tj-python · pull · Mar 11, 2026 · Mar 11, 2026 · Mar 11, 2026 · Mar 11, 2026
diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
@@ -132,7 +132,9 @@ Tools/c-analyzer/             @ericsnowcurrently
 Tools/check-c-api-docs/       @ZeroIntensity
 
 # Fuzzing
-Modules/_xxtestfuzz/          @ammaraskar
+Modules/_xxtestfuzz/                    @python/fuzzers
+Lib/test/test_xxtestfuzz.py             @python/fuzzers
+.github/workflows/reusable-cifuzz.yml   @python/fuzzers
 
 # Limited C API & Stable ABI
 Doc/c-api/stable.rst          @encukou

diff --git a/Doc/c-api/float.rst b/Doc/c-api/float.rst
@@ -224,11 +224,6 @@ endian processor, or ``0`` on little endian processor.
 Return value: ``0`` if all is OK, ``-1`` if error (and an exception is set,
 most likely :exc:`OverflowError`).
 
-There are two problems on non-IEEE platforms:
-
-* What this does is undefined if *x* is a NaN or infinity.
-* ``-0.0`` and ``+0.0`` produce the same bytes string.
-
 .. c:function:: int PyFloat_Pack2(double x, char *p, int le)
 
    Pack a C double as the IEEE 754 binary16 half-precision format.
@@ -256,9 +251,6 @@ Return value: The unpacked double.  On error, this is ``-1.0`` and
 :c:func:`PyErr_Occurred` is true (and an exception is set, most likely
 :exc:`OverflowError`).
 
-Note that on a non-IEEE platform this will refuse to unpack a bytes string that
-represents a NaN or infinity.
-
 .. c:function:: double PyFloat_Unpack2(const char *p, int le)
 
    Unpack the IEEE 754 binary16 half-precision format as a C double.

diff --git a/Doc/c-api/memory.rst b/Doc/c-api/memory.rst
@@ -204,8 +204,11 @@ The following function sets, modeled after the ANSI C standard, but specifying
 behavior when requesting zero bytes, are available for allocating and releasing
 memory from the Python heap.
 
-The :ref:`default memory allocator <default-memory-allocators>` uses the
-:ref:`pymalloc memory allocator <pymalloc>`.
+In the GIL-enabled build (default build) the
+:ref:`default memory allocator <default-memory-allocators>` uses the
+:ref:`pymalloc memory allocator <pymalloc>`, whereas in the
+:term:`free-threaded build`, the default is the
+:ref:`mimalloc memory allocator <mimalloc>` instead.
 
 .. warning::
 
@@ -215,6 +218,11 @@ The :ref:`default memory allocator <default-memory-allocators>` uses the
 
    The default allocator is now pymalloc instead of system :c:func:`malloc`.
 
+.. versionchanged:: 3.13
+
+   In the :term:`free-threaded <free threading>` build, the default allocator
+   is now :ref:`mimalloc <mimalloc>`.
+
 .. c:function:: void* PyMem_Malloc(size_t n)
 
    Allocates *n* bytes and returns a pointer of type :c:expr:`void*` to the
@@ -340,7 +348,9 @@ memory from the Python heap.
     the :ref:`Customize Memory Allocators <customize-memory-allocators>` section.
 
 The :ref:`default object allocator <default-memory-allocators>` uses the
-:ref:`pymalloc memory allocator <pymalloc>`.
+:ref:`pymalloc memory allocator <pymalloc>`.  In the
+:term:`free-threaded <free threading>` build, the default is the
+:ref:`mimalloc memory allocator <mimalloc>` instead.
 
 .. warning::
 
@@ -420,23 +430,24 @@ Default Memory Allocators
 
 Default memory allocators:
 
