That makes sense, thank you. A timeout seems unlikely but maybe the client is closing the connection due to a network issue. This is an extremely rare occurrence.
On Sun, Jan 24, 2021 at 2:41 PM Glyph <gl...@twistedmatrix.com> wrote: > While a socket is open and receiving data, recv() will either give you a > non-zero number of bytes if bytes are ready, or an EWOULDBLOCK (AKA EAGAIN) > if no bytes are ready. A result of zero bytes (the empty string) means > "end of file" - the other end has closed the socket. > > So what's happening here is your client is timing out or otherwise > canceling its request by closing the socket, and this is the correct, > intentional response to that scenario. > > -g > > On Jan 24, 2021, at 11:57 AM, Robert DiFalco <robert.difa...@gmail.com> > wrote: > > 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 >> > _______________________________________________ > Twisted-Python mailing list > Twisted-Python@twistedmatrix.com > https://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python > > > _______________________________________________ > Twisted-Python mailing list > Twisted-Python@twistedmatrix.com > https://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python >
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