado cancel request handlers when client closes the connection? - Is there a way to timeout request handlers in Tornado?

我通读了代码，但似乎找不到任何东西.即使我的请求处理程序在上述 bug 中异步运行，待处理请求的数量也会增加到导致应用程序变慢的程度，最好关闭连接.

I read through the code and can't seem to find anything. Even though my request handlers are running asynchronously in the above bug the number of pending requests piled up to a level where it was slowing down the app and it would have been better to close out the connections.

推荐答案

当客户端断开连接时，Tornado 不会自动关闭请求处理程序.但是，您可以覆盖 on_connection_close 以在客户端断开时收到警报，这将允许您取消连接.上下文管理器(或装饰器)可用于设置处理请求的超时；使用 tornado.ioloop.IOLoop.add_timeout 来安排一些方法，该方法使请求在 timeout 之后超时运行，作为上下文的 __enter__ 的一部分manager，然后在上下文管理器的 __exit__ 块中取消该回调.下面是一个演示这两种想法的示例:

Tornado does not automatically close the request handler when the client drops the connection. However, you can override on_connection_close to be alerted when the client drops, which would allow you to cancel the connection on your end. A context manager (or a decorator) could be used to handle setting a timeout for handling the request; use tornado.ioloop.IOLoop.add_timeout to schedule some method that times out the request to run after timeout as part of the __enter__ of the context manager, and then cancel that callback in the __exit__ block of the context manager. Here's an example demonstrating both of those ideas:

import time
import contextlib

from tornado.ioloop import IOLoop
import tornado.web
from tornado import gen

@gen.coroutine
def async_sleep(timeout):
    yield gen.Task(IOLoop.instance().add_timeout, time.time() + timeout)

@contextlib.contextmanager
def auto_timeout(self, timeout=2): # Seconds
    handle = IOLoop.instance().add_timeout(time.time() + timeout, self.timed_out)
    try:
        yield handle
    except Exception as e:
        print("Caught %s" % e)
    finally:
        IOLoop.instance().remove_timeout(handle)
        if not self._timed_out:
            self.finish()
        else:
            raise Exception("Request timed out") # Don't continue on passed this point

class TimeoutableHandler(tornado.web.RequestHandler):
    def initialize(self):
        self._timed_out = False

    def timed_out(self):
        self._timed_out = True
        self.write("Request timed out!\n")
        self.finish()  # Connection to client closes here.
        # You might want to do other clean up here.

class MainHandler(TimeoutableHandler):

    @gen.coroutine
    def get(self):
        with auto_timeout(self): # We'll timeout after 2 seconds spent in this block.
            self.sleeper = async_sleep(5)
            yield self.sleeper
        print("writing")  # get will abort before we reach here if we timed out.
        self.write("hey\n")

    def on_connection_close(self):
        # This isn't the greatest way to cancel a future, since it will not actually
        # stop the work being done asynchronously. You'll need to cancel that some
        # other way. Should be pretty straightforward with a DB connection (close
        # the cursor/connection, maybe?)
        self.sleeper.set_exception(Exception("cancelled"))


application = tornado.web.Application([
    (r"/test", MainHandler),
])
application.listen(8888)
IOLoop.instance().start()

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