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Issue #18112: PEP 442 implementation (safe object finalization).

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Antoine Pitrou 2013-07-30 19:59:21 +02:00
parent c5d95b17ac
commit 796564c27b
25 changed files with 1254 additions and 321 deletions
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24
Doc/extending/newtypes.rst
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@ -157,7 +157,8 @@ to :const:`Py_TPFLAGS_DEFAULT`. ::
Py_TPFLAGS_DEFAULT, /* tp_flags */
All types should include this constant in their flags. It enables all of the
members defined by the current version of Python.
members defined until at least Python 3.3. If you need further members,
you will need to OR the corresponding flags.
We provide a doc string for the type in :attr:`tp_doc`. ::
@ -928,8 +929,9 @@ Finalization and De-allocation
This function is called when the reference count of the instance of your type is
reduced to zero and the Python interpreter wants to reclaim it. If your type
has memory to free or other clean-up to perform, put it here. The object itself
needs to be freed here as well. Here is an example of this function::
has memory to free or other clean-up to perform, you can put it here. The
object itself needs to be freed here as well. Here is an example of this
function::
static void
newdatatype_dealloc(newdatatypeobject * obj)
@ -981,6 +983,22 @@ done. This can be done using the :c:func:`PyErr_Fetch` and
Py_TYPE(obj)->tp_free((PyObject*)self);
}
.. note::
There are limitations to what you can safely do in a deallocator function.
First, if your type supports garbage collection (using :attr:`tp_traverse`
and/or :attr:`tp_clear`), some of the object's members can have been
cleared or finalized by the time :attr:`tp_dealloc` is called. Second, in
:attr:`tp_dealloc`, your object is in an unstable state: its reference
count is equal to zero. Any call to a non-trivial object or API (as in the
example above) might end up calling :attr:`tp_dealloc` again, causing a
double free and a crash.
Starting with Python 3.4, it is recommended not to put any complex
finalization code in :attr:`tp_dealloc`, and instead use the new
:c:member:`~PyTypeObject.tp_finalize` type method.
.. seealso::
:pep:`442` explains the new finalization scheme.
.. index::
single: string; object representation