From: Tim Peters <tim.peters@gmail.com>
Date: Wed, 20 Jun 2001 06:57:32 +0000 (+0000)
Subject: gen_iternext():  repair subtle refcount problem.
X-Git-Tag: v2.2a3~1503
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=6302ec63fc40dd6ae1ad3003003b6b264422e8e0;p=thirdparty%2FPython%2Fcpython.git

gen_iternext():  repair subtle refcount problem.
NeilS, please check!  This came from staring at your genbug.py, but I'm
not sure it plugs all possible holes.  Without this, I caught a
frameobject refcount going negative, and it was also the cause (in debug
build) of _Py_ForgetReference's attempt to forget an object with already-
NULL _ob_prev and _ob_next pointers -- although I'm still not entirely
sure how!  Part of the difficulty is that frameobjects are stored on a
free list that gets recycled very quickly, so if there's a stray pointer
to one of them it never looks like an insane frameobject (never goes
trough the free() mangling MS debug forces, etc).
---

diff --git a/Python/ceval.c b/Python/ceval.c
index cf917dbcb564..ea5c5378995a 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -152,6 +152,11 @@ gen_iternext(genobject *gen)
         gen->running = 1;
 	result = eval_frame(f);
         gen->running = 0;
+        /* The connection between this frame and its parent is over now, so
+           must NULL out f_back lest it get decref'ed when gen dies (note
+           that eval_frame sets f->f_back without bumping its refcount:  we
+           never had a fully legit reference to it). */
+	f->f_back = NULL;
         return result;
 }