From b45420da66e86d0bcc9c9614faeff70a02ebf0b5 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Wed, 6 May 2020 17:14:47 +0200
Subject: [PATCH] bpo-40533: Make PyObject.ob_refcnt atomic in subinterpreters

When Python is built with experimental isolated interpreters, declare
PyObject.ob_refcnt and _dictkeysobject.dk_refcnt as atomic variables.

Temporary workaround until subinterpreters stop sharing Python
objects.
---
 Include/object.h      | 7 +++++++
 Objects/dict-common.h | 6 ++++++
 2 files changed, 13 insertions(+)

diff --git a/Include/object.h b/Include/object.h
index 6c30809124dea8..123e967ad6053b 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -104,7 +104,14 @@ typedef struct _typeobject PyTypeObject;
  */
 typedef struct _object {
     _PyObject_HEAD_EXTRA
+#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
+    /* bpo-40533: Use an atomic variable for PyObject.ob_refcnt, to ensure that
+       Py_INCREF() and Py_DECREF() are safe when called in parallel, until
+       subinterpreters stop sharing Python objects. */
+    _Atomic Py_ssize_t ob_refcnt;
+#else
     Py_ssize_t ob_refcnt;
+#endif
     PyTypeObject *ob_type;
 } PyObject;
 
diff --git a/Objects/dict-common.h b/Objects/dict-common.h
index 71d6b0274420b8..3383cd90248d2c 100644
--- a/Objects/dict-common.h
+++ b/Objects/dict-common.h
@@ -20,7 +20,13 @@ typedef Py_ssize_t (*dict_lookup_func)
 
 /* See dictobject.c for actual layout of DictKeysObject */
 struct _dictkeysobject {
+#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
+    /* bpo-40533: Use an atomic variables until subinterpreters stop sharing
+       Python dictionaries. */
+    _Atomic Py_ssize_t dk_refcnt;
+#else
     Py_ssize_t dk_refcnt;
+#endif
 
     /* Size of the hash table (dk_indices). It must be a power of 2. */
     Py_ssize_t dk_size;