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Original file line number	Diff line number	Diff line change
Expand Up		@@ -42,7 +42,7 @@ PyAPI_FUNC(int) _PyMem_SetDefaultAllocator(
		fills newly allocated memory with CLEANBYTE (0xCD) and newly freed memory
		with DEADBYTE (0xDD). Detect also "untouchable bytes" marked
		with FORBIDDENBYTE (0xFD). */
		static inline int _PyMem_IsPtrFreed(void *ptr)
		static inline int _PyMem_IsPtrFreed(const void *ptr)
		{
		uintptr_t value = (uintptr_t)ptr;
		#if SIZEOF_VOID_P == 8
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34 changes: 33 additions & 1 deletion 34 Lib/test/test_gc.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -1361,6 +1361,34 @@ def __del__(self):
		# empty __dict__.
		self.assertEqual(x, None)


		class PythonFinalizationTests(unittest.TestCase):
		def test_ast_fini(self):
		# bpo-44184: Regression test for subtype_dealloc() when deallocating
		# an AST instance also destroy its AST type: subtype_dealloc() must
		# not access the type memory after deallocating the instance, since
		# the type memory can be freed as well. The test is also related to
		# _PyAST_Fini() which clears references to AST types.
		code = textwrap.dedent("""
		import ast
		import codecs

		# Small AST tree to keep their AST types alive
		tree = ast.parse("def f(x, y): return 2*x-y")
		x = [tree]
		x.append(x)

		# Put the cycle somewhere to survive until the last GC collection.
		# Codec search functions are only cleared at the end of
		# interpreter_clear().
		def search_func(encoding):
		return None
		search_func.a = x
		codecs.register(search_func)
		""")
		assert_python_ok("-c", code)


		def test_main():
		enabled = gc.isenabled()
		gc.disable()
Expand All		@@ -1370,7 +1398,11 @@ def test_main():

		try:
		gc.collect() # Delete 2nd generation garbage
		run_unittest(GCTests, GCTogglingTests, GCCallbackTests)
		run_unittest(
		GCTests,
		GCCallbackTests,
		GCTogglingTests,
		PythonFinalizationTests)
		finally:
		gc.set_debug(debug)
		# test gc.enable() even if GC is disabled by default
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3 changes: 3 additions & 0 deletions 3 Misc/NEWS.d/next/Core and Builtins/2021-05-21-01-42-45.bpo-44184.9qOptC.rst

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Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Fix a crash at Python exit when a deallocator function removes the last strong
		reference to a heap type.
		Patch by Victor Stinner.

11 changes: 9 additions & 2 deletions 11 Objects/typeobject.c

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -1446,15 +1446,22 @@ subtype_dealloc(PyObject *self)
		if (_PyType_IS_GC(base)) {
		_PyObject_GC_TRACK(self);
		}

		// Don't read type memory after calling basedealloc() since basedealloc()
		// can deallocate the type and free its memory.
		int type_needs_decref = (type->tp_flags & Py_TPFLAGS_HEAPTYPE
		&& !(base->tp_flags & Py_TPFLAGS_HEAPTYPE));

		assert(basedealloc);
		basedealloc(self);

		/* Can't reference self beyond this point. It's possible tp_del switched
		our type from a HEAPTYPE to a non-HEAPTYPE, so be careful about
		reference counting. Only decref if the base type is not already a heap
		allocated type. Otherwise, basedealloc should have decref'd it already */
		if (type->tp_flags & Py_TPFLAGS_HEAPTYPE && !(base->tp_flags & Py_TPFLAGS_HEAPTYPE))
		Py_DECREF(type);
		if (type_needs_decref) {
		Py_DECREF(type);
		}

		endlabel:
		Py_TRASHCAN_END
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