gh-117783: Immortalize objects that use deferred reference counting (#118112)

Deferred reference counting is not fully implemented yet. As a temporary
measure, we immortalize objects that would use deferred reference
counting to avoid multi-threaded scaling bottlenecks.

This is only performed in the free-threaded build once the first
non-main thread is started. Additionally, some tests, including refleak
tests, suppress this behavior.

1 files changed, 7 insertions, 0 deletions

diff --git a/Objects/object.c b/Objects/object.c
index 91bb011..8d85693 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -2430,6 +2430,13 @@ _PyObject_SetDeferredRefcount(PyObject *op)
     assert(PyType_IS_GC(Py_TYPE(op)));
     assert(_Py_IsOwnedByCurrentThread(op));
     assert(op->ob_ref_shared == 0);
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    if (interp->gc.immortalize.enabled) {
+        // gh-117696: immortalize objects instead of using deferred reference
+        // counting for now.
+        _Py_SetImmortal(op);
+        return;
+    }
     op->ob_gc_bits |= _PyGC_BITS_DEFERRED;
     op->ob_ref_local += 1;
     op->ob_ref_shared = _Py_REF_QUEUED;