pythongh-128691: Use deferred reference counting on _thread._local (python#128693)

colesbury · web-flow · commit c1417487e98e · 2025-01-10T00:59:10.000Z
This change, along with the LOAD_ATTR specializations, makes the
"thread_local_read" micro benchmark in Tools/ftscalingbench/ftscalingbench.py
scale well to multiple threads.
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
@@ -1414,6 +1414,10 @@ local_new(PyTypeObject *type, PyObject *args, PyObject *kw)
         return NULL;
     }
 
+    // gh-128691: Use deferred reference counting for thread-locals to avoid
+    // contention on the shared object.
+    _PyObject_SetDeferredRefcount((PyObject *)self);
+
     self->args = Py_XNewRef(args);
     self->kw = Py_XNewRef(kw);
 

Original file line number	Diff line number	Diff line change
`@@ -1414,6 +1414,10 @@ local_new(PyTypeObject type, PyObject args, PyObject *kw)`
`1414`	`1414`	`return NULL;`
`1415`	`1415`	`}`
`1416`	`1416`
	`1417`	`+ // gh-128691: Use deferred reference counting for thread-locals to avoid`
	`1418`	`+ // contention on the shared object.`
	`1419`	`+ _PyObject_SetDeferredRefcount((PyObject *)self);`
	`1420`	`+`
`1417`	`1421`	`self->args = Py_XNewRef(args);`
`1418`	`1422`	`self->kw = Py_XNewRef(kw);`
`1419`	`1423`