Implement PyUnstable_Object_SetDeferredRefcount

Author: Peter Bierma

Include/cpython/object.h

@@ -526,3 +526,5 @@ typedef enum {
 typedef int (*PyRefTracer)(PyObject *, PyRefTracerEvent event, void *);
 PyAPI_FUNC(int) PyRefTracer_SetTracer(PyRefTracer tracer, void *data);
 PyAPI_FUNC(PyRefTracer) PyRefTracer_GetTracer(void**);
+
+PyAPI_FUNC(int) PyUnstable_Object_SetDeferredRefcount(PyObject *);

Objects/object.c

@@ -2482,6 +2482,37 @@ _PyObject_SetDeferredRefcount(PyObject *op)
 #endif
 }
 
+int
+PyUnstable_Object_SetDeferredRefcount(PyObject *op)
+{
+#ifdef Py_GIL_DISABLED
+    if (!PyType_IS_GC(Py_TYPE(op)))
+    {
+        PyErr_SetString(PyExc_TypeError,
+                     "object is not tracked by the garbage collector");
+        return -1;
+    }
+
+    if (!_Py_IsOwnedByCurrentThread(op))
+    {
+        PyErr_SetString(PyExc_ValueError,
+                        "object is not owned by this thread");
+        return -1;
+    }
+
+    if (op->ob_ref_shared != 0)
+    {
+        PyErr_SetString(PyExc_ValueError,
+                        "object is already in use by another thread");
+        return -1;
+    }
+
+    _PyObject_SET_GC_BITS(op, _PyGC_BITS_DEFERRED);
+    op->ob_ref_shared = _Py_REF_SHARED(_Py_REF_DEFERRED, 0);
+#endif
+    return 0;
+}
+
 void
 _Py_ResurrectReference(PyObject *op)
 {