-===============================  ====================  ==================  =====================  ====================
-Configuration                    Name                  PyMem_RawMalloc     PyMem_Malloc           PyObject_Malloc
-===============================  ====================  ==================  =====================  ====================
-Release build                    ``"pymalloc"``        ``malloc``          ``pymalloc``           ``pymalloc``
-Debug build                      ``"pymalloc_debug"``  ``malloc`` + debug  ``pymalloc`` + debug   ``pymalloc`` + debug
-Release build, without pymalloc  ``"malloc"``          ``malloc``          ``malloc``             ``malloc``
-Debug build, without pymalloc    ``"malloc_debug"``    ``malloc`` + debug  ``malloc`` + debug     ``malloc`` + debug
-===============================  ====================  ==================  =====================  ====================
+===================================  =======================  ====================  ======================  ======================
+Configuration                        Name                     PyMem_RawMalloc       PyMem_Malloc            PyObject_Malloc
+===================================  =======================  ====================  ======================  ======================
+Release build                        ``"pymalloc"``           ``malloc``            ``pymalloc``            ``pymalloc``
+Debug build                          ``"pymalloc_debug"``     ``malloc`` + debug    ``pymalloc`` + debug    ``pymalloc`` + debug
+Release build, without pymalloc      ``"malloc"``             ``malloc``            ``malloc``              ``malloc``
+Debug build, without pymalloc        ``"malloc_debug"``       ``malloc`` + debug    ``malloc`` + debug      ``malloc`` + debug
+Free-threaded build                  ``"mimalloc"``           ``mimalloc``          ``mimalloc``            ``mimalloc``
+Free-threaded debug build            ``"mimalloc_debug"``     ``mimalloc`` + debug  ``mimalloc`` + debug    ``mimalloc`` + debug
+===================================  =======================  ====================  ======================  ======================
 
 Legend:
 
 * Name: value for :envvar:`PYTHONMALLOC` environment variable.
 * ``malloc``: system allocators from the standard C library, C functions:
   :c:func:`malloc`, :c:func:`calloc`, :c:func:`realloc` and :c:func:`free`.
 * ``pymalloc``: :ref:`pymalloc memory allocator <pymalloc>`.
-* ``mimalloc``: :ref:`mimalloc memory allocator <mimalloc>`.  The pymalloc
-  allocator will be used if mimalloc support isn't available.
+* ``mimalloc``: :ref:`mimalloc memory allocator <mimalloc>`.
 * "+ debug": with :ref:`debug hooks on the Python memory allocators
   <pymem-debug-hooks>`.
 * "Debug build": :ref:`Python build in debug mode <debug-build>`.
@@ -733,9 +744,27 @@ The mimalloc allocator
 
 .. versionadded:: 3.13
 
-Python supports the mimalloc allocator when the underlying platform support is available.
-mimalloc "is a general purpose allocator with excellent performance characteristics.
-Initially developed by Daan Leijen for the runtime systems of the Koka and Lean languages."
+Python supports the `mimalloc <https://github.com/microsoft/mimalloc/>`__
+allocator when the underlying platform support is available.
+mimalloc is a general purpose allocator with excellent performance
+characteristics, initially developed by Daan Leijen for the runtime systems
+of the Koka and Lean languages.
+
+Unlike :ref:`pymalloc <pymalloc>`, which is optimized for small objects (512
+bytes or fewer), mimalloc handles allocations of any size.
+
+In the :term:`free-threaded <free threading>` build, mimalloc is the default
+and **required** allocator for the :c:macro:`PYMEM_DOMAIN_MEM` and
+:c:macro:`PYMEM_DOMAIN_OBJ` domains.  It cannot be disabled in free-threaded
+builds.  The free-threaded build uses per-thread mimalloc heaps, which allows
+allocation and deallocation to proceed without locking in most cases.
+
+In the default (non-free-threaded) build, mimalloc is available but not the
+default allocator.  It can be selected at runtime using
+:envvar:`PYTHONMALLOC`\ ``=mimalloc`` (or ``mimalloc_debug`` to include
+:ref:`debug hooks <pymem-debug-hooks>`).  It can be disabled at build time
+using the :option:`--without-mimalloc` configure option, but this option
+cannot be combined with :option:`--disable-gil`.
 
 tracemalloc C API
 =================

diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
@@ -606,17 +606,18 @@ are always available.  They are listed here in alphabetical order.
    .. warning::
 
       This function executes arbitrary code. Calling it with
-      user-supplied input may lead to security vulnerabilities.
+      untrusted user-supplied input will lead to security vulnerabilities.
 
    The *source* argument is parsed and evaluated as a Python expression
    (technically speaking, a condition list) using the *globals* and *locals*
    mappings as global and local namespace.  If the *globals* dictionary is
    present and does not contain a value for the key ``__builtins__``, a
    reference to the dictionary of the built-in module :mod:`builtins` is
-   inserted under that key before *source* is parsed.  That way you can
-   control what builtins are available to the executed code by inserting your
-   own ``__builtins__`` dictionary into *globals* before passing it to
-   :func:`eval`.  If the *locals* mapping is omitted it defaults to the
+   inserted under that key before *source* is parsed.
+   Overriding ``__builtins__`` can be used to restrict or change the available
+   names, but this is **not** a security mechanism: the executed code can
+   still access all builtins.
+   If the *locals* mapping is omitted it defaults to the
    *globals* dictionary.  If both mappings are omitted, the source is
    executed with the *globals* and *locals* in the environment where
    :func:`eval` is called.  Note, *eval()* will only have access to the
@@ -671,7 +672,7 @@ are always available.  They are listed here in alphabetical order.
    .. warning::
 
       This function executes arbitrary code. Calling it with
-      user-supplied input may lead to security vulnerabilities.
+      untrusted user-supplied input will lead to security vulnerabilities.
 
