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gh-111926: Set up basic sementics of weakref API for freethreading (gh-113621) 

---------

Co-authored-by: Sam Gross <colesbury@gmail.com>
This commit is contained in:
Donghee Na 2024-01-03 22:25:27 +09:00 committed by GitHub
parent fab7ad62ce
commit 0c3455a969
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1 changed files with 40 additions and 22 deletions
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62
Include/internal/pycore_weakref.h
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@ -9,48 +9,66 @@ extern "C" {
#endif
#include "pycore_critical_section.h" // Py_BEGIN_CRITICAL_SECTION()
#include "pycore_object.h" // _Py_REF_IS_MERGED()
static inline PyObject* _PyWeakref_GET_REF(PyObject *ref_obj) {
assert(PyWeakref_Check(ref_obj));
PyWeakReference *ref = _Py_CAST(PyWeakReference*, ref_obj);
PyObject *obj = ref->wr_object;
if (obj == Py_None) {
// clear_weakref() was called
return NULL;
}
static inline int _is_dead(PyObject *obj)
{
// Explanation for the Py_REFCNT() check: when a weakref's target is part
// of a long chain of deallocations which triggers the trashcan mechanism,
// clearing the weakrefs can be delayed long after the target's refcount
// has dropped to zero. In the meantime, code accessing the weakref will
// be able to "see" the target object even though it is supposed to be
// unreachable. See issue gh-60806.
Py_ssize_t refcnt = Py_REFCNT(obj);
if (refcnt == 0) {
return NULL;
#if defined(Py_GIL_DISABLED)
Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&obj->ob_ref_shared);
return shared == _Py_REF_SHARED(0, _Py_REF_MERGED);
#else
return (Py_REFCNT(obj) == 0);
#endif
}
assert(refcnt > 0);
return Py_NewRef(obj);
}
static inline int _PyWeakref_IS_DEAD(PyObject *ref_obj) {
static inline PyObject* _PyWeakref_GET_REF(PyObject *ref_obj)
{
assert(PyWeakref_Check(ref_obj));
int is_dead;
PyObject *ret = NULL;
Py_BEGIN_CRITICAL_SECTION(ref_obj);
PyWeakReference *ref = _Py_CAST(PyWeakReference*, ref_obj);
PyObject *obj = ref->wr_object;
if (obj == Py_None) {
// clear_weakref() was called
goto end;
}
if (_is_dead(obj)) {
goto end;
}
#if !defined(Py_GIL_DISABLED)
assert(Py_REFCNT(obj) > 0);
#endif
ret = Py_NewRef(obj);
end:
Py_END_CRITICAL_SECTION();
return ret;
}
static inline int _PyWeakref_IS_DEAD(PyObject *ref_obj)
{
assert(PyWeakref_Check(ref_obj));
int ret = 0;
Py_BEGIN_CRITICAL_SECTION(ref_obj);
PyWeakReference *ref = _Py_CAST(PyWeakReference*, ref_obj);
PyObject *obj = ref->wr_object;
if (obj == Py_None) {
// clear_weakref() was called
is_dead = 1;
ret = 1;
}
else {
// See _PyWeakref_GET_REF() for the rationale of this test
is_dead = (Py_REFCNT(obj) == 0);
ret = _is_dead(obj);
}
Py_END_CRITICAL_SECTION();
return is_dead;
return ret;
}
extern Py_ssize_t _PyWeakref_GetWeakrefCount(PyWeakReference *head);