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Described responsibilty of weakly referenced extension types to initialize

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the weakreflist to NULL in the constructor and to fill the tp_flags
slot with Py_TPFLAGS_HAVE_WEAKREFS.  Closes SF bug 586583.
This commit is contained in:
Raymond Hettinger 2002-08-07 16:18:54 +00:00
parent 861bb02448
commit 22c001bd29
1 changed files with 23 additions and 2 deletions
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25
Doc/lib/libweakref.tex
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@ -217,7 +217,9 @@ For an object to be weakly referencable, the extension must include a
weak reference mechanism; it must be initialized to \NULL{} by the weak reference mechanism; it must be initialized to \NULL{} by the
object's constructor. It must also set the \member{tp_weaklistoffset} object's constructor. It must also set the \member{tp_weaklistoffset}
field of the corresponding type object to the offset of the field. field of the corresponding type object to the offset of the field.
For example, the instance type is defined with the following structure: Also, it needs to add \constant{Py_TPFLAGS_HAVE_WEAKREFS} to the
tp_flags slot. For example, the instance type is defined with the
following structure:
\begin{verbatim} \begin{verbatim}
typedef struct { typedef struct {
@ -238,10 +240,29 @@ PyTypeObject PyInstance_Type = {
/* Lots of stuff omitted for brevity... */ /* Lots of stuff omitted for brevity... */
offsetof(PyInstanceObject, in_weakreflist) /* tp_weaklistoffset */ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_WEAKREFS /* tp_flags */
0, /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
offsetof(PyInstanceObject, in_weakreflist), /* tp_weaklistoffset */
}; };
\end{verbatim} \end{verbatim}
The type constructor is responsible for initializing the weak reference
list to \NULL:
\begin{verbatim}
static PyObject *
instance_new() {
/* Other initialization stuff omitted for brevity */
self->in_weakreflist = NULL;
return (PyObject *) self;
}
\end{verbatim}
The only further addition is that the destructor needs to call the The only further addition is that the destructor needs to call the
weak reference manager to clear any weak references. This should be weak reference manager to clear any weak references. This should be
done before any other parts of the destruction have occurred, but is done before any other parts of the destruction have occurred, but is