We replace _PyRuntime.tstate_current with a thread-local variable. As part of this change, we add a _Py_thread_local macro in pyport.h (only for the core runtime) to smooth out the compiler differences. The main motivation here is in support of a per-interpreter GIL, but this change also provides some performance improvement opportunities.
Note that we do not provide a fallback to the thread-local, either falling back to the old tstate_current or to thread-specific storage (PyThread_tss_*()). If that proves problematic then we can circle back. I consider it unlikely, but will run the buildbots to double-check.
Also note that this does not change any of the code related to the GILState API, where it uses a thread state stored in thread-specific storage. I suspect we can combine that with _Py_tss_tstate (from here). However, that can be addressed separately and is not urgent (nor critical).
(While this change was mostly done independently, I did take some inspiration from earlier (~2020) work by @markshannon (main...markshannon:threadstate_in_tls) and @vstinner (#23976).)
This is the implementation of PEP683
Motivation:
The PR introduces the ability to immortalize instances in CPython which bypasses reference counting. Tagging objects as immortal allows up to skip certain operations when we know that the object will be around for the entire execution of the runtime.
Note that this by itself will bring a performance regression to the runtime due to the extra reference count checks. However, this brings the ability of having truly immutable objects that are useful in other contexts such as immutable data sharing between sub-interpreters.
The Py_CLEAR(), Py_SETREF() and Py_XSETREF() macros now only evaluate
their arguments once. If an argument has side effects, these side
effects are no longer duplicated.
Use temporary variables to avoid duplicating side effects of macro
arguments. If available, use _Py_TYPEOF() to avoid type punning.
Otherwise, use memcpy() for the assignment to prevent a
miscompilation with strict aliasing caused by type punning.
Add _Py_TYPEOF() macro: __typeof__() on GCC and clang.
Add test_py_clear() and test_py_setref() unit tests to _testcapi.
Add C++ overloads for _Py_CAST_impl() to handle 0/NULL. This will allow
C++ extensions that pass 0 or NULL to macros using _Py_CAST() to
continue to compile. Without this, you get an error like:
invalid ‘static_cast’ from type ‘int’ to type ‘_object*’
The modern way to use a NULL value in C++ is to use nullptr. However,
we want to not break extensions that do things the old way.
Co-authored-by: serge-sans-paille
Python now always use the ``%zu`` and ``%zd`` printf formats to
format a size_t or Py_ssize_t number. Building Python 3.12 requires a
C11 compiler, so these printf formats are now always supported.
* PyObject_Print() and _PyObject_Dump() now use the printf %zd format
to display an object reference count.
* Update PY_FORMAT_SIZE_T comment.
* Remove outdated notes about the %zd format in PyBytes_FromFormat()
and PyUnicode_FromFormat() documentations.
* configure no longer checks for the %zd format and no longer defines
PY_FORMAT_SIZE_T macro in pyconfig.h.
* pymacconfig.h no longer undefines PY_FORMAT_SIZE_T: macOS 10.4 is
no longer supported. Python 3.12 now requires macOS 10.6 (Snow
Leopard) or newer.
Fix C++ compiler warnings: "zero as null pointer constant"
(clang -Wzero-as-null-pointer-constant).
* Add the _Py_NULL macro used by static inline functions to use
nullptr in C++.
* Replace NULL with nullptr in _testcppext.cpp.
Fix C++ compiler warnings on cast macros, like _PyObject_CAST(), when
casting a constant expression to a non constant type: use
const_cast<> in C++.
* In C++, Py_SAFE_DOWNCAST() now uses static_cast<> rather than
reinterpret_cast<>.
* Add tests to the _testcppext C++ extension.
* test_cppext no longer captures stdout in verbose mode.
Fix C++ compiler warnings about "old-style cast"
(g++ -Wold-style-cast) in the Python C API. Use C++
reinterpret_cast<> and static_cast<> casts when the Python C API is
used in C++.
Example of fixed warning:
Include/object.h:107:43: error: use of old-style cast to
‘PyObject*’ {aka ‘struct _object*’} [-Werror=old-style-cast]
#define _PyObject_CAST(op) ((PyObject*)(op))
Add _Py_reinterpret_cast() and _Py_static_cast() macros.
Remove the HAVE_PY_SET_53BIT_PRECISION macro (moved to the internal
C API).
* Move HAVE_PY_SET_53BIT_PRECISION macro to pycore_pymath.h.
* Replace PY_NO_SHORT_FLOAT_REPR macro with _PY_SHORT_FLOAT_REPR
macro which is always defined. gcc -Wundef emits a warning when
using _PY_SHORT_FLOAT_REPR but the macro is not defined, if
pycore_pymath.h include was forgotten.
The Python 3.11 limited C API no longer includes stdlib.h, stdio.h,
string.h and errno.h.
* Exclude Py_MEMCPY() from Python 3.11 limited C API.
* xxlimited C extension is now built with Python 3.11 limited C API.
