Ensure asyncore dispatchers are closed on exit

CHANGELOG.rst

@@ -4,6 +4,7 @@
 Bug Fixes
 ---------
 * is_idempotent flag is not propagated from PreparedStatement to BoundStatement (PYTHON-736)
+* Fix asyncore hang on exit (PYTHON-767)
 
 3.10.0
 ======

cassandra/io/asyncorereactor.py

@@ -240,6 +240,8 @@ class AsyncoreLoop(object):
         self._timers.add_timer(timer)
 
     def _cleanup(self):
+        global _dispatcher_map
+
         self._shutdown = True
         if not self._thread:
             return
@@ -253,6 +255,12 @@ class AsyncoreLoop(object):
 
         log.debug("Event loop thread was joined")
 
+        # Ensure all connections are closed and  in-flight requests cancelled
+        for conn in tuple(_dispatcher_map.values()):
+            conn.close()
+
+        log.debug("Dispatchers were closed")
+
 
 class AsyncoreConnection(Connection, asyncore.dispatcher):
     """