Hi Andrew,
here comes a little input from me about deadlock detection. On 2/27/09 8:28 PM, Andrew Francis wrote:
I envision the deadlock detector used as follows: a developer believes they have deadlock. They include the detection module and use the register() method to tell the detector which channels a tasklet uses. The programme is executed.
Yes. This is what I would do pretty differently. Not using a register method to be called by hand. Instead, I would overwrite the definition of channels and modify the channel methods to do the deadlock detection.
When stackless.run() prematurely returns, the detector goes through the graph, looking for cycles, returning a list of tuples, describing the tasklets and channels in question.
I believe this would be more helpful if done during a channel action, because you then know exactly, which action caused the deadlock, in the end. ...
To help detect hold-and-wait and circular wait, I create a wait-for graph. Wait-for graphs are described in section 16.6 of Silberschatz's "Database System Concepts."
Got no time to look this up, but I believe you know what you are saying. ...
Once the graph is completed, I use a variation of the graph traversal algorithm in Sedgewick. If a cycle is found, the detector stops and the path is returned. I imagine something like pygraph(?) could be used to visual the deadlocked tasklets and channels.
Would it be possible to do that traversal incrementally, updating on every channel action?
Anyhow I have included the code and a simple example. I suspect the detector is naive to catch every case (i know it won't case the of a single tasklet waiting on a single channel). Still I think the detection module would be useful to a new Stackless programmer. Maybe I could use stuff like class decorators to make the module easier to use. Anyhow comments could be appreciated. Enjoy!
Well, isn't that simple approach sufficient: tracking all actions until the deadlock occours, and that's about it? Maybe I was too quick with something :-) Just my 2 cent - chris -- Christian Tismer :^) <mailto:[email protected]> tismerysoft GmbH : Have a break! Take a ride on Python's Johannes-Niemeyer-Weg 9A : *Starship* http://starship.python.net/ 14109 Berlin : PGP key -> http://wwwkeys.pgp.net/ work +49 30 802 86 56 mobile +49 173 24 18 776 fax +49 30 80 90 57 05 PGP 0x57F3BF04 9064 F4E1 D754 C2FF 1619 305B C09C 5A3B 57F3 BF04 whom do you want to sponsor today? http://www.stackless.com/ _______________________________________________ Stackless mailing list [email protected] http://www.stackless.com/mailman/listinfo/stackless
