After gh-130704, the interpreter replaces some uses of `LOAD_FAST` with
`LOAD_FAST_BORROW` which avoid incref/decrefs by "borrowing" references
on the interpreter stack when the bytecode compiler can determine that
it's safe.
This change broke some checks in C API extensions that relied on
`Py_REFCNT()` of `1` to determine if it's safe to modify an object
in-place. Objects may have a reference count of one, but still be
referenced further up the interpreter stack due to borrowing of
references.
This provides a replacement function for those checks.
`PyUnstable_Object_IsUniqueReferencedTemporary` is more conservative:
it checks that the object has a reference count of one and that it exists as a
unique strong reference in the interpreter's stack of temporary
variables in the top most frame.
See also:
* https://github.com/numpy/numpy/issues/28681
Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>
Co-authored-by: T. Wouters <thomas@python.org>
Co-authored-by: mpage <mpage@cs.stanford.edu>
Co-authored-by: Mark Shannon <mark@hotpy.org>
Co-authored-by: Victor Stinner <vstinner@python.org>
This fixes a fairly subtle bug involving finalizers and resurrection in
debug free threaded builds: if `_PyObject_ResurrectEnd` returns `1`
(i.e., the object was resurrected by a finalizer), it's not safe to
access the object because it might still be deallocated. For example:
* The finalizer may have exposed the object to another thread. That
thread may hold the last reference and concurrently deallocate it any
time after `_PyObject_ResurrectEnd()` returns `1`.
* `_PyObject_ResurrectEnd()` may call `_Py_brc_queue_object()`, which
may internally deallocate the object immediately if the owning thread
is dead.
Therefore, it's important not to access the object after it's
resurrected. We only violate this in two cases, and only in debug
builds:
* We assert that the object is tracked appropriately. This is now moved
up betewen the finalizer and the `_PyObject_ResurrectEnd()` call.
* The `--with-trace-refs` builds may need to remember the object if
it's resurrected. This is now handled by `_PyObject_ResurrectStart()`
and `_PyObject_ResurrectEnd()`.
Note that `--with-trace-refs` is currently disabled in `--disable-gil`
builds because the refchain hash table isn't thread-safe, but this
refactoring avoids an additional thread-safety issue.
* Implement C recursion protection with limit pointers for Linux, MacOS and Windows
* Remove calls to PyOS_CheckStack
* Add stack protection to parser
* Make tests more robust to low stacks
* Improve error messages for stack overflow
Revert "GH-91079: Implement C stack limits using addresses, not counters. (GH-130007)" for now
Unfortunatlely, the change broke some buildbots.
This reverts commit 2498c22fa0.
* Implement C recursion protection with limit pointers
* Remove calls to PyOS_CheckStack
* Add stack protection to parser
* Make tests more robust to low stacks
* Improve error messages for stack overflow
This exposes `_Py_TryIncref` as `PyUnstable_TryIncref()` and the helper
function `_PyObject_SetMaybeWeakref` as `PyUnstable_EnableTryIncRef`.
These are helpers for dealing with unowned references in a safe way,
particularly in the free threading build.
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Use per-thread refcounting for the reference from function objects to
their corresponding code object. This can be a source of contention when
frequently creating nested functions. Deferred refcounting alone isn't a
great fit here because these references are on the heap and may be
modified by other libraries.
The free-threaded build partially stores heap type reference counts in
distributed manner in per-thread arrays. This avoids reference count
contention when creating or destroying instances.
Co-authored-by: Ken Jin <kenjin@python.org>
This exposes `PyUnstable_Object_ClearWeakRefsNoCallbacks` as an unstable
C-API function to provide a thread-safe mechanism for clearing weakrefs
without executing callbacks.
Some C-API extensions need to clear weakrefs without calling callbacks,
such as after running finalizers like we do in subtype_dealloc.
Previously they could use `_PyWeakref_ClearRef` on each weakref, but
that's not thread-safe in the free-threaded build.
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Add _PyType_LookupRef and use incref before setting attribute on type
Makes setting an attribute on a class and signaling type modified atomic
Avoid adding re-entrancy exposing the type cache in an inconsistent state by decrefing after type is updated
gh-113750: Fix object resurrection on free-threaded builds
This avoids the undesired re-initializing of fields like `ob_gc_bits`,
`ob_mutex`, and `ob_tid` when an object is resurrected due to its
finalizer being called.
This change has no effect on the default (with GIL) build.
Add PyThreadState_GetUnchecked() function: similar to
PyThreadState_Get(), but don't issue a fatal error if it is NULL. The
caller is responsible to check if the result is NULL. Previously,
this function was private and known as _PyThreadState_UncheckedGet().
Make PyObject_VisitManagedDict() and PyObject_ClearManagedDict()
functions public in Python 3.13 C API.
* Rename _PyObject_VisitManagedDict() to PyObject_VisitManagedDict().
* Rename _PyObject_ClearManagedDict() to PyObject_ClearManagedDict().
* Document these functions.
Remove the private _Py_Identifier type and related private functions
from the public C API:
* _PyObject_GetAttrId()
* _PyObject_LookupSpecialId()
* _PyObject_SetAttrId()
* _PyType_LookupId()
* _Py_IDENTIFIER()
* _Py_static_string()
* _Py_static_string_init()
Move them to the internal C API: add a new pycore_identifier.h header
file. No longer export these functions.
Move private _PyObject and private _PyType functions to the internal
C API (pycore_object.h):
* _PyObject_GetMethod()
* _PyObject_IsAbstract()
* _PyObject_NextNotImplemented()
* _PyType_CalculateMetaclass()
* _PyType_GetDocFromInternalDoc()
* _PyType_GetTextSignatureFromInternalDoc()
No longer export these functions.
Move private debug _PyObject functions to the internal C API
(pycore_object.h):
* _PyDebugAllocatorStats()
* _PyObject_CheckConsistency()
* _PyObject_DebugTypeStats()
* _PyObject_IsFreed()
No longer export most of these functions, except of
_PyObject_IsFreed().
Move test functions using _PyObject_IsFreed() from _testcapi to
_testinternalcapi. check_pyobject_is_freed() test no longer catch
_testcapi.error: the tested function cannot raise _testcapi.error.
