[Python-Dev] stack check on Unix: any suggestions? (original) (raw)

M.-A. Lemburg mal@lemburg.com
Wed, 30 Aug 2000 11:56:31 +0200

"Martin v. Loewis" wrote:

> Does anyone have suggestions for how to detect unbounded recursion > in the Python core on Unix platforms? I just submitted patch 101352, at http://sourceforge.net/patch/?func=detailpatch&patchid=101352&groupid=5470 This patch works on the realistic assumption that reliable stack usage is not available through getrusage on most systems, so it uses an estimate instead. The upper stack boundary is determined on thread creation; the lower stack boundary inside the check. This must allow for initial stack frames (main, entry, etc), and for pages allocated by on the stack by the system. At least on Linux, argv and env pages count towards the stack limit. If some systems are known to return good results from getrusage, that should be used instead. I have tested this patch on a Linux box to detect recursion in both the example of bug 112943, as well as the foo() recursion; the latter would crash with stock CVS python only when I reduced the stack limit from 8MB to 1MB. Since the patch uses a heuristic to determine stack exhaustion, it is probably possible to find cases where it does not work. I.e. it might diagnose exhaustion, where it could run somewhat longer (rather, deeper), or it fails to diagnose exhaustion when it is really out of stack. It is also likely that there are better heuristics. Overall, I believe this patch is an improvement. While this patch claims to support all of Unix, it only works where getrlimit(RLIMITSTACK) works. Unix(tm) does guarantee this API; it should work on *BSD and many other Unices as well. Comments?

See my comments in the patch manager... the patch looks fine except for two things: getrlimit() should be tested for usability in the configure script and the call frequency of PyOS_CheckStack() should be lowered to only use it for potentially recursive programs.

Apart from that, this looks like the best alternative so far :-)

-- Marc-Andre Lemburg

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