On 30/09/10 11:48, Chris Withers wrote: > On 30/09/2010 04:45, exar...@twistedmatrix.com wrote: >> On 12:52 am, ch...@simplistix.co.uk wrote: >>> >>> Because I haven't found any permutation that doesn't result in the >>> LoopingCall's calls to `loop` from stopping after the exception. >>> >>> I would be more than ecstatic to be proved wrong ;-) >> >> You keep saying the LoopingCall stops. It does not stop. It is waiting >> for a result. > > What result is it waiting for and how do I pass that from the `loop` > function in my first example when the exception is caught?
It is waiting for the deferred you return to callback/errback. This, I found, was initially non-obvious. I assumed that LoopingCall would be called every N seconds regardless, but it won't. If you return a deferred, the LoopingCall will stop until the deferred callback/errback's, then it will be restarted. This is very useful in some circumstances. > >> If you provide it with a result, it will proceed. > > See above: how do I do that? > >> Glyph >> suggested a number of (hackfully) mechanisms you might use to provide it >> with a result. > > Why do you say hackfully? I'm trying to build a scheduler that is Because this is (apparently) a bug in the underlying Twisted code, so anything you do to fix that is a hack. The quickest way I can describe it is this; as I understand, any Twisted function which returns a deferred should never raise an Exception. The exception should instead flow down the errback. This is because (as you've discovered) there are circumstances when a function is called in Twisted where the exception can't propagate "up" to the caller, because the caller is no longer higher in the call stack. Most prominent is reactor.callLater. > resilient to failure in a scheduled task. Yes, of course I want to fix > that failure, but I don't want a failure in one scheduled task to > prevent any further scheduled tasks from being executed... > >> I suggested another way (fix the broken code, or at >> least supply enough information for someone else to fix it). > > For all I know, it's already fixed in a newer version of Twisted > (unfortunately, I can't move this project to a newer version of Twisted) > but once I have a robust scheduler, I'll certainly do my best to report > the underlying failure to you guys properly... If you can produce a short example that uses the real Twisted API which fails, people might a) be able to find/fix the bug and b) suggest a less hacky way of ensuring you see the error. _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
