Avoid 100% CPU usage while socket is closed

After stop/start kafka service, kafka-python may use 100% CPU caused by
busy-retry while the socket was closed. This fix the issue by adding a
0.1 second sleep if the fd is negative.

Author: orange-kao

kafka/client_async.py

@@ -634,6 +634,16 @@ def _poll(self, timeout):
             self._sensors.select_time.record((end_select - start_select) * 1000000000)
 
         for key, events in ready:
+            if key.fileobj.fileno() < 0:
+                # if there is no new message, self._selector.select() will take 0.1s.
+                # However, if the socket is closed, it could return immediately, result in
+                # high CPU usage because of busy-retry, caused by the loop in
+                #     producer/sender.py run()
+                #         calling producer/sender.py run_once()
+                #         calling lient_async.py poll()
+                #         calling lient_async.py _poll()
+                time.sleep(0.1)
+
             if key.fileobj is self._wake_r:
                 self._clear_wake_fd()
                 continue