Detecting recursion loops

[fumanchu]

robert wrote:
> Ben Finney wrote:
> > robert <no-spam at no-spam-no-spam.invalid> writes:
> >
> >> Carl Banks wrote:
> >>> 2. Consider whether you're unwittingly trying to cover up a bug.
> >>> ISTM no matter how problematic the input is, you should at least
> >>> be able to make progress on it.  Are you getting this error
> >>> because, say, you're not incrementing a counter somewhere, and
> >>> thus recalling a function with the same arguments again?
> >> the "bug" comes in from the I/O input.
> >
> > If a program doesn't gracefully deal with bad input, that's a bug in
> > the program. You should be designing your input handler so that it
> > will do something helpful (even if that's to stop immediately with an
> > informative error message) in the event of bad input, rather than
> > allowing that bad data to send your program into an endless loop.
>
>
> Yet that detection is what the asked alg should do.
> Example: When a HTML-(content)-relaying sends
> you around in a circle through a complex handler chain.

You might find some engineering inspiration in CherryPy's
InternalRedirect handler [1], which simply raises an error if you visit
the same state twice. Another option is to periodically check a
timeout, which CherryPy does via an Engine.monitor thread [2] (that
runs Response.check_timeout [3]). Note that either approach requires
some alteration to the code being inspected.


Robert Brewer
System Architect
Amor Ministries
fumanchu at amor.org

[1]
http://www.cherrypy.org/browser/tags/cherrypy-3.0.0RC1/cherrypy/_cpwsgi.py
[2]
http://www.cherrypy.org/browser/tags/cherrypy-3.0.0RC1/cherrypy/_cpengine.py#L240
[3]
http://www.cherrypy.org/browser/tags/cherrypy-3.0.0RC1/cherrypy/_cprequest.py#L565