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Asked: 2026-05-20T11:14:28+00:00

Background I’ve recently been a part of a project where twisted was used. We

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Background

I’ve recently been a part of a project where twisted was used. We utilized a TimerService to daemonize a process. And yes, I realize that this approach may have been overkill, but we’re trying to stay consistent and use a proven framework. Yesterday, an exception went unhandled within the LoopingCall which caused the TimerService to fail, but the twistd application was still running (see twisted enhancement request). To avoid this, we would like to stop the service at the end of a catch-all exception handler.

Question

How to stop both the TimerService and the Twistd application from within the LoopingCall callable method? My concern is that the linux process keeps running when the TimerService is unable to handle an exception, even though the TimerService isn’t looping anymore.

For example:


def some_callable():
  try:
    # do stuff
  except SomeSpecificError ex:
    # handle & log error
  except SomeOtherSpecificError ex:
    # handle & log error
  except:
    # log sys.exc_info() details
    # stop service.

NOTE: The following does not work within the callable.


from twisted.internet import reactor
reactor.stop()
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1 Answer

  1. Editorial Team

    You can’t stop the reactor before it starts:

    >>> from twisted.internet import reactor
>>> reactor.stop()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/exarkun/Projects/Twisted/branches/simplify-ssl-4905/twisted/internet/base.py", line 570, in stop
    "Can't stop reactor that isn't running.")
twisted.internet.error.ReactorNotRunning: Can't stop reactor that isn't running.
>>>

    However, as long as the reactor is running already, reactor.stop works fine:

    >>> from twisted.internet import reactor
>>> reactor.callLater(3, reactor.stop)
<twisted.internet.base.DelayedCall instance at 0xb762d2ec>
>>> reactor.run()
[... pause ...]
>>>

    TimerService is a wrapper around LoopingCall. And more specifically, when it starts its LoopingCall, it passes now=True to run. That causes the function to be called the first time immediately, rather than after the specified interval elapses once.

    So when TimerService.startService is called, your function is called. And the reactor isn’t running yet. On that first call to your function, you can’t stop the reactor, because it hasn’t been started.

    This program:

    from twisted.application.internet import TimerService

def foo():
    from twisted.internet import reactor
    reactor.stop()

from twisted.application.service import Application

application = Application("timer stop")
TimerService(3, foo).setServiceParent(application)

    produces these results:

    exarkun@boson:/tmp$ twistd -ny timerstop.tac
2011-03-08 11:46:19-0500 [-] Log opened.
2011-03-08 11:46:19-0500 [-] using set_wakeup_fd
2011-03-08 11:46:19-0500 [-] twistd 10.2.0+r30835 (/usr/bin/python 2.6.4) starting up.
2011-03-08 11:46:19-0500 [-] reactor class: twisted.internet.selectreactor.SelectReactor.
2011-03-08 11:46:19-0500 [-] Unhandled Error
        Traceback (most recent call last):
          File "/home/exarkun/Projects/Twisted/branches/simplify-ssl-4905/twisted/application/service.py", line 277, in startService
            service.startService()
          File "/home/exarkun/Projects/Twisted/branches/simplify-ssl-4905/twisted/application/internet.py", line 284, in startService
            self._loop.start(self.step, now=True).addErrback(self._failed)
          File "/home/exarkun/Projects/Twisted/branches/simplify-ssl-4905/twisted/internet/task.py", line 163, in start
            self()
          File "/home/exarkun/Projects/Twisted/branches/simplify-ssl-4905/twisted/internet/task.py", line 194, in __call__
            d = defer.maybeDeferred(self.f, *self.a, **self.kw)
        --- <exception caught here> ---
          File "/home/exarkun/Projects/Twisted/branches/simplify-ssl-4905/twisted/internet/defer.py", line 133, in maybeDeferred
            result = f(*args, **kw)
          File "timerstop.py", line 5, in foo
            reactor.stop()
          File "/home/exarkun/Projects/Twisted/branches/simplify-ssl-4905/twisted/internet/base.py", line 570, in stop
            "Can't stop reactor that isn't running.")
        twisted.internet.error.ReactorNotRunning: Can't stop reactor that isn't running.

    However, this one works fine:

    from twisted.application.internet import TimerService

counter = 0

def foo():
    global counter
    if counter == 1:
        from twisted.internet import reactor
        reactor.stop()
    else:
        counter += 1

from twisted.application.service import Application

application = Application("timer stop")
TimerService(3, foo).setServiceParent(application)

    And slightly less grossly, so does this one:

    from twisted.application.internet import TimerService

def foo():
    from twisted.internet import reactor
    reactor.callWhenRunning(reactor.stop)

from twisted.application.service import Application

application = Application("timer stop")
TimerService(3, foo).setServiceParent(application)
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