Move the following macros , to pycore_pymath.h (internal C API):
* _Py_SET_53BIT_PRECISION_HEADER
* _Py_SET_53BIT_PRECISION_START
* _Py_SET_53BIT_PRECISION_END
PEP 7: add braces to if and "do { ... } while (0)" in these macros.
Move also _Py_get_387controlword() and _Py_set_387controlword()
definitions to pycore_pymath.h. These functions are no longer
exported.
pystrtod.c now includes pycore_pymath.h.
* Move limits.h include and UCHAR_MAX checks to pyport.h.
* Move sanitizers macros to pyport.h.
* Remove comment about <assert.h>: C extensions are built with NDEBUG
automatically by Python.
Remove the following math macros using the errno variable:
* Py_ADJUST_ERANGE1()
* Py_ADJUST_ERANGE2()
* Py_OVERFLOWED()
* Py_SET_ERANGE_IF_OVERFLOW()
* Py_SET_ERRNO_ON_MATH_ERROR()
Create pycore_pymath.h internal header file.
Rename Py_ADJUST_ERANGE1() and Py_ADJUST_ERANGE2() to
_Py_ADJUST_ERANGE1() and _Py_ADJUST_ERANGE2(), and convert these
macros to static inline functions.
Move the following macros to pycore_pymath.h:
* _Py_IntegralTypeSigned()
* _Py_IntegralTypeMax()
* _Py_IntegralTypeMin()
* _Py_InIntegralTypeRange()
Add the Py_ALWAYS_INLINE macro to ask the compiler to always inline a
static inline function. The compiler can ignore it and decides to not
inline the function.
As part of the PEP-652 implementation, I'll tighten the CI check
for functions/data defined with `Py_LIMITED_API`.
Discussion in https://discuss.python.org/t/pep-652-maintaining-the-stable-abi/6986
suggests that parsing C headers is OK (though personally I'd rather generate it...),
but writing a full C parser is a monumental task and adding an existing one as a
dependency brings too many vendoring/bootstraping issues.
So, for the check I'll use a "simple" regex on preprocessor output, and adapt
the few trivial places where the regex won't work.
- Keep declarations in the limited API to one item per line
- Make it possible to override `_Py_NO_RETURN`, so the annotation can be
removed from preprocessor output.
https://bugs.python.org/issue43795
Fix building pycore_bitutils.h internal header on old clang version
without __builtin_bswap16() (ex: Xcode 4.6.3 on Mac OS X 10.7).
Add a new private _Py__has_builtin() macro to check for availability
of a preprocessor builtin function.
Co-Authored-By: Joshua Root <jmr@macports.org>
Co-authored-by: Joshua Root <jmr@macports.org>
If the nl_langinfo(CODESET) function returns an empty string, Python
now uses UTF-8 as the filesystem encoding.
In May 2010 (commit b744ba1d14), I
modified Python to log a warning and use UTF-8 as the filesystem
encoding (instead of None) if nl_langinfo(CODESET) returns an empty
string.
In August 2020 (commit 94908bbc15), I
modified Python startup to fail with a fatal error and a specific
error message if nl_langinfo(CODESET) returns an empty string. The
intent was to prevent guessing the encoding and also investigate user
configuration where this case happens.
In 10 years (2010 to 2020), I saw zero user report about the error
message related to nl_langinfo(CODESET) returning an empty string.
Today, UTF-8 became the defacto standard and it's safe to make the
assumption that the user expects UTF-8. For example,
nl_langinfo(CODESET) can return an empty string on macOS if the
LC_CTYPE locale is not supported, and UTF-8 is the default encoding
on macOS.
While this change is likely to not affect anyone in practice, it
should make UTF-8 lover happy ;-)
Rewrite also the documentation explaining how Python selects the
filesystem encoding and error handler.
The PEP 353, written in 2005, introduced PY_FORMAT_SIZE_T. Python no
longer supports macOS 10.4 and Visual Studio 2010, but requires more
recent macOS and Visual Studio versions. In 2020 with Python 3.10, it
is now safe to use directly "%zu" to format size_t and "%zi" to
format Py_ssize_t.
Add a new internal pycore_byteswap.h header file with the following
functions:
* _Py_bswap16()
* _Py_bswap32()
* _Py_bswap64()
Use these functions in _ctypes, sha256 and sha512 modules,
and also use in the UTF-32 encoder.
sha256, sha512 and _ctypes modules are now built with the internal
C API.
Victor Stinner
Petr Viktorin
Eric Snow
Eddie Elizondo
Michael Droettboom
Ayappan Perumal
Neil Schemenauer
serge-sans-paille
Ganesh Kathiresan
neonene
Mark Dickinson
Christian Heimes
Inada Naoki
db3l
Jozef Grajciar
Steve Dower
Zackery Spytz
Batuhan Taskaya
Vinay Sajip
Hai Shi
Victor Stinner