    This function supports dynamic execution of Python code. *source* must be
    either a string or a code object.  If it is a string, the string is parsed as
@@ -702,9 +703,10 @@ are always available.  They are listed here in alphabetical order.
 
    If the *globals* dictionary does not contain a value for the key
    ``__builtins__``, a reference to the dictionary of the built-in module
-   :mod:`builtins` is inserted under that key.  That way you can control what
-   builtins are available to the executed code by inserting your own
-   ``__builtins__`` dictionary into *globals* before passing it to :func:`exec`.
+   :mod:`builtins` is inserted under that key.
+   Overriding ``__builtins__`` can be used to restrict or change the available
+   names, but this is **not** a security mechanism: the executed code can
+   still access all builtins.
 
    The *closure* argument specifies a closure--a tuple of cellvars.
    It's only valid when the *object* is a code object containing

diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
@@ -3202,6 +3202,10 @@ The conversion types are:
 |            | character in the result.                            |       |
 +------------+-----------------------------------------------------+-------+
 
+For floating-point formats, the result should be correctly rounded to a given
+precision ``p`` of digits after the decimal point.  The rounding mode matches
+that of the :func:`round` builtin.
+
 Notes:
 
 (1)

diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
@@ -1085,6 +1085,13 @@ conflict.
    * ``pymalloc_debug``: same as ``pymalloc`` but also install debug hooks.
    * ``mimalloc_debug``: same as ``mimalloc`` but also install debug hooks.
 
+   .. note::
+
+      In the :term:`free-threaded <free threading>` build, the ``malloc``,
+      ``malloc_debug``, ``pymalloc``, and ``pymalloc_debug`` values are not
+      supported.  Only ``default``, ``debug``, ``mimalloc``, and
+      ``mimalloc_debug`` are accepted.
+
    .. versionadded:: 3.6
 
    .. versionchanged:: 3.7
@@ -1094,12 +1101,13 @@ conflict.
 .. envvar:: PYTHONMALLOCSTATS
 
    If set to a non-empty string, Python will print statistics of the
-   :ref:`pymalloc memory allocator <pymalloc>` every time a new pymalloc object
-   arena is created, and on shutdown.
+   :ref:`pymalloc memory allocator <pymalloc>` or the
+   :ref:`mimalloc memory allocator <mimalloc>` (whichever is in use)
+   every time a new object arena is created, and on shutdown.
 
    This variable is ignored if the :envvar:`PYTHONMALLOC` environment variable
    is used to force the :c:func:`malloc` allocator of the C library, or if
-   Python is configured without ``pymalloc`` support.
+   Python is configured without both ``pymalloc`` and ``mimalloc`` support.
 
    .. versionchanged:: 3.6
       This variable can now also be used on Python compiled in release mode.

diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst
@@ -774,6 +774,9 @@ also be used to improve performance.
    Disable the fast :ref:`mimalloc <mimalloc>` allocator
    (enabled by default).
 
+   This option cannot be used together with :option:`--disable-gil`
+   because the :term:`free-threaded <free threading>` build requires mimalloc.
+
    See also :envvar:`PYTHONMALLOC` environment variable.
 
 .. option:: --without-pymalloc

diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
@@ -198,6 +198,7 @@ struct _ts {
     _PyStackChunk *datastack_chunk;
     PyObject **datastack_top;
     PyObject **datastack_limit;
+    _PyStackChunk *datastack_cached_chunk;
     /* XXX signal handlers should also be here */
 
     /* The following fields are here to avoid allocation during init.

diff --git a/Include/internal/pycore_floatobject.h b/Include/internal/pycore_floatobject.h
@@ -12,7 +12,6 @@ extern "C" {
 
 /* runtime lifecycle */
 
-extern void _PyFloat_InitState(PyInterpreterState *);
 extern PyStatus _PyFloat_InitTypes(PyInterpreterState *);
 extern void _PyFloat_FiniType(PyInterpreterState *);
 
@@ -42,6 +41,15 @@ extern double _Py_parse_inf_or_nan(const char *p, char **endptr);
 
 extern int _Py_convert_int_to_double(PyObject **v, double *dbl);
 
+/* Should match endianness of the platform in most (all?) cases. */
+
+#ifdef DOUBLE_IS_BIG_ENDIAN_IEEE754
+#  define _PY_FLOAT_BIG_ENDIAN 1
+#  define _PY_FLOAT_LITTLE_ENDIAN 0
+#else
+#  define _PY_FLOAT_BIG_ENDIAN 0
+#  define _PY_FLOAT_LITTLE_ENDIAN 1
+#endif
 
 #ifdef __cplusplus
 }

diff --git a/Include/internal/pycore_pymath.h b/Include/internal/pycore_pymath.h
@@ -182,8 +182,7 @@ extern void _Py_set_387controlword(unsigned short);
 //     (extended precision), and we don't know how to change
 //     the rounding precision.
 #if !defined(DOUBLE_IS_LITTLE_ENDIAN_IEEE754) && \
-    !defined(DOUBLE_IS_BIG_ENDIAN_IEEE754) && \
-    !defined(DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754)
+    !defined(DOUBLE_IS_BIG_ENDIAN_IEEE754)
 #  define _PY_SHORT_FLOAT_REPR 0
 #endif
 

diff --git a/Include/internal/pycore_runtime_init.h b/Include/internal/pycore_runtime_init.h
@@ -13,7 +13,7 @@ extern "C" {
 #include "pycore_debug_offsets.h"  // _Py_DebugOffsets_INIT()
 #include "pycore_dtoa.h"          // _dtoa_state_INIT()
 #include "pycore_faulthandler.h"  // _faulthandler_runtime_state_INIT
-#include "pycore_floatobject.h"   // _py_float_format_unknown
+#include "pycore_floatobject.h"   // _py_float_format_*
 #include "pycore_function.h"
 #include "pycore_hamt.h"          // _PyHamt_BitmapNode_Type
 #include "pycore_import.h"        // IMPORTS_INIT
@@ -84,10 +84,6 @@ extern PyTypeObject _PyExc_MemoryError;
         .stoptheworld = { \
             .is_global = 1, \
         }, \
-        .float_state = { \
-            .float_format = _py_float_format_unknown, \
-            .double_format = _py_float_format_unknown, \
-        }, \
         .types = { \
             .next_version_tag = _Py_TYPE_VERSION_NEXT, \
         }, \
@@ -233,4 +229,4 @@ extern PyTypeObject _PyExc_MemoryError;
 #ifdef __cplusplus
 }
 #endif
-#endif /* !Py_INTERNAL_RUNTIME_INIT_H */
+#endif /* !Py_INTERNAL_RUNTIME_INIT_H */
diff --git a/Include/internal/pycore_runtime_structs.h b/Include/internal/pycore_runtime_structs.h
@@ -35,17 +35,6 @@ struct _pymem_allocators {
     PyObjectArenaAllocator obj_arena;
 };
 
-enum _py_float_format_type {
-    _py_float_format_unknown,
-    _py_float_format_ieee_big_endian,
-    _py_float_format_ieee_little_endian,
-};
-
-struct _Py_float_runtime_state {
-    enum _py_float_format_type float_format;
-    enum _py_float_format_type double_format;
-};
-
 struct pyhash_runtime_state {
     struct {
 #ifndef MS_WINDOWS
@@ -270,7 +259,6 @@ struct pyruntimestate {
     } audit_hooks;
 
     struct _py_object_runtime_state object_state;
-    struct _Py_float_runtime_state float_state;
     struct _Py_unicode_runtime_state unicode_state;
     struct _types_runtime_state types;
     struct _Py_time_runtime_state time;

diff --git a/Include/pymacconfig.h b/Include/pymacconfig.h
@@ -18,7 +18,6 @@
 #undef SIZEOF_UINTPTR_T
 #undef SIZEOF_PTHREAD_T
 #undef WORDS_BIGENDIAN
-#undef DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754
 #undef DOUBLE_IS_BIG_ENDIAN_IEEE754
 #undef DOUBLE_IS_LITTLE_ENDIAN_IEEE754
 #undef HAVE_GCC_ASM_FOR_X87

diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py
@@ -1085,14 +1085,22 @@ def wait(object_list, timeout=None):
 
         Returns list of those objects in object_list which are ready/readable.
         '''
+        object_list = list(object_list)
+
+        if not object_list:
+            if timeout is None:
+                while True:
+                    time.sleep(1e6)
+            elif timeout > 0:
+                time.sleep(timeout)
+            return []
+
         if timeout is None:
             timeout = INFINITE
         elif timeout < 0:
             timeout = 0
         else:
             timeout = int(timeout * 1000 + 0.5)
-
-        object_list = list(object_list)
         waithandle_to_obj = {}
         ov_list = []
         ready_objects = set()