Sync pre-release CPython 3.15 branch from GitHub (2026-05-23)

Summary:
Imported python/cpython `3.15.0b1+` from upstream rev [`6b17d1a`](https://www.github.com/python/cpython/commit/6b17d1a783d3c0a9c8a35a94e24a2987807728ef) (committed 2026-05-23 19:27:27+00:00).

# Commit Info

Base: (`3.15.0b1+`) - [`081187f`](https://www.github.com/python/cpython/commit/081187f169556fb1b2d6a9b96f7b7e509f6ad985) (commit date: 2026-05-22 21:17:51+00:00)
Imported: (`3.15.0b1+`) - [`6b17d1a`](https://www.github.com/python/cpython/commit/6b17d1a783d3c0a9c8a35a94e24a2987807728ef) (commit date: 2026-05-23 19:27:27+00:00)

# Noteworthy file changes

- Test files (1 added)
- Low-signal files (3 added, 1 removed) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GCXAlScs9nb4-loLAKsnFTfay4lGbr0LAAAz

Differential Revision: D106216755

fbshipit-source-id: 67a13bc4c6172bfa45517af71bc30af0e62f89ea

Author: generatedunixname1734921407115435

Doc/library/threading.rst

@@ -515,7 +515,7 @@ since it is impossible to detect the termination of alien threads.
    This constructor should always be called with keyword arguments.  Arguments
    are:
 
-   *group* should be ``None``; reserved for future extension when a
+   *group* must be ``None`` as it is reserved for future extension when a
    :class:`!ThreadGroup` class is implemented.
 
    *target* is the callable object to be invoked by the :meth:`run` method.

Lib/profiling/sampling/_flamegraph_assets/flamegraph.js

@@ -7,6 +7,7 @@ let invertedData = null;
 let currentThreadFilter = 'all';
 let isInverted = false;
 let useModuleNames = true;
+let zoomedNodeValue = null;
 
 // Heat colors are now defined in CSS variables (--heat-1 through --heat-8)
 // and automatically switch with theme changes - no JS color arrays needed!
@@ -316,6 +317,7 @@ function createPythonTooltip(data) {
     const selfSamples = d.data.self || 0;
     const selfMs = (selfSamples / 1000).toFixed(2);
     const percentage = ((d.data.value / data.value) * 100).toFixed(2);
+    const relativePercentage = Math.min(100, ((d.data.value / (zoomedNodeValue ?? data.value)) * 100)).toFixed(2);
     const calls = d.data.calls || 0;
     const childCount = d.children ? d.children.length : 0;
     const source = d.data.source;
@@ -439,6 +441,11 @@ function createPythonTooltip(data) {
         <span class="tooltip-stat-label">Percentage:</span>
         <span class="tooltip-stat-value accent">${percentage}%</span>
 
+        ${relativePercentage != percentage && relativePercentage != "100.00" ? `
+          <span class="tooltip-stat-label">Relative Percentage:</span>
+          <span class="tooltip-stat-value accent">${relativePercentage}%</span>
+        ` : ''}
+
         ${calls > 0 ? `
           <span class="tooltip-stat-label">Function Calls:</span>
           <span class="tooltip-stat-value">${calls.toLocaleString()}</span>
@@ -620,6 +627,9 @@ function createFlamegraph(tooltip, rootValue, data) {
       const percentage = d.data.value / rootValue;
       const level = getHeatLevel(percentage);
       return heatColors[level];
+    })
+    .onClick(function (d) {
+      zoomedNodeValue = d.data.value;
     });
 
   return chart;
@@ -629,6 +639,7 @@ function renderFlamegraph(chart, data) {
   d3.select("#chart").datum(data).call(chart);
   window.flamegraphChart = chart;
   window.flamegraphData = data;
+  zoomedNodeValue = null;
   populateStats(data);
 }
 
@@ -1269,6 +1280,7 @@ function filterDataByThread(data, threadId) {
 
 function resetZoom() {
   if (window.flamegraphChart) {
+    zoomedNodeValue = null;
     window.flamegraphChart.resetZoom();
   }
 }

Lib/test/test_free_threading/test_pickle.py

@@ -0,0 +1,44 @@
+import pickle
+import threading
+import unittest
+
+from test.support import threading_helper
+
+
+@threading_helper.requires_working_threading()
+class TestPickleFreeThreading(unittest.TestCase):
+
+    def test_pickle_dumps_with_concurrent_dict_mutation(self):
+        # gh-146452: Pickling a dict while another thread mutates it
+        # used to segfault. batch_dict_exact() iterated dict items via
+        # PyDict_Next() which returns borrowed references, and a
+        # concurrent pop/replace could free the value before Py_INCREF
+        # got to it.
+        shared = {str(i): list(range(20)) for i in range(50)}
+
+        def dumper():
+            for _ in range(1000):
+                try:
+                    pickle.dumps(shared)
+                except RuntimeError:
+                    # "dictionary changed size during iteration" is expected
+                    pass
+
+        def mutator():
+            for j in range(1000):
+                key = str(j % 50)
+                shared[key] = list(range(j % 20))
+                if j % 10 == 0:
+                    shared.pop(key, None)
+                    shared[key] = [j]
+
+        threads = []
+        for _ in range(10):
+            threads.append(threading.Thread(target=dumper))
+        threads.append(threading.Thread(target=mutator))
+
+        with threading_helper.start_threads(threads):
+            pass
+
+if __name__ == "__main__":
+    unittest.main()

