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>
In the free threaded build, the `_PyObject_LookupSpecial()` call can lead to
reference count contention on the returned function object becuase it
doesn't use stackrefs. Refactor some of the callers to use
`_PyObject_MaybeCallSpecialNoArgs`, which uses stackrefs internally.
This fixes the scaling bottleneck in the "lookup_special" microbenchmark
in `ftscalingbench.py`. However, the are still some uses of
`_PyObject_LookupSpecial()` that need to be addressed in future PRs.
* Add location information when accessing already closed stackref
* Add #def option to track closed stackrefs to provide precise information for use after free and double frees.
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
Fix a few thread-safety bugs to enable test_opcache when run with TSAN:
* Use relaxed atomics when clearing `ht->_spec_cache.getitem`
(gh-115999)
* Add temporary suppression for type slot modifications (gh-127266)
* Use atomic load when reading `*dictptr`
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>
Objects may be temporarily "resurrected" in destructors when calling
finalizers or watcher callbacks. We previously undid the resurrection
by decrementing the reference count using `Py_SET_REFCNT`. This was not
thread-safe because other threads might be accessing the object
(modifying its reference count) if it was exposed by the finalizer,
watcher callback, or temporarily accessed by a racy dictionary or list
access.
This adds internal-only thread-safe functions for temporary object
resurrection during destructors.
This is a precursor to the actual fix for gh-114940, where we will change these macros to use the new lock. This change is almost entirely mechanical; the exceptions are the loops in codeobject.c and ceval.c, which now hold the "head" lock. Note that almost all of the uses of _Py_FOR_EACH_TSTATE_UNLOCKED() here will change to _Py_FOR_EACH_TSTATE_BEGIN() once we add the new per-interpreter lock.
They used to be shared, before 3.12. Returning to sharing them resolves a failure on Py_TRACE_REFS builds.
Co-authored-by: Petr Viktorin <encukou@gmail.com>
This is essentially a cleanup, moving a handful of API declarations to the header files where they fit best, creating new ones when needed.
We do the following:
* add pycore_debug_offsets.h and move _Py_DebugOffsets, etc. there
* inline struct _getargs_runtime_state and struct _gilstate_runtime_state in _PyRuntimeState
* move struct _reftracer_runtime_state to the existing pycore_object_state.h
* add pycore_audit.h and move to it _Py_AuditHookEntry , _PySys_Audit(), and _PySys_ClearAuditHooks
* add audit.h and cpython/audit.h and move the existing audit-related API there
*move the perfmap/trampoline API from cpython/sysmodule.h to cpython/ceval.h, and remove the now-empty cpython/sysmodule.h
Fix a crash caused by immortal interned strings being shared between
sub-interpreters that use basic single-phase init. In that case, the string
can be used by an interpreter that outlives the interpreter that created and
interned it. For interpreters that share obmalloc state, also share the
interned dict with the main interpreter.
This is an un-revert of gh-124646 that then addresses the Py_TRACE_REFS
failures identified by gh-124785.
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 refactors asyncio to use the common freelist helper functions and
macros. As a side effect, the freelist for _asyncio.Future is now
re-enabled in the free-threaded build.
