gh-128008: Add `PyWeakref_IsDead()` (GH-128009)

The `PyWeakref_IsDead()` function tests if a weak reference is dead
without any side effects. Although you can also detect if a weak
reference is dead using `PyWeakref_GetRef()`, that function returns a
strong reference that must be `Py_DECREF()`'d, which can introduce side
effects if the last reference is concurrently dropped (at least in the
free threading build).

1 files changed, 13 insertions, 0 deletions

diff --git a/Objects/weakrefobject.c b/Objects/weakrefobject.c
index 9e3da1c..0ee64ed 100644
--- a/Objects/weakrefobject.c
+++ b/Objects/weakrefobject.c
@@ -932,6 +932,19 @@ PyWeakref_NewProxy(PyObject *ob, PyObject *callback)
     return (PyObject *)get_or_create_weakref(type, ob, callback);
 }
 
+int
+PyWeakref_IsDead(PyObject *ref)
+{
+    if (ref == NULL) {
+        PyErr_BadInternalCall();
+        return -1;
+    }
+    if (!PyWeakref_Check(ref)) {
+        PyErr_Format(PyExc_TypeError, "expected a weakref, got %T", ref);
+        return -1;
+    }
+    return _PyWeakref_IS_DEAD(ref);
+}
 
 int
 PyWeakref_GetRef(PyObject *ref, PyObject **pobj)