Use a copy of `self.contents` in this list comprehension.

Improved a fix first implemented for :ticket:`3208` released in version
0.9.8, where the registry of classes used internally by declarative could
be subject to a race condition in the case where individual mapped classes
are being garbage collected at the same time while new mapped classes are
being constructed, as can happen in some test suite configurations or
dynamic class creation environments.   In addition to the weakref check
already added, the list of items being iterated is also copied first to
avoid "list changed while iterating" errors.  Pull request courtesy Yilei
Yang.

Fixes: #10782
Closes: #10783
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/10783
Pull-request-sha: 354e97b640430120d0c193a4efe487f293d4768b

Change-Id: I04ccc92472bf1004dad0fb785e16b180f58f101d
(cherry picked from commit 0fe5d3ca51884b85b4059ed05b53f02172325e70)

diff --git a/doc/build/changelog/unreleased_14/10782.rst b/doc/build/changelog/unreleased_14/10782.rst
new file mode 100644 (file)
index 0000000..d7b219a
--- /dev/null
+++ b/doc/build/changelog/unreleased_14/10782.rst
@@ -0,0 +1,15 @@
+.. change::
+    :tags: bug, orm
+    :tickets: 10782
+    :versions: 2.0.24, 1.4.51
+
+    Improved a fix first implemented for :ticket:`3208` released in version
+    0.9.8, where the registry of classes used internally by declarative could
+    be subject to a race condition in the case where individual mapped classes
+    are being garbage collected at the same time while new mapped classes are
+    being constructed, as can happen in some test suite configurations or
+    dynamic class creation environments.   In addition to the weakref check
+    already added, the list of items being iterated is also copied first to
+    avoid "list changed while iterating" errors.  Pull request courtesy Yilei
+    Yang.
+

diff --git a/lib/sqlalchemy/orm/clsregistry.py b/lib/sqlalchemy/orm/clsregistry.py
index 4f4dab895e416a5f9e8f484cffb8867f0012240a..bb062c5c981cc4f6402710a5bf3d82e09a469582 100644 (file)
--- a/lib/sqlalchemy/orm/clsregistry.py
+++ b/lib/sqlalchemy/orm/clsregistry.py
@@ -239,10 +239,10 @@ class _MultipleClassMarker(ClsRegistryToken):
     def add_item(self, item: Type[Any]) -> None:
         # protect against class registration race condition against
         # asynchronous garbage collection calling _remove_item,
-        # [ticket:3208]
+        # [ticket:3208] and [ticket:10782]
         modules = {
             cls.__module__
-            for cls in [ref() for ref in self.contents]
+            for cls in [ref() for ref in list(self.contents)]
             if cls is not None
         }
         if item.__module__ in modules: