Defensive copy for BoundedList deque iter

Author: c24t

opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py

@@ -59,7 +59,8 @@ def __len__(self):
         return len(self._dq)
 
     def __iter__(self):
-        return iter(self._dq)
+        with self._lock:
+            return iter(self._dq.copy())
 
     def append(self, item):
         with self._lock: