[Python-checkins] [3.13] gh-132213: use relaxed atomics for set hash (#132447)

[kumaraditya303]

https://github.com/python/cpython/commit/67b1c765ef4aca61355747f7c7037e75b0c6b87b
commit: 67b1c765ef4aca61355747f7c7037e75b0c6b87b
branch: 3.13
author: Kumar Aditya <kumaradi...@python.org>
committer: kumaraditya303 <kumaradi...@python.org>
date: 2025-04-12T18:20:24Z
summary:

[3.13] gh-132213: use relaxed atomics for set hash  (#132447)

files:
M Objects/setobject.c

diff --git a/Objects/setobject.c b/Objects/setobject.c
index 81a34ad5ab12c5..7c5d6eb34cae08 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -400,7 +400,7 @@ set_empty_to_minsize(PySetObject *so)
     FT_ATOMIC_STORE_SSIZE_RELAXED(so->used, 0);
     so->mask = PySet_MINSIZE - 1;
     so->table = so->smalltable;
-    so->hash = -1;
+    FT_ATOMIC_STORE_SSIZE_RELAXED(so->hash, -1);
 }
 
 static int
@@ -718,18 +718,15 @@ _shuffle_bits(Py_uhash_t h)
    large primes with "interesting bit patterns" and that passed tests
    for good collision statistics on a variety of problematic datasets
    including powersets and graph structures (such as David Eppstein's
-   graph recipes in Lib/test/test_set.py) */
+   graph recipes in Lib/test/test_set.py). */
 
 static Py_hash_t
-frozenset_hash(PyObject *self)
+frozenset_hash_impl(PyObject *self)
 {
-    PySetObject *so = (PySetObject *)self;
+    PySetObject *so = _PySet_CAST(self);
     Py_uhash_t hash = 0;
     setentry *entry;
 
-    if (so->hash != -1)
-        return so->hash;
-
     /* Xor-in shuffled bits from every entry's hash field because xor is
        commutative and a frozenset hash should be independent of order.
 
@@ -762,7 +759,21 @@ frozenset_hash(PyObject *self)
     if (hash == (Py_uhash_t)-1)
         hash = 590923713UL;
 
-    so->hash = hash;
+    return (Py_hash_t)hash;
+}
+
+static Py_hash_t
+frozenset_hash(PyObject *self)
+{
+    PySetObject *so = _PySet_CAST(self);
+    Py_uhash_t hash;
+
+    if (FT_ATOMIC_LOAD_SSIZE_RELAXED(so->hash) != -1) {
+        return FT_ATOMIC_LOAD_SSIZE_RELAXED(so->hash);
+    }
+
+    hash = frozenset_hash_impl(self);
+    FT_ATOMIC_STORE_SSIZE_RELAXED(so->hash, hash);
     return hash;
 }
 
@@ -1202,10 +1213,12 @@ set_swap_bodies(PySetObject *a, PySetObject *b)
 
     if (PyType_IsSubtype(Py_TYPE(a), &PyFrozenSet_Type)  &&
         PyType_IsSubtype(Py_TYPE(b), &PyFrozenSet_Type)) {
-        h = a->hash;     a->hash = b->hash;  b->hash = h;
+        h = FT_ATOMIC_LOAD_SSIZE_RELAXED(a->hash);
+        FT_ATOMIC_STORE_SSIZE_RELAXED(a->hash, 
FT_ATOMIC_LOAD_SSIZE_RELAXED(b->hash));
+        FT_ATOMIC_STORE_SSIZE_RELAXED(b->hash, h);
     } else {
-        a->hash = -1;
-        b->hash = -1;
+        FT_ATOMIC_STORE_SSIZE_RELAXED(a->hash, -1);
+        FT_ATOMIC_STORE_SSIZE_RELAXED(b->hash, -1);
     }
 }
 
@@ -2086,9 +2099,9 @@ set_richcompare(PySetObject *v, PyObject *w, int op)
     case Py_EQ:
         if (PySet_GET_SIZE(v) != PySet_GET_SIZE(w))
             Py_RETURN_FALSE;
-        if (v->hash != -1  &&
-            ((PySetObject *)w)->hash != -1 &&
-            v->hash != ((PySetObject *)w)->hash)
+        Py_hash_t v_hash = FT_ATOMIC_LOAD_SSIZE_RELAXED(v->hash);
+        Py_hash_t w_hash = FT_ATOMIC_LOAD_SSIZE_RELAXED(((PySetObject 
*)w)->hash);
+        if (v_hash != -1 && w_hash != -1 && v_hash != w_hash)
             Py_RETURN_FALSE;
         return set_issubset(v, w);
     case Py_NE:

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