[Stackless] Example Re: Requesting Comments for a Deadlock Detection Module
andrewfr_ice at yahoo.com
Wed Apr 8 20:55:18 CEST 2009
--- On Fri, 4/3/09, Richard Tew <richard.m.tew at gmail.com> wrote:
Sorry for being so tardy in responding. And thanks for the helpful feedback.
> The best time to try out something like this, is of course
> when the problem unexpectedly arises. Unless anyone has any
> outstanding deadlocks they are working around, it might be hard to do
Well from reading this mailing list, I have seen a few examples of developers complaining about deadlock. So deadlock does happen. The problem is recognizing it. It would help if I had more examples other my own. I am still trying to figure out the limits of my approach. I want to punch holes in the detector.
> It might be worthwhile do something along these lines:
The semester ends soon so I can do most of this. Also I would need an account.
> Personally, I prefer a postmortem approach like this:
I find this URL very helpful. I haven't played with frames and traceback so I found the example helpful. Yes, it is useful to give stuff like the line number.
This may also get me into looking at debugging.
> Place the deadlock detection at the lowest level and
> periodically monitor unexpected behaviour. Then when unpredictable
> behaviour occurs in a live situation, which is not likely
> reproducible in a test environment, postmortem information is available.
I am not sure what lowest level means....
Well the way the detector currently works is that it runs once the Stackless Scheduler has decided there is deadlock. Perhaps a more obtrusive detector could wrap channels, hook into schedule.call_back, execute and throw an exception. However I doubt if this is much better.
I feel, provided the detector works on all but the most trivial examples, and one is scared of deadlock, the programmer will throw in the few extra lines of code (registerResources).
> And unpredictability in my experience, tends to be best
> demonstrated by as full a picture of the logic flow as possible.
Yes I agree. Let me play with this.
>This means a call stack with local variables.
Well the detector as it stands, ought to tell you about the contentious channels involved in the deadlock. I suspect analysing the local
variables will give you all the channels available to the deadlocked tasklet. This is more than you may need.
Thanks for the suggestions.
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