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

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Merged
merged 3 commits into from
Apr 12, 2025
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[3.13] gh-132213: use relaxed atomics for set hash #132447

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c897d92
gh-132013: use relaxed atomics in hash of frozenset (#132014)
kumaraditya303 Apr 2, 2025
3a5b4e3
gh-132213: use relaxed atomics for set hash (#132215)
kumaraditya303 Apr 7, 2025
790081a
revert comment
kumaraditya303 Apr 12, 2025
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41 changes: 27 additions & 14 deletions Objects/setobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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.

Expand Down Expand Up @@ -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;
}

Expand Down Expand Up @@ -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);
}
}

Expand Down Expand Up @@ -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:
Expand Down
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