The XMPP example in Twisted.Words crashes if I stop it with Ctrl-C

[jozilla]

The XMPP example (xmpp_client.py) in Twisted words throws an exception when I quit it with Ctrl-C:

Disconnected.
Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/twisted/internet/posixbase.py", line 228, in mainLoop
    self.runUntilCurrent()
  File "/usr/lib/python2.5/site-packages/twisted/internet/base.py", line 561, in runUntilCurrent
    call.func(*call.args, **call.kw)
  File "/usr/lib/python2.5/site-packages/twisted/internet/base.py", line 414, in _continueSystemEvent
    callable(*args, **kw)
  File "/usr/lib/python2.5/site-packages/twisted/internet/base.py", line 375, in disconnectAll
    failure.Failure(main.CONNECTION_LOST))
--- <exception caught here> ---
  File "/usr/lib/python2.5/site-packages/twisted/python/log.py", line 48, in callWithLogger
    return callWithContext({"system": lp}, func, *args, **kw)
  File "/usr/lib/python2.5/site-packages/twisted/python/log.py", line 33, in callWithContext
    return context.call({ILogContext: newCtx}, func, *args, **kw)
  File "/usr/lib/python2.5/site-packages/twisted/python/context.py", line 59, in callWithContext
    return self.currentContext().callWithContext(ctx, func, *args, **kw)
  File "/usr/lib/python2.5/site-packages/twisted/python/context.py", line 37, in callWithContext
    return func(*args,**kw)
  File "/usr/lib/python2.5/site-packages/twisted/internet/tcp.py", line 576, in connectionLost
    Connection.connectionLost(self, reason)
  File "/usr/lib/python2.5/site-packages/twisted/internet/tcp.py", line 416, in connectionLost
    protocol.connectionLost(reason)
  File "/usr/lib/python2.5/site-packages/twisted/words/xish/xmlstream.py", line 82, in connectionLost
    self.dispatch(self, STREAM_END_EVENT)
  File "/usr/lib/python2.5/site-packages/twisted/words/xish/utility.py", line 227, in dispatch
    self._eventObservers[(priority, event)].callback(object)
  File "/usr/lib/python2.5/site-packages/twisted/words/xish/utility.py", line 37, in callback
    methodwrapper(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/twisted/words/xish/utility.py", line 21, in __call__
    self.method(*nargs, **nkwargs)
  File "xmpp_client.py", line 58, in disconnected
    reactor.stop()
  File "/usr/lib/python2.5/site-packages/twisted/internet/base.py", line 342, in stop
    raise RuntimeError, "can't stop reactor that isn't running"
exceptions.RuntimeError: can't stop reactor that isn't running

I already posted this on the mailing list. Here is the comment by Ralph Meijer:

================= I haven't seen that behavior before, but I can confirm this happens. I poked around a bit with the example. It seems that the socket is closed before its factory is shut down. It might be that the reactor shutdown procedure has changed, so I think this behavior is the result of a bug, either in the example or somewhere else. =================

[exarkun]

reformatting description

[exarkun]

(In [23876]) Branching to 'xmpp_client.py-3270'

[exarkun]

I'm not going to finish this now. radix convinced me that we should not introduce a new public API which is only capable of being used as twisted.internet.task.react in this branch is capable of being used. Instead, #1490 should do something about this use-case and the examples should be updated to use that solution.

[ralphm]

exarkun: could you expand a bit on why the current behaves as it does? I don't remember seeing such exceptions when the example code was written. I assume the idiom used in the example is not correct? Also, do you have some kind of work around that could be used until what you suggest should happen on #1490 has been completed?

[exarkun]

It calls reactor.stop() in its connection-lost handler. Also, ^{C calls reactor.stop() and disconnects everything. It needs to keep track of whether the reactor is already in the process of shutting down or not so that it can skip the call if it is. This is basically what I implemented in a general way in the branch.}

[exarkun]

And I love trac markup.

[exarkun]

(In [34897]) Branching to 'xmpp_client.py-3270-2'

[exarkun]

(In [35697]) Branching to 'xmpp_client.py-3270-3'

[exarkun]

Years later, #1490 is still open, so guess we'll go with this.

​Build results

[therve]

OK, I buy that.

• One (blocking) pyflakes: doc/words/examples/xmpp_client.py:23: undefined name 'client_jid'

• It most likely deserves some documentation. Please open a bug if you're not tackling it there.

Thanks, please merge!

[exarkun]

(In [35702]) Slightly improve the react docstring

refs #3270

[exarkun]

(In [35703]) Merge xmpp_client.py-3270-2

Author: exarkun Reviewer: therve Fixes: #3270

Add twisted.internet.task.react, a helper for running and stopping the reactor.

[glyph]

Would it be nice to also have a decorator-syntax version of this?

[exarkun]

I don't know, would it? I feel like no. The decorator form (I am guessing, since "decorator-syntax version" is a long way away from a complete specification - if I guessed wrong it's your fault :) would take a perfectly reasonable Deferred-returning function and make it so you can only call it once, and only if the reactor is not running yet.

[glyph]

Replying to exarkun:

I don't know, would it? I feel like no. The decorator form (I am guessing, since "decorator-syntax version" is a long way away from a complete specification - if I guessed wrong it's your fault :) would take a perfectly reasonable Deferred-returning function and make it so you can only call it once, and only if the reactor is not running yet.

Yeah, that would be the naive implementation. I did implement this once: ​amphacks.util.mainpoint. It checks the function's __module__ and only runs it if it's in __main__, in that implementation.