[jira] [Commented] (HELIX-264) fix zkclient#close() bug

["Hudson (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HELIX-264?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13786503#comment-13786503 ] 

Hudson commented on HELIX-264:
------------------------------

FAILURE: Integrated in helix #1188 (See [https://builds.apache.org/job/helix/1188/])
[HELIX-264] fix zkclient#close() bug, rb=14483 (zzhang: rev b9fe738797cd5228e8ecaa284c8874bfa19f1ff2)
* helix-core/src/test/java/org/apache/helix/manager/zk/TestZkFlapping.java
* helix-core/src/test/java/org/apache/helix/ZkTestHelper.java
* helix-core/src/main/java/org/apache/helix/manager/zk/ZkClient.java


> fix zkclient#close() bug
> ------------------------
>
>                 Key: HELIX-264
>                 URL: https://issues.apache.org/jira/browse/HELIX-264
>             Project: Apache Helix
>          Issue Type: Bug
>            Reporter: Zhen Zhang
>            Assignee: Zhen Zhang
>            Priority: Critical
>
> When the flapping is detected, we are in the zkclient event thread context and we are calling zkclient.close() from its own event thread. Here is the ZkClient#close():
>     public void close() throws ZkInterruptedException {
>         if (_connection == null) {
>             return;
>         }
>         LOG.debug("Closing ZkClient...");
>         getEventLock().lock();
>         try {
>             setShutdownTrigger(true);
>             _eventThread.interrupt();
>             _eventThread.join(2000);
>             _connection.close();
>             _connection = null;
>         } catch (InterruptedException e) {
>             throw new ZkInterruptedException(e);
>         } finally {
>             getEventLock().unlock();
>         }
>         LOG.debug("Closing ZkClient...done");
>     }
> _eventThread.interrupt(); <-- will set interrupt status of _eventThread which is in fact the currentThread.
> _eventThread.join(2000); <-- will throw InterruptedException because currentThread has been interrupted.
> _connection.close(); <-- SKIPPED!!!
> So if flapping happens, we are calling ZkHelixManager#disconnectInternal(), which will always interrupt ZkClient#_eventThread but never disconnect the zk connection. This is probably a zkclient bug that we should never call zkclient.close() from its own event thread context.
> fix steps:
> 1) workaround for this bug
> 2) add test cases for flapping detection
> 3) explore the possibility to have controller detect flapping participants and disable them (may via querying zk-server jmx metrics)



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