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Allocating a new weakref object can cause existing weakref objects for

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the same object to be collected by the cyclic GC support if they are
only referenced by a cycle.  If the weakref being collected was one of
the weakrefs without callbacks, some local variables for the
constructor became invalid and have to be re-computed.

The test caused a segfault under a debug build without the fix applied.
This commit is contained in:
Fred Drake 2004-02-04 23:14:14 +00:00
parent 21ae4f983e
commit bc875f5a36
2 changed files with 48 additions and 3 deletions
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19
Objects/weakrefobject.c
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@ -630,16 +630,23 @@ PyWeakref_NewRef(PyObject *ob, PyObject *callback)
/* return existing weak reference if it exists */
result = ref;
if (result != NULL)
Py_XINCREF(result);
Py_INCREF(result);
else {
/* Note: new_weakref() can trigger cyclic GC, so the weakref
list on ob can be mutated. This means that the ref and
proxy pointers we got back earlier may have been collected,
so we need to compute these values again before we use
them. */
result = new_weakref(ob, callback);
if (result != NULL) {
if (callback == NULL) {
insert_head(result, list);
}
else {
PyWeakReference *prev = (proxy == NULL) ? ref : proxy;
PyWeakReference *prev;
get_basic_refs(*list, &ref, &proxy);
prev = (proxy == NULL) ? ref : proxy;
if (prev == NULL)
insert_head(result, list);
else
@ -672,8 +679,13 @@ PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
/* attempt to return an existing weak reference if it exists */
result = proxy;
if (result != NULL)
Py_XINCREF(result);
Py_INCREF(result);
else {
/* Note: new_weakref() can trigger cyclic GC, so the weakref
list on ob can be mutated. This means that the ref and
proxy pointers we got back earlier may have been collected,
so we need to compute these values again before we use
them. */
result = new_weakref(ob, callback);
if (result != NULL) {
PyWeakReference *prev;
@ -682,6 +694,7 @@ PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
result->ob_type = &_PyWeakref_CallableProxyType;
else
result->ob_type = &_PyWeakref_ProxyType;
get_basic_refs(*list, &ref, &proxy);
if (callback == NULL)
prev = ref;
else