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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>
115 lines
4.3 KiB
ReStructuredText
115 lines
4.3 KiB
ReStructuredText
.. highlight:: c
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.. _weakrefobjects:
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Weak Reference Objects
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----------------------
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Python supports *weak references* as first-class objects. There are two
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specific object types which directly implement weak references. The first is a
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simple reference object, and the second acts as a proxy for the original object
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as much as it can.
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.. c:function:: int PyWeakref_Check(PyObject *ob)
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Return non-zero if *ob* is either a reference or proxy object. This function
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always succeeds.
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.. c:function:: int PyWeakref_CheckRef(PyObject *ob)
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Return non-zero if *ob* is a reference object. This function always succeeds.
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.. c:function:: int PyWeakref_CheckProxy(PyObject *ob)
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Return non-zero if *ob* is a proxy object. This function always succeeds.
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.. c:function:: PyObject* PyWeakref_NewRef(PyObject *ob, PyObject *callback)
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Return a weak reference object for the object *ob*. This will always return
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a new reference, but is not guaranteed to create a new object; an existing
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reference object may be returned. The second parameter, *callback*, can be a
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callable object that receives notification when *ob* is garbage collected; it
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should accept a single parameter, which will be the weak reference object
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itself. *callback* may also be ``None`` or ``NULL``. If *ob* is not a
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weakly referenceable object, or if *callback* is not callable, ``None``, or
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``NULL``, this will return ``NULL`` and raise :exc:`TypeError`.
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.. c:function:: PyObject* PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
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Return a weak reference proxy object for the object *ob*. This will always
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return a new reference, but is not guaranteed to create a new object; an
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existing proxy object may be returned. The second parameter, *callback*, can
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be a callable object that receives notification when *ob* is garbage
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collected; it should accept a single parameter, which will be the weak
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reference object itself. *callback* may also be ``None`` or ``NULL``. If *ob*
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is not a weakly referenceable object, or if *callback* is not callable,
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``None``, or ``NULL``, this will return ``NULL`` and raise :exc:`TypeError`.
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.. c:function:: int PyWeakref_GetRef(PyObject *ref, PyObject **pobj)
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Get a :term:`strong reference` to the referenced object from a weak
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reference, *ref*, into *\*pobj*.
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* On success, set *\*pobj* to a new :term:`strong reference` to the
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referenced object and return 1.
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* If the reference is dead, set *\*pobj* to ``NULL`` and return 0.
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* On error, raise an exception and return -1.
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.. versionadded:: 3.13
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.. c:function:: PyObject* PyWeakref_GetObject(PyObject *ref)
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Return a :term:`borrowed reference` to the referenced object from a weak
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reference, *ref*. If the referent is no longer live, returns ``Py_None``.
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.. note::
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This function returns a :term:`borrowed reference` to the referenced object.
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This means that you should always call :c:func:`Py_INCREF` on the object
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except when it cannot be destroyed before the last usage of the borrowed
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reference.
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.. deprecated-removed:: 3.13 3.15
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Use :c:func:`PyWeakref_GetRef` instead.
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.. c:function:: PyObject* PyWeakref_GET_OBJECT(PyObject *ref)
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Similar to :c:func:`PyWeakref_GetObject`, but does no error checking.
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.. deprecated-removed:: 3.13 3.15
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Use :c:func:`PyWeakref_GetRef` instead.
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.. c:function:: void PyObject_ClearWeakRefs(PyObject *object)
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This function is called by the :c:member:`~PyTypeObject.tp_dealloc` handler
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to clear weak references.
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This iterates through the weak references for *object* and calls callbacks
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for those references which have one. It returns when all callbacks have
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been attempted.
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.. c:function:: void PyUnstable_Object_ClearWeakRefsNoCallbacks(PyObject *object)
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Clears the weakrefs for *object* without calling the callbacks.
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This function is called by the :c:member:`~PyTypeObject.tp_dealloc` handler
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for types with finalizers (i.e., :meth:`~object.__del__`). The handler for
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those objects first calls :c:func:`PyObject_ClearWeakRefs` to clear weakrefs
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and call their callbacks, then the finalizer, and finally this function to
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clear any weakrefs that may have been created by the finalizer.
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In most circumstances, it's more appropriate to use
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:c:func:`PyObject_ClearWeakRefs` to clear weakrefs instead of this function.
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.. versionadded:: 3.13
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