gh-129069: use atomic _PyList_GetItemRef in stringlib_bytes_join

part of TSAN-0013 in gh-153852

Author: xxyzz

Objects/bytearrayobject.c

@@ -9,6 +9,7 @@
 #include "pycore_object.h"        // _PyObject_GC_UNTRACK()
 #include "pycore_strhex.h"        // _Py_strhex_with_sep()
 #include "pycore_long.h"          // _PyLong_FromUnsignedChar()
+#include "pycore_list.h"          // _PyList_GetItemRef
 #include "pycore_pyatomic_ft_wrappers.h"
 #include "bytesobject.h"
 

Objects/stringlib/join.h

@@ -60,7 +60,16 @@ STRINGLIB(bytes_join)(PyObject *sep, PyObject *iterable)
      */
     for (i = 0, nbufs = 0; i < seqlen; i++) {
         Py_ssize_t itemlen;
+#ifdef Py_GIL_DISABLED
+        if (PyList_Check(seq)) {
+            item = _PyList_GetItemRef((PyListObject *)seq, i);
+        }
+        else {
+            item = PyTuple_GET_ITEM(seq, i);
+        }
+#else
         item = PySequence_Fast_GET_ITEM(seq, i);
+#endif
         if (PyBytes_CheckExact(item)) {
             /* Fast path. */
             buffers[i].obj = Py_NewRef(item);