restore the check ahead of the lock to avoid using it after initialization

is done

1 files changed, 7 insertions, 6 deletions

diff --git a/lib/sqlalchemy/event/attr.py b/lib/sqlalchemy/event/attr.py
index ca94493f5..a3a0d48dc 100644
--- a/lib/sqlalchemy/event/attr.py
+++ b/lib/sqlalchemy/event/attr.py
@@ -240,12 +240,13 @@ class _CompoundListener(_HasParentDispatchDescriptor):
         """Execute this event, but only if it has not been
         executed already for this collection."""
 
-        with self._exec_once_mutex:
-            if not self._exec_once:
-                try:
-                    self(*args, **kw)
-                finally:
-                    self._exec_once = True
+        if not self._exec_once:
+            with self._exec_once_mutex:
+                if not self._exec_once:
+                    try:
+                        self(*args, **kw)
+                    finally:
+                        self._exec_once = True
 
     def __call__(self, *args, **kw):
         """Execute this event."""