Deadlock found when send 'GET_NOTE' OP message

org.apache.zeppelin.socket.ConnectionManager#addNoteConnection   deadlock at 

'synchronized (noteSocketMap)'

Zeppelin occasionally fails to respond when click paragraph or refresh notebook page, but other functions such as login and configuration are normal. 
 
This phenomenon has appeared for the third time, and you must to restart it to restore service.

Test it by remote debug and jstack log found that deadlock occur when addNoteConnection method, see more jstack log in attachments please.

Note: I used the remote debugging on this instance some time ago. I am not sure weather it caused by one of the debugging connections disconnect then cause incompletable request.