Hi, We have been using Twisted for a long time and are migrating to 8.0.1. We are finding that code that ran fine with 2.5.0 is giving problems with 8.0.1 and it appears to be related to what is happening in reactor.stop(). The code that is failing looks like this: ########## from twisted.internet import reactor d = doSomeThingThatReturnsADeferred() d.addCallback(handleOK) d.addCallback(lambda _: reactor.stop()) reactor.run() ########## The doSomeThingThatReturnsADeferred method is making XMLRPC calls underneath the hood. When we run this, it runs OK, but then blows up at the end with: Traceback (most recent call last): File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/defer.py", line 185, in addCallbacks self._runCallbacks() File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/defer.py", line 323, in _runCallbacks self.result = callback(self.result, *args, **kw) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/base.py", line 387, in _continueFiring callable(*args, **kwargs) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/base.py", line 524, in disconnectAll failure.Failure(main.CONNECTION_LOST)) --- <exception caught here> --- File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/python/log.py", line 51, in callWithLogger return callWithContext({"system": lp}, func, *args, **kw) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/python/log.py", line 36, in callWithContext return context.call({ILogContext: newCtx}, func, *args, **kw) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/python/context.py", line 59, in callWithContext return self.currentContext().callWithContext(ctx, func, *args, **kw) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/python/context.py", line 37, in callWithContext return func(*args,**kw) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/tcp.py", line 577, in connectionLost self.connector.connectionLost(reason) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/base.py", line 937, in connectionLost self.factory.clientConnectionLost(self, reason) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/web/xmlrpc.py", line 325, in clientConnectionLost self.deferred.errback(reason) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/defer.py", line 264, in errback self._startRunCallbacks(fail) File "/Library/Python/2.5/site-packages/Twisted-8.0.1-py2.5-macosx-10.5-i386.egg/twisted/internet/defer.py", line 293, in _startRunCallbacks raise AlreadyCalledError twisted.internet.defer.AlreadyCalledError: I have checked and there is no failure object in my callback chain - this is internal to Twisted. Has the logic in reactor.stop changed recently? Any ideas about what would be causing this? Thanks Brian