GH-132657: Add lock-free set contains implementation

Include/internal/pycore_pyatomic_ft_wrappers.h

@@ -55,6 +55,8 @@ extern "C" {
     _Py_atomic_store_uintptr_release(&value, new_value)
 #define FT_ATOMIC_STORE_SSIZE_RELAXED(value, new_value) \
     _Py_atomic_store_ssize_relaxed(&value, new_value)
+#define FT_ATOMIC_STORE_SSIZE_RELEASE(value, new_value) \
+    _Py_atomic_store_ssize_release(&value, new_value)
 #define FT_ATOMIC_STORE_UINT8_RELAXED(value, new_value) \
     _Py_atomic_store_uint8_relaxed(&value, new_value)
 #define FT_ATOMIC_STORE_UINT16_RELAXED(value, new_value) \
@@ -133,6 +135,7 @@ extern "C" {
 #define FT_ATOMIC_STORE_PTR_RELEASE(value, new_value) value = new_value
 #define FT_ATOMIC_STORE_UINTPTR_RELEASE(value, new_value) value = new_value
 #define FT_ATOMIC_STORE_SSIZE_RELAXED(value, new_value) value = new_value
+#define FT_ATOMIC_STORE_SSIZE_RELEASE(value, new_value) value = new_value
 #define FT_ATOMIC_STORE_UINT8_RELAXED(value, new_value) value = new_value
 #define FT_ATOMIC_STORE_UINT16_RELAXED(value, new_value) value = new_value
 #define FT_ATOMIC_STORE_UINT32_RELAXED(value, new_value) value = new_value

Lib/test/test_free_threading/test_set.py

@@ -36,6 +36,70 @@ def repr_set():
             for set_repr in set_reprs:
                 self.assertIn(set_repr, ("set()", "{1, 2, 3, 4, 5, 6, 7, 8}"))
 
+    def test_contains_mutate(self):
+        """Test set contains operation combined with mutation."""
+        barrier = Barrier(2)
+        s = set()
+        done = False
+
+        NUM_ITEMS = 2_000
+        NUM_LOOPS = 20
+
+        def read_set():
+            barrier.wait()
+            while not done:
+                for i in range(NUM_ITEMS):
+                    item = i >> 1
+                    result = item in s
+
+        def mutate_set():
+            nonlocal done
+            barrier.wait()
+            for i in range(NUM_LOOPS):
+                s.clear()
+                for j in range(NUM_ITEMS):
+                    s.add(j)
+                for j in range(NUM_ITEMS):
+                    s.discard(j)
+                # executes the set_swap_bodies() function
+                s.__iand__(set(k for k in range(10, 20)))
+            done = True
+
+        threads = [Thread(target=read_set), Thread(target=mutate_set)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+    def test_contains_frozenset(self):
+        barrier = Barrier(3)
+        done = False
+
+        NUM_ITEMS = 2_000
+        NUM_LOOPS = 20
+
+        s = frozenset()
+        def make_set():
+            nonlocal s
+            barrier.wait()
+            while not done:
+                s = frozenset(range(NUM_ITEMS))
+
+        def read_set():
+            nonlocal done
+            barrier.wait()
+            for _ in range(NUM_LOOPS):
+                for i in range(NUM_ITEMS):
+                    item = i >> 1
+                    result = item in s
+            done = True
+
+        threads = [Thread(target=read_set), Thread(target=read_set), Thread(target=make_set)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Core_and_Builtins/2025-07-11-19-57-27.gh-issue-132657.vwDuO2.rst

@@ -0,0 +1,2 @@
+For the free-threaded build, avoid locking the :class:`set` object for the
+``__contains__`` method.