From 4fc0bc34226dc548360d3ce724af0829d40adbc0 Mon Sep 17 00:00:00 2001
From: Dino Viehland <dinoviehland@meta.com>
Date: Wed, 24 Jul 2024 16:35:14 -0700
Subject: [PATCH] Deliver dict added event only after it's guaranteed to
 succeed

Summary:
Back port of: https://github.com/python/cpython/pull/122207 fixing https://github.com/python/cpython/issues/122208

The current dictionary watchers implementation delivers the added event before it checks to see if we need to re-size the dictionary. This resize can fail so the value isn't added, and then the tracker is out of sync with the true state of the dictionary.

This moves the delivery of the event to after any necessary allocations have happened.

Reviewed By: jbower-fb

Differential Revision: D60182094

fbshipit-source-id: f34940e98ce1caadeee364f9d126d35839661961
---
 Objects/dictobject.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index b0aefca918a..8126bef5ec6 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -1390,10 +1390,7 @@ insertdict(PyInterpreterState *interp, PyDictObject *mp,
     MAINTAIN_TRACKING(mp, key, value);
 
     if (ix == DKIX_EMPTY) {
-        uint64_t new_version = _PyDict_NotifyEvent(
-                interp, PyDict_EVENT_ADDED, mp, key, value);
         /* Insert into new slot. */
-        mp->ma_keys->dk_version = 0;
         assert(old_value == NULL);
         if (mp->ma_keys->dk_usable <= 0) {
             /* Need to resize. */
@@ -1401,6 +1398,10 @@ insertdict(PyInterpreterState *interp, PyDictObject *mp,
                 goto Fail;
         }
 
+        uint64_t new_version = _PyDict_NotifyEvent(
+                interp, PyDict_EVENT_ADDED, mp, key, value);
+        mp->ma_keys->dk_version = 0;
+
         Py_ssize_t hashpos = find_empty_slot(mp->ma_keys, hash);
         dictkeys_set_index(mp->ma_keys, hashpos, mp->ma_keys->dk_nentries);
 
@@ -1482,9 +1483,6 @@ insert_to_emptydict(PyInterpreterState *interp, PyDictObject *mp,
 {
     assert(mp->ma_keys == Py_EMPTY_KEYS);
 
-    uint64_t new_version = _PyDict_NotifyEvent(
-            interp, PyDict_EVENT_ADDED, mp, key, value);
-
     int unicode = PyUnicode_CheckExact(key);
     int lazy_imports = PyLazyImport_CheckExact(value);
     PyDictKeysObject *newkeys = new_keys_object(
@@ -1494,6 +1492,9 @@ insert_to_emptydict(PyInterpreterState *interp, PyDictObject *mp,
         Py_DECREF(value);
         return -1;
     }
+    uint64_t new_version = _PyDict_NotifyEvent(
+            interp, PyDict_EVENT_ADDED, mp, key, value);
+
     /* We don't decref Py_EMPTY_KEYS here because it is immortal. */
     mp->ma_keys = newkeys;
     mp->ma_values = NULL;
@@ -3671,15 +3672,15 @@ PyDict_SetDefault(PyObject *d, PyObject *key, PyObject *defaultobj)
         return NULL;
 
     if (ix == DKIX_EMPTY) {
-        uint64_t new_version = _PyDict_NotifyEvent(
-                interp, PyDict_EVENT_ADDED, mp, key, defaultobj);
-        mp->ma_keys->dk_version = 0;
         value = defaultobj;
         if (mp->ma_keys->dk_usable <= 0) {
             if (insertion_resize(interp, mp, 1) < 0) {
                 return NULL;
             }
         }
+        uint64_t new_version = _PyDict_NotifyEvent(
+                interp, PyDict_EVENT_ADDED, mp, key, defaultobj);
+        mp->ma_keys->dk_version = 0;
         Py_ssize_t hashpos = find_empty_slot(mp->ma_keys, hash);
         dictkeys_set_index(mp->ma_keys, hashpos, mp->ma_keys->dk_nentries);
         if (DK_IS_UNICODE(mp->ma_keys)) {