Sync pre-release CPython 3.15 branch from GitHub (2026-08-22)

Summary:
Imported python/cpython `3.15.0rc1+dev` from upstream rev [`e839679`](https://www.github.com/python/cpython/commit/e8396792a79adeb2dd6fe523b1722fe8ec6e50f7) (committed 2026-08-22 09:41:27+00:00).

# Commit Info

- Base: (`3.15.0rc1+dev`) - [`f71fbc5`](https://www.github.com/python/cpython/commit/f71fbc558a3051781297106f53820b04c217c13d) (commit date: 2026-08-21 01:40:43+00:00)
- Imported: (`3.15.0rc1+dev`) - [`e839679`](https://www.github.com/python/cpython/commit/e8396792a79adeb2dd6fe523b1722fe8ec6e50f7) (commit date: 2026-08-22 09:41:27+00:00)

# Noteworthy file changes

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

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GATlhiA0isQYmQkFAMUtbKmNEENdbr0LAAAz

Differential Revision: D117103754

fbshipit-source-id: a14fa01d6927ebf87b55a52800519d5754ece469

Author: generatedunixname1734921407115435

Doc/library/csv.rst

@@ -314,8 +314,8 @@ The :mod:`!csv` module defines the following classes:
 
       If several delimiters fit the sample equally well ---
       for example if both ``','`` and ``';'`` split every row consistently ---
-      the delimiters ``','``, ``'\t'``, ``';'``, ``' '`` and ``':'``
-      are preferred, in this order,
+      the delimiters listed in the :attr:`~Sniffer.preferred` attribute
+      are preferred, in that order,
       no matter how many times each of them occurs.
 
    .. method:: has_header(sample)
@@ -337,6 +337,15 @@ The :mod:`!csv` module defines the following classes:
       This method is a rough heuristic and may produce both false positives and
       negatives.
 
+   The :class:`Sniffer` class has the following attribute:
+
+   .. attribute:: preferred
+
+      The list of the delimiters preferred for breaking ties,
+      in the order of preference.
+      It can be modified.
+      Its initial value is ``[',', '\t', ';', ' ', ':']``.
+
 An example for :class:`Sniffer` use::
 
    with open('example.csv', newline='') as csvfile:

Include/internal/pycore_code.h

@@ -582,6 +582,10 @@ PyAPI_FUNC(_Py_CODEUNIT *) _PyCode_GetTLBC(PyCodeObject *co);
 // Returns the reserved index or -1 on error.
 extern int32_t _Py_ReserveTLBCIndex(PyInterpreterState *interp);
 
+// Release an index returned by _Py_ReserveTLBCIndex() that was never stored
+// in a PyThreadState.
+extern void _Py_UnreserveTLBCIndex(PyInterpreterState *interp, int32_t index);
+
 // Release the current thread's index into thread-local bytecode arrays
 extern void _Py_ClearTLBCIndex(_PyThreadStateImpl *tstate);
 

Misc/NEWS.d/next/Core_and_Builtins/2026-08-07-13-40-12.gh-issue-155363.Qk3Vt9.rst

@@ -0,0 +1,4 @@
+Fix a leak in the :term:`free-threaded build` when creating a thread state
+fails after an internal QSBR slot has been reserved for it.  The slot could
+never be reclaimed, so the QSBR array grew without bound across repeated
+failures.

Objects/codeobject.c

@@ -3313,14 +3313,20 @@ _Py_ReserveTLBCIndex(PyInterpreterState *interp)
 }
 
 void
-_Py_ClearTLBCIndex(_PyThreadStateImpl *tstate)
+_Py_UnreserveTLBCIndex(PyInterpreterState *interp, int32_t index)
 {
-    PyInterpreterState *interp = ((PyThreadState *)tstate)->interp;
     if (interp->config.tlbc_enabled) {
-        _PyIndexPool_FreeIndex(&interp->tlbc_indices, tstate->tlbc_index);
+        _PyIndexPool_FreeIndex(&interp->tlbc_indices, index);
     }
 }
 
+void
+_Py_ClearTLBCIndex(_PyThreadStateImpl *tstate)
+{
+    PyInterpreterState *interp = ((PyThreadState *)tstate)->interp;
+    _Py_UnreserveTLBCIndex(interp, tstate->tlbc_index);
+}
+
 static _PyCodeArray *
 _PyCodeArray_New(Py_ssize_t size)
 {

Python/pystate.c

@@ -1645,21 +1645,23 @@ new_threadstate(PyInterpreterState *interp, int whence)
         return NULL;
     }
 
-#ifdef Py_GIL_DISABLED
-    Py_ssize_t qsbr_idx = _Py_qsbr_reserve(interp);
-    if (qsbr_idx < 0) {
+#ifdef Py_STATS
+    // The PyStats structure is quite large and is allocated separated from
+    // tstate.
+    if (!_PyStats_ThreadInit(interp, tstate)) {
         free_threadstate(tstate);
         return NULL;
     }
+#endif
+#ifdef Py_GIL_DISABLED
     int32_t tlbc_idx = _Py_ReserveTLBCIndex(interp);
     if (tlbc_idx < 0) {
         free_threadstate(tstate);
         return NULL;
     }
-#endif
-#ifdef Py_STATS
-    // The PyStats structure is quite large and is allocated separated from tstate.
-    if (!_PyStats_ThreadInit(interp, tstate)) {
+    Py_ssize_t qsbr_idx = _Py_qsbr_reserve(interp);
+    if (qsbr_idx < 0) {
+        _Py_UnreserveTLBCIndex(interp, tlbc_idx);
         free_threadstate(tstate);
         return NULL;
     }