gh-141805: Fix crash after concurrent addition objects with the same hash to set #143815

Original file line number	Diff line number	Diff line change
Expand Up		@@ -1853,6 +1853,7 @@ def test_iter_and_mutate(self):
		list(si)

		def test_merge_and_mutate(self):
	# gh-141805
		class X:
		def __hash__(self):
		return hash(0)
Expand All		@@ -1865,6 +1866,33 @@ def __eq__(self, o):
		s = {0}
		s.update(other)

	def test_hash_collision_concurrent_add(self):
	class X:
	def __hash__(self):
	return 0
	class Y:
	flag = False
	def __hash__(self):
	return 0
	def __eq__(self, other):
	if not self.flag:
	self.flag = True
	s.add(X())
	return self is other

	a = X()
	s = set()
	s.add(a)
	s.add(X())
	s.remove(a)
	# Now the set contains a dummy entry followed by an entry
	# for an object with hash 0.
	s.add(Y())
	# The following operations should not crash.
	repr(s)
	list(s)
	set() \| s


		class TestOperationsMutating:
		"""Regression test for bpo-46615"""
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Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
	Fix crash in :class:`set` when objects with the same hash are concurrently
	added to the set after removing an element with the same hash while the set
	still contains elements with the same hash.

3 changes: 3 additions & 0 deletions Objects/setobject.c

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -308,6 +308,9 @@ set_add_entry_takeref(PySetObject so, PyObject key, Py_hash_t hash)
		found_unused_or_dummy:
		if (freeslot == NULL)
		goto found_unused;
	if (freeslot->hash != -1) {
	goto restart;
	}
		FT_ATOMIC_STORE_SSIZE_RELAXED(so->used, so->used + 1);
		FT_ATOMIC_STORE_SSIZE_RELAXED(freeslot->hash, hash);
		FT_ATOMIC_STORE_PTR_RELEASE(freeslot->key, key);
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