gh-112529: Make the GC scheduling thread-safe (#114880)

The GC keeps track of the number of allocations (less deallocations)
since the last GC. This buffers the count in thread-local state and uses
atomic operations to modify the per-interpreter count. The thread-local
buffering avoids contention on shared state.

A consequence is that the GC scheduling is not as precise, so
"test_sneaky_frame_object" is skipped because it requires that the GC be
run exactly after allocating a frame object.

1 files changed, 2 insertions, 0 deletions

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 0118ee2..2e25c20 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -1835,6 +1835,8 @@ _PyType_AllocNoTrack(PyTypeObject *type, Py_ssize_t nitems)
     if (presize) {
         ((PyObject **)alloc)[0] = NULL;
         ((PyObject **)alloc)[1] = NULL;
+    }
+    if (PyType_IS_GC(type)) {
         _PyObject_GC_Link(obj);
     }
     memset(obj, '\0', size);