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bpo-45753: Make recursion checks more efficient. (GH-29524)

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* Uses recursion remaining, instead of recursion depth to speed up check against recursion limit.
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Mark Shannon 2021-11-16 11:01:57 +00:00 • committed by GitHub
parent 9bf2cbc4c4
commit b931077375
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10 changed files with 50 additions and 43 deletions
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16
Python/sysmodule.c
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@ -1187,20 +1187,14 @@ sys_setrecursionlimit_impl(PyObject *module, int new_limit)
return NULL;
}
/* Issue #25274: When the recursion depth hits the recursion limit in
_Py_CheckRecursiveCall(), the overflowed flag of the thread state is
set to 1 and a RecursionError is raised. The overflowed flag is reset
to 0 when the recursion depth goes below the low-water mark: see
Py_LeaveRecursiveCall().
Reject too low new limit if the current recursion depth is higher than
the new low-water mark. Otherwise it may not be possible anymore to
reset the overflowed flag to 0. */
if (tstate->recursion_depth >= new_limit) {
/* Reject too low new limit if the current recursion depth is higher than
the new low-water mark. */
int depth = tstate->recursion_limit - tstate->recursion_remaining;
if (depth >= new_limit) {
_PyErr_Format(tstate, PyExc_RecursionError,
"cannot set the recursion limit to %i at "
"the recursion depth %i: the limit is too low",
new_limit, tstate->recursion_depth);
new_limit, depth);
return NULL;
}