From e630b64418786dffbb2d4216cc0dbe26bf10bea0 Mon Sep 17 00:00:00 2001
From: Pieter Eendebak <pieter.eendebak@gmail.com>
Date: Fri, 27 Jun 2025 08:56:32 +0200
Subject: [PATCH 1/3] Avoid locks are and refcounts in frozenset operatins

---
 Objects/setobject.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/Objects/setobject.c b/Objects/setobject.c
index 8aa6b0d180907b..cf557d1768ca6f 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -85,6 +85,8 @@ set_lookkey(PySetObject *so, PyObject *key, Py_hash_t hash)
     int probes;
     int cmp;
 
+    int frozenset = PyFrozenSet_CheckExact(so);
+
     while (1) {
         entry = &so->table[i];
         probes = (i + LINEAR_PROBES <= mask) ? LINEAR_PROBES: 0;
@@ -101,9 +103,14 @@ set_lookkey(PySetObject *so, PyObject *key, Py_hash_t hash)
                     && unicode_eq(startkey, key))
                     return entry;
                 table = so->table;
-                Py_INCREF(startkey);
-                cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
-                Py_DECREF(startkey);
+                if (frozenset) {
+                    cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
+                } else {
+                    // incref startkey because it can be removed from the set by the compare
+                    Py_INCREF(startkey);
+                    cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
+                    Py_DECREF(startkey);
+                }
                 if (cmp < 0)
                     return NULL;
                 if (table != so->table || entry->key != startkey)
@@ -2234,10 +2241,16 @@ set_contains_lock_held(PySetObject *so, PyObject *key)
 int
 _PySet_Contains(PySetObject *so, PyObject *key)
 {
+    assert(so);
+
     int rv;
-    Py_BEGIN_CRITICAL_SECTION(so);
-    rv = set_contains_lock_held(so, key);
-    Py_END_CRITICAL_SECTION();
+    if (PyFrozenSet_CheckExact(so)) {
+        rv = set_contains_lock_held(so, key);
+    } else {
+        Py_BEGIN_CRITICAL_SECTION(so);
+        rv = set_contains_lock_held(so, key);
+        Py_END_CRITICAL_SECTION();
+    }
     return rv;
 }
 

From 40d2d2917f66abeb5477d925cbb65a7bd65f5cba Mon Sep 17 00:00:00 2001
From: Pieter Eendebak <pieter.eendebak@gmail.com>
Date: Sun, 29 Jun 2025 22:28:39 +0200
Subject: [PATCH 2/3] avoid table check

---
 Objects/setobject.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/Objects/setobject.c b/Objects/setobject.c
index cf557d1768ca6f..a07aad4134f752 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -105,16 +105,18 @@ set_lookkey(PySetObject *so, PyObject *key, Py_hash_t hash)
                 table = so->table;
                 if (frozenset) {
                     cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
+                    if (cmp < 0)
+                        return NULL;
                 } else {
                     // incref startkey because it can be removed from the set by the compare
                     Py_INCREF(startkey);
                     cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
                     Py_DECREF(startkey);
+                    if (cmp < 0)
+                        return NULL;
+                    if (table != so->table || entry->key != startkey)
+                        return set_lookkey(so, key, hash);
                 }
-                if (cmp < 0)
-                    return NULL;
-                if (table != so->table || entry->key != startkey)
-                    return set_lookkey(so, key, hash);
                 if (cmp > 0)
                     return entry;
                 mask = so->mask;

From 10aed735ea78e47731ce6c9a1ff0dd3df14d5fe8 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Wed, 9 Jul 2025 21:27:18 +0000
Subject: [PATCH 3/3] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../2025-07-09-21-27-14.gh-issue-132657.kSA8R3.rst               | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2025-07-09-21-27-14.gh-issue-132657.kSA8R3.rst

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-07-09-21-27-14.gh-issue-132657.kSA8R3.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-07-09-21-27-14.gh-issue-132657.kSA8R3.rst
new file mode 100644
index 00000000000000..99f7a990875a0a
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-07-09-21-27-14.gh-issue-132657.kSA8R3.rst
@@ -0,0 +1 @@
+Improve performance of :class:`frozenset` by removing locks in the free-threading build.