sys.setrecursionlimit() now raises RecursionError · pythoncapi/cpython@50856d5 · GitHub
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sys.setrecursionlimit() now raises RecursionError
Issue python#25274: sys.setrecursionlimit() now raises a RecursionError if the new recursion limit is too low depending at the current recursion depth. Modify also the "lower-water mark" formula to make it monotonic. This mark is used to decide when the overflowed flag of the thread state is reset.
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6 files changed

Lines changed: 102 additions & 13 deletions

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‎Doc/library/sys.rst‎

Lines changed: 7 additions & 0 deletions

‎Include/ceval.h‎

Lines changed: 9 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -94,10 +94,16 @@ PyAPI_DATA(int) _Py_CheckRecursionLimit;
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# define _Py_MakeRecCheck(x) (++(x) > _Py_CheckRecursionLimit)
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#endif
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/* Compute the "lower-water mark" for a recursion limit. When
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* Py_LeaveRecursiveCall() is called with a recursion depth below this mark,
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* the overflowed flag is reset to 0. */
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#define _Py_RecursionLimitLowerWaterMark(limit) \
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(((limit) > 200) \
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? ((limit) - 50) \
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: (3 * ((limit) >> 2)))
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#define _Py_MakeEndRecCheck(x) \
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(--(x) < ((_Py_CheckRecursionLimit > 100) \
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? (_Py_CheckRecursionLimit - 50) \
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: (3 * (_Py_CheckRecursionLimit >> 2))))
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(--(x) < _Py_RecursionLimitLowerWaterMark(_Py_CheckRecursionLimit))
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#define Py_ALLOW_RECURSION \
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do { unsigned char _old = PyThreadState_GET()->recursion_critical;\

‎Lib/test/test_sys.py‎

Lines changed: 45 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -201,22 +201,60 @@ def test_recursionlimit_recovery(self):
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if hasattr(sys, 'gettrace') and sys.gettrace():
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self.skipTest('fatal error if run with a trace function')
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# NOTE: this test is slightly fragile in that it depends on the current
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# recursion count when executing the test being low enough so as to
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# trigger the recursion recovery detection in the _Py_MakeEndRecCheck
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# macro (see ceval.h).
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oldlimit = sys.getrecursionlimit()
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def f():
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f()
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try:
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for i in (50, 1000):
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# Issue #5392: stack overflow after hitting recursion limit twice
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sys.setrecursionlimit(i)
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for depth in (10, 25, 50, 75, 100, 250, 1000):
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try:
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sys.setrecursionlimit(depth)
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except RecursionError:
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# Issue #25274: The recursion limit is too low at the
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# current recursion depth
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continue
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# Issue #5392: test stack overflow after hitting recursion
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# limit twice
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self.assertRaises(RecursionError, f)
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self.assertRaises(RecursionError, f)
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finally:
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sys.setrecursionlimit(oldlimit)
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@test.support.cpython_only
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def test_setrecursionlimit_recursion_depth(self):
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# Issue #25274: Setting a low recursion limit must be blocked if the
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# current recursion depth is already higher than the "lower-water
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# mark". Otherwise, it may not be possible anymore to
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# reset the overflowed flag to 0.
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from _testcapi import get_recursion_depth
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def set_recursion_limit_at_depth(depth, limit):
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recursion_depth = get_recursion_depth()
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if recursion_depth >= depth:
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with self.assertRaises(RecursionError) as cm:
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sys.setrecursionlimit(limit)
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self.assertRegex(str(cm.exception),
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"cannot set the recursion limit to [0-9]+ "
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"at the recursion depth [0-9]+: "
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"the limit is too low")
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else:
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set_recursion_limit_at_depth(depth, limit)
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oldlimit = sys.getrecursionlimit()
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try:
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sys.setrecursionlimit(1000)
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for limit in (10, 25, 50, 75, 100, 150, 200):
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# formula extracted from _Py_RecursionLimitLowerWaterMark()
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if limit > 200:
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depth = limit - 50
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else:
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depth = limit * 3 // 4
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set_recursion_limit_at_depth(depth, limit)
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finally:
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sys.setrecursionlimit(oldlimit)
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def test_recursionlimit_fatalerror(self):
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# A fatal error occurs if a second recursion limit is hit when recovering
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# from a first one.

‎Misc/NEWS‎

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Original file line numberDiff line numberDiff line change
@@ -11,6 +11,11 @@ Release date: TBA
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Core and Builtins
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-----------------
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- Issue #25274: sys.setrecursionlimit() now raises a RecursionError if the new
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recursion limit is too low depending at the current recursion depth. Modify
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also the "lower-water mark" formula to make it monotonic. This mark is used
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to decide when the overflowed flag of the thread state is reset.
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- Issue #24402: Fix input() to prompt to the redirected stdout when
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sys.stdout.fileno() fails.
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‎Modules/_testcapimodule.c‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3518,6 +3518,15 @@ test_PyTime_AsMicroseconds(PyObject *self, PyObject *args)
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return _PyTime_AsNanosecondsObject(ms);
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}
35203520

3521+
static PyObject*
3522+
get_recursion_depth(PyObject *self, PyObject *args)
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{
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PyThreadState *tstate = PyThreadState_GET();
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/* substract one to ignore the frame of the get_recursion_depth() call */
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return PyLong_FromLong(tstate->recursion_depth - 1);
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}
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35213530

35223531
static PyMethodDef TestMethods[] = {
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{"raise_exception", raise_exception, METH_VARARGS},
@@ -3694,6 +3703,7 @@ static PyMethodDef TestMethods[] = {
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#endif
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{"PyTime_AsMilliseconds", test_PyTime_AsMilliseconds, METH_VARARGS},
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{"PyTime_AsMicroseconds", test_PyTime_AsMicroseconds, METH_VARARGS},
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{"get_recursion_depth", get_recursion_depth, METH_NOARGS},
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{NULL, NULL} /* sentinel */
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};
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‎Python/sysmodule.c‎

Lines changed: 26 additions & 3 deletions

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