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e8752d7b80
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>
119 lines
3.3 KiB
C
119 lines
3.3 KiB
C
#ifndef Py_INTERNAL_WEAKREF_H
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#define Py_INTERNAL_WEAKREF_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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#ifndef Py_BUILD_CORE
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# error "this header requires Py_BUILD_CORE define"
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#endif
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#include "pycore_critical_section.h" // Py_BEGIN_CRITICAL_SECTION()
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#include "pycore_lock.h"
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#include "pycore_object.h" // _Py_REF_IS_MERGED()
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#include "pycore_pyatomic_ft_wrappers.h"
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#ifdef Py_GIL_DISABLED
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#define WEAKREF_LIST_LOCK(obj) \
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_PyInterpreterState_GET() \
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->weakref_locks[((uintptr_t)obj) % NUM_WEAKREF_LIST_LOCKS]
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// Lock using the referenced object
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#define LOCK_WEAKREFS(obj) \
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PyMutex_LockFlags(&WEAKREF_LIST_LOCK(obj), _Py_LOCK_DONT_DETACH)
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#define UNLOCK_WEAKREFS(obj) PyMutex_Unlock(&WEAKREF_LIST_LOCK(obj))
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// Lock using a weakref
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#define LOCK_WEAKREFS_FOR_WR(wr) \
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PyMutex_LockFlags(wr->weakrefs_lock, _Py_LOCK_DONT_DETACH)
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#define UNLOCK_WEAKREFS_FOR_WR(wr) PyMutex_Unlock(wr->weakrefs_lock)
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#else
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#define LOCK_WEAKREFS(obj)
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#define UNLOCK_WEAKREFS(obj)
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#define LOCK_WEAKREFS_FOR_WR(wr)
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#define UNLOCK_WEAKREFS_FOR_WR(wr)
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#endif
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static inline int _is_dead(PyObject *obj)
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{
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// Explanation for the Py_REFCNT() check: when a weakref's target is part
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// of a long chain of deallocations which triggers the trashcan mechanism,
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// clearing the weakrefs can be delayed long after the target's refcount
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// has dropped to zero. In the meantime, code accessing the weakref will
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// be able to "see" the target object even though it is supposed to be
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// unreachable. See issue gh-60806.
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#if defined(Py_GIL_DISABLED)
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Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&obj->ob_ref_shared);
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return shared == _Py_REF_SHARED(0, _Py_REF_MERGED);
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#else
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return (Py_REFCNT(obj) == 0);
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#endif
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}
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static inline PyObject* _PyWeakref_GET_REF(PyObject *ref_obj)
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{
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assert(PyWeakref_Check(ref_obj));
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PyWeakReference *ref = _Py_CAST(PyWeakReference*, ref_obj);
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PyObject *obj = FT_ATOMIC_LOAD_PTR(ref->wr_object);
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if (obj == Py_None) {
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// clear_weakref() was called
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return NULL;
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}
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LOCK_WEAKREFS(obj);
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#ifdef Py_GIL_DISABLED
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if (ref->wr_object == Py_None) {
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// clear_weakref() was called
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UNLOCK_WEAKREFS(obj);
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return NULL;
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}
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#endif
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if (_Py_TryIncref(obj)) {
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UNLOCK_WEAKREFS(obj);
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return obj;
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}
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UNLOCK_WEAKREFS(obj);
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return NULL;
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}
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static inline int _PyWeakref_IS_DEAD(PyObject *ref_obj)
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{
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assert(PyWeakref_Check(ref_obj));
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int ret = 0;
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PyWeakReference *ref = _Py_CAST(PyWeakReference*, ref_obj);
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PyObject *obj = FT_ATOMIC_LOAD_PTR(ref->wr_object);
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if (obj == Py_None) {
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// clear_weakref() was called
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ret = 1;
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}
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else {
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LOCK_WEAKREFS(obj);
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// See _PyWeakref_GET_REF() for the rationale of this test
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#ifdef Py_GIL_DISABLED
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ret = (ref->wr_object == Py_None) || _is_dead(obj);
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#else
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ret = _is_dead(obj);
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#endif
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UNLOCK_WEAKREFS(obj);
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}
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return ret;
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}
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extern Py_ssize_t _PyWeakref_GetWeakrefCount(PyObject *obj);
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// Clear all the weak references to obj but leave their callbacks uncalled and
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// intact.
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extern void _PyWeakref_ClearWeakRefsNoCallbacks(PyObject *obj);
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PyAPI_FUNC(int) _PyWeakref_IsDead(PyObject *weakref);
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#ifdef __cplusplus
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}
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#endif
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#endif /* !Py_INTERNAL_WEAKREF_H */
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