You're absolutely right, I meant "cancel the deferred". I don't grok server sockets very well so maybe someone can help. But apparently, klein does a .doRead from our server socket (getting the request from the client?). This returns a "why" of "connection done" so that closes the connection before we have written our response to the client, and that cancels the deferred SQS write.
https://github.com/racker/python-twisted-core/blob/master/twisted/internet/selectreactor.py#L148-L155 The method above is "doRead". Which calls this: https://github.com/twisted/twisted/blob/trunk/src/twisted/internet/tcp.py#L239 I guess if If socket.rcv() returns an empty string it simply closes the connection. https://github.com/twisted/twisted/blob/trunk/src/twisted/internet/tcp.py#L249-L250 Is that normal? I mean I guess it must be but then why is the read getting an empty string and closing the connection? I can't really account for it? Some kind of back pressure due to load? Thanks for any thoughts. On Sun, Jan 24, 2021 at 11:32 AM Colin Dunklau <colin.dunk...@gmail.com> wrote: > > > On Sun, Jan 24, 2021 at 11:45 AM Robert DiFalco <robert.difa...@gmail.com> > wrote: > >> Hi, I apologize this question is a little vague. I'm looking for >> pointers. I have a klein route that makes an underlying deferToThread call >> with a simple single thread (an IO based sync call I can't change, a boto3 >> sqs write). The thread pool is simple, just a couple of threads, nothing >> fancy. >> >> VERY rarely it appears that Klein cancels the thread. What techniques can >> I use to figure out why my thread is being Canceled? There's nothing in the >> failure to tell me "who, why, or where" it was canceled. Also, I cannot get >> this down to a reproducible case, but here's the boto3 sqs wrapper, this >> fall back works fine, but it's a band-aide for an error I can't track down.: >> >> def write(self, payload): >> """ >> Write message to SQS async from thread pool. If twisted cancels the >> thread, instead write synchronously. >> >> def _retrySynchronously(error): >> if error.type != CancelledError: >> return error >> >> log.warn("Async SQS write cancelled. Calling synchronously.") >> return defer.succeed(self._writeSyncFallback(payload)) >> >> deferredCall = self._deferToThread(self.sqs.write, payload) >> deferredCall.addErrback(_retrySynchronously) >> return deferredCall >> >> def _writeSyncFallback(self, payload): >> return self.sqs.write(payload) >> >> The _deferToThread call just uses my own thread pool with 2 threads, but >> is otherwise stock. >> >> Is there a level of logging I'm missing or some other thing that would >> tell me why the thread is being canceled? The retry works great and Klein >> does not return an error from the route. >> >> Thanks in advance. >> >> > I think we'll need to see more code for this, specifically the caller of > that `write` method, and its callers, etc. Note that the thread itself > isn't being cancelled, the Deferred you get from _deferToThread is... so > you'll most likely need to find out what code interacts with that object to > progress in isolating this. > > In my quick skim of the deferToThread and ThreadPool source, I can't find > any explicit cancellations. While that certainly doesn't rule it out, it > does make me think you're more likely to find the issue by inspecting the > callers involved. > _______________________________________________ > Twisted-Python mailing list > Twisted-Python@twistedmatrix.com > https://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python >
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