rafactor, remove old todo, add some err msg.

lichao

2021-06-03 8967e7f2f8b94dc032135707e16c8a9f233d0db6

 src/exported_symbols

@@ -5,6 +5,7 @@
   BHUnregister;
   BHRegisterTopics;
   BHQueryTopicAddress;
   BHQueryProcs;
   BHSubscribeTopics;
   BHStartWorker;
   BHHeartbeatEasy;