Don't create a new list

Author: vstinner

Lib/asyncio/unix_events.py

@@ -1381,8 +1381,8 @@ def _join_threads(self, timeout=None):
             thread.join(timeout)
 
         # Clear references to terminated threads
-        self.threads = [thread for thread in list(self._threads.values())
-                        if thread.is_alive() and not thread.daemon]
+        self.threads[:] = [thread for thread in list(self._threads.values())
+                           if thread.is_alive() and not thread.daemon]
 
     def __enter__(self):
         return self