From aefbe1e3038a6871a8da94a966d084b06373d096 Mon Sep 17 00:00:00 2001
From: Dino Viehland <dinoviehland@fb.com>
Date: Fri, 26 Jul 2024 14:32:19 -0700
Subject: [PATCH 1/2] Don't delivery PyDict_EVENT_ADDED until it can't fail

---
 Objects/dictobject.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 254cd9ad2f9bda..a99f32a9c84c95 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -1251,10 +1251,6 @@ 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. */
@@ -1262,6 +1258,11 @@ insertdict(PyInterpreterState *interp, PyDictObject *mp,
                 goto Fail;
         }
 
+        uint64_t new_version = _PyDict_NotifyEvent(
+                interp, PyDict_EVENT_ADDED, mp, key, value);
+        /* Insert into new slot. */
+        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);
 
@@ -1335,9 +1336,6 @@ 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);
     PyDictKeysObject *newkeys = new_keys_object(
             interp, PyDict_LOG_MINSIZE, unicode);
@@ -1346,6 +1344,9 @@ 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;
@@ -3324,15 +3325,15 @@ 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)) {

From edd939e372e501d5daafdfa6455bf7854f2f73cb Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Fri, 26 Jul 2024 21:38:51 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../2024-07-26-21-38-47.gh-issue-122208.z8KHsY.rst               | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2024-07-26-21-38-47.gh-issue-122208.z8KHsY.rst

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-07-26-21-38-47.gh-issue-122208.z8KHsY.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-07-26-21-38-47.gh-issue-122208.z8KHsY.rst
new file mode 100644
index 00000000000000..e4a89d137ede0e
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-07-26-21-38-47.gh-issue-122208.z8KHsY.rst
@@ -0,0 +1 @@
+Dictionary watchers now only deliver the PyDict_EVENT_ADDED event when the insertion is in a known good state to succeed.