Lib/test/test_type_cache.py

@@ -1,4 +1,5 @@
 """ Tests for the internal type cache in CPython. """
+import collections.abc
 import dis
 import unittest
 import warnings
@@ -114,6 +115,25 @@ class HolderSub(Holder):
             Holder.set_value()
             HolderSub.value
 
+    def test_abc_register_invalidates_subclass_versions(self):
+        class Parent:
+            pass
+
+        class Child(Parent):
+            pass
+
+        type_assign_version(Parent)
+        type_assign_version(Child)
+        parent_version = type_get_version(Parent)
+        child_version = type_get_version(Child)
+        if parent_version == 0 or child_version == 0:
+            self.skipTest("Could not assign valid type versions")
+
+        collections.abc.Mapping.register(Parent)
+
+        self.assertEqual(type_get_version(Parent), 0)
+        self.assertEqual(type_get_version(Child), 0)
+
 @support.cpython_only
 class TypeCacheWithSpecializationTests(unittest.TestCase):
     def tearDown(self):

Misc/NEWS.d/next/Core_and_Builtins/2026-04-15-15-48-04.gh-issue-148450.2MEVqH.rst

@@ -0,0 +1 @@
+Fix ``abc.register()`` so it invalidates type version tags for registered classes.

Misc/NEWS.d/next/Library/2026-03-26-09-30-00.gh-issue-146452.Y2N6qZ8J.rst

@@ -0,0 +1,2 @@
+Fix segfault in :mod:`pickle` when pickling a dictionary concurrently
+mutated by another thread in the free-threaded build.

Misc/NEWS.d/next/Library/2026-05-18-15-30-34.gh-issue-146452.RM0EVJ.rst

@@ -0,0 +1 @@
+Update the tooltip on the Tachyon flame graph to show both absolute and relative percentages.

Misc/NEWS.d/next/Tools-Demos/2026-05-22-18-51-09.gh-issue-150258.dh8GVK.rst

@@ -1509,7 +1509,9 @@ buffered_iternext(PyObject *op)
         tp == state->PyBufferedRandom_Type)
     {
         /* Skip method call overhead for speed */
+        Py_BEGIN_CRITICAL_SECTION(self);
         line = _buffered_readline(self, -1);
+        Py_END_CRITICAL_SECTION();
     }
     else {
         line = PyObject_CallMethodNoArgs((PyObject *)self,

Modules/_io/bufferedio.c

@@ -3450,12 +3450,9 @@ batch_dict(PickleState *state, PicklerObject *self, PyObject *iter, PyObject *or
  * Returns 0 on success, -1 on error.
  *
  * Note that this currently doesn't work for protocol 0.
-
- * gh-146452: Wrap the dict iteration in a critical sections to prevent
- * concurrent mutation from invalidating PyDict_Next() iteration state.
  */
 static int
-batch_dict_exact(PickleState *state, PicklerObject *self, PyObject *obj)
+batch_dict_exact_impl(PickleState *state, PicklerObject *self, PyObject *obj)
 {
     PyObject *key = NULL, *value = NULL;
     int i;
@@ -3469,24 +3466,15 @@ batch_dict_exact(PickleState *state, PicklerObject *self, PyObject *obj)
     assert(self->proto > 0);
 
     dict_size = PyDict_GET_SIZE(obj);
+    assert(dict_size);
 
     /* Write in batches of BATCHSIZE. */
     Py_ssize_t total = 0;
     do {
         if (dict_size - total == 1) {
-            int next;
-            Py_BEGIN_CRITICAL_SECTION(obj);
-            next = PyDict_Next(obj, &ppos, &key, &value);
-            if (next) {
-                Py_INCREF(key);
-                Py_INCREF(value);
-            }
-            Py_END_CRITICAL_SECTION();
-            if (!next) {
-                PyErr_SetString(PyExc_RuntimeError,
-                                "dictionary changed size during iteration");
-                goto error;
-            }
+            PyDict_Next(obj, &ppos, &key, &value);
+            Py_INCREF(key);
+            Py_INCREF(value);
             if (save(state, self, key, 0) < 0) {
                 goto error;
             }
@@ -3504,18 +3492,9 @@ batch_dict_exact(PickleState *state, PicklerObject *self, PyObject *obj)
         i = 0;
         if (_Pickler_Write(self, &mark_op, 1) < 0)
             return -1;
-        int next;
-        while (1) {
-            Py_BEGIN_CRITICAL_SECTION(obj);
-            next = PyDict_Next(obj, &ppos, &key, &value);
-            if (next) {
-                Py_INCREF(key);
-                Py_INCREF(value);
-            }
-            Py_END_CRITICAL_SECTION();
-            if (!next) {
-                break;
-            }
+        while (PyDict_Next(obj, &ppos, &key, &value)) {
+            Py_INCREF(key);
+            Py_INCREF(value);
             if (save(state, self, key, 0) < 0) {
                 goto error;
             }
@@ -3546,6 +3525,18 @@ batch_dict_exact(PickleState *state, PicklerObject *self, PyObject *obj)
     return -1;
 }
 
+/* gh-146452: Wrap the dict iteration in a critical section to prevent
+   concurrent mutation from invalidating PyDict_Next() iteration state. */
+static int
+batch_dict_exact(PickleState *state, PicklerObject *self, PyObject *obj)
+{
+    int ret;
+    Py_BEGIN_CRITICAL_SECTION(obj);
+    ret = batch_dict_exact_impl(state, self, obj);
+    Py_END_CRITICAL_SECTION();
+    return ret;
+}
+
 static int
 save_dict(PickleState *state, PicklerObject *self, PyObject *obj)
 {