bpo-25782: avoid hang in PyErr_SetObject when current exception has a cycle in its context chain (GH-27626)
Co-authored-by: Dennis Sweeney 36520290+sweeneyde@users.noreply.github.com
(cherry picked from commit d5c217475c4957a8084ac3f92ae012ece5edc7cb)
Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 339801e..f50a246 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -953,6 +953,148 @@ def __del__(self):
pass
self.assertEqual(e, (None, None, None))
+ def test_raise_does_not_create_context_chain_cycle(self):
+ class A(Exception):
+ pass
+ class B(Exception):
+ pass
+ class C(Exception):
+ pass
+
+ # Create a context chain:
+ # C -> B -> A
+ # Then raise A in context of C.
+ try:
+ try:
+ raise A
+ except A as a_:
+ a = a_
+ try:
+ raise B
+ except B as b_:
+ b = b_
+ try:
+ raise C
+ except C as c_:
+ c = c_
+ self.assertIsInstance(a, A)
+ self.assertIsInstance(b, B)
+ self.assertIsInstance(c, C)
+ self.assertIsNone(a.__context__)
+ self.assertIs(b.__context__, a)
+ self.assertIs(c.__context__, b)
+ raise a
+ except A as e:
+ exc = e
+
+ # Expect A -> C -> B, without cycle
+ self.assertIs(exc, a)
+ self.assertIs(a.__context__, c)
+ self.assertIs(c.__context__, b)
+ self.assertIsNone(b.__context__)
+
+ def test_no_hang_on_context_chain_cycle1(self):
+ # See issue 25782. Cycle in context chain.
+
+ def cycle():
+ try:
+ raise ValueError(1)
+ except ValueError as ex:
+ ex.__context__ = ex
+ raise TypeError(2)
+
+ try:
+ cycle()
+ except Exception as e:
+ exc = e
+
+ self.assertIsInstance(exc, TypeError)
+ self.assertIsInstance(exc.__context__, ValueError)
+ self.assertIs(exc.__context__.__context__, exc.__context__)
+
+ def test_no_hang_on_context_chain_cycle2(self):
+ # See issue 25782. Cycle at head of context chain.
+
+ class A(Exception):
+ pass
+ class B(Exception):
+ pass
+ class C(Exception):
+ pass
+
+ # Context cycle:
+ # +-----------+
+ # V |
+ # C --> B --> A
+ with self.assertRaises(C) as cm:
+ try:
+ raise A()
+ except A as _a:
+ a = _a
+ try:
+ raise B()
+ except B as _b:
+ b = _b
+ try:
+ raise C()
+ except C as _c:
+ c = _c
+ a.__context__ = c
+ raise c
+
+ self.assertIs(cm.exception, c)
+ # Verify the expected context chain cycle
+ self.assertIs(c.__context__, b)
+ self.assertIs(b.__context__, a)
+ self.assertIs(a.__context__, c)
+
+ def test_no_hang_on_context_chain_cycle3(self):
+ # See issue 25782. Longer context chain with cycle.
+
+ class A(Exception):
+ pass
+ class B(Exception):
+ pass
+ class C(Exception):
+ pass
+ class D(Exception):
+ pass
+ class E(Exception):
+ pass
+
+ # Context cycle:
+ # +-----------+
+ # V |
+ # E --> D --> C --> B --> A
+ with self.assertRaises(E) as cm:
+ try:
+ raise A()
+ except A as _a:
+ a = _a
+ try:
+ raise B()
+ except B as _b:
+ b = _b
+ try:
+ raise C()
+ except C as _c:
+ c = _c
+ a.__context__ = c
+ try:
+ raise D()
+ except D as _d:
+ d = _d
+ e = E()
+ raise e
+
+ self.assertIs(cm.exception, e)
+ # Verify the expected context chain cycle
+ self.assertIs(e.__context__, d)
+ self.assertIs(d.__context__, c)
+ self.assertIs(c.__context__, b)
+ self.assertIs(b.__context__, a)
+ self.assertIs(a.__context__, c)
+
def test_unicode_change_attributes(self):
# See issue 7309. This was a crasher.