Hi, Thanks for working on issue ZEPPELIN-1856. I think removing 'note.clearParagraphOutput(paragraphId);' from 'onOutputClear()' is not the best solution, because without the line 'onOutputClear()' does not do anything useful.
InterpreterContext is constructed before call RemoteInterpreterServer.interpret(). So OUTPUT_UPDATE_ALL supposed to arrive before RemoteInterpreterServer.interpret() returns. Apparently, it looks like it doesn't. So i think we need to tackle this problem. OUTPUT_UPDATE_ALL event is delivered via RemoteInterpreterEventClient/RemoteInterpreterEventPoller, while RemoteInterpreterServer.interpret() does not, and RemoteInterpreterEventClient/RemoteInterpreterEventPoller does not guarantee message deliver before interpret() returns. That's origin of problem i think. Therefore, proper way solving this problem is add some mechanism that guarantee RemoteInterpreterEventClient/RemoteInterpreterEventPoller deliver the OUTPUT_UPDATE_ALL event before interpret() returns. Or simple workaround could be ignore OUTPUT_UPDATE_ALL event when paragraph becomes FINISHED status (after interpret() returns). Thanks, moon On Sat, Feb 4, 2017 at 12:02 AM Alexander Shoshin < alexander_shos...@epam.com> wrote: > Hi, > > I'm working on issue https://issues.apache.org/jira/browse/ZEPPELIN-1856 > and I found that we receive a NullPointerException sometimes because a > paragraph result is cleared twice when we run a job. First Paragraph.result > is cleared just before running RemoteInterpreter.interpret(..) and this is > ok. But then we receive an OUTPUT_UPDATE_ALL event from the > RemoteInterpreterServer and set Paragraph.result to null again that may > lead to a NullPointerException if Paragraph.result was already filled by > RemoteInterpreter.interpret(..) responce. > > To resolve this problem we need to remove > note.clearParagraphOutput(paragraphId) line from the onOutputClear() method > in NotebookServer.java class: > > @Override > public void onOutputClear(String noteId, String paragraphId) { > Notebook notebook = notebook(); > final Note note = notebook.getNote(noteId); > note.clearParagraphOutput(paragraphId); // this line seems to be > wrong > Paragraph paragraph = note.getParagraph(paragraphId); > broadcastParagraph(note, paragraph); > } > > This method is called only when RemoteInterpreterServer.interpret(..) > initializes an InterpreterContext and sends an OUTPUT_UPDATE_ALL event. > Is it safe to remove this line or I miss something? It was added by > https://github.com/apache/zeppelin/pull/1658. > > Thanks, > Alexander >
