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https://issues.apache.org/jira/browse/ZOOKEEPER-2383?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15502832#comment-15502832
 ] 

Flavio Junqueira commented on ZOOKEEPER-2383:
---------------------------------------------

Actually, what prevents us from doing this:

{noformat}
--- a/src/java/main/org/apache/zookeeper/server/NIOServerCnxnFactory.java
+++ b/src/java/main/org/apache/zookeeper/server/NIOServerCnxnFactory.java
@@ -113,10 +113,10 @@ public void start() {
     @Override
     public void startup(ZooKeeperServer zks) throws IOException,
             InterruptedException {
-        start();
         setZooKeeperServer(zks);
         zks.startdata();
         zks.startup();
+        start();
     }
{noformat}

Interestingly, the tests pass for me with this change, so if it doesn't work, 
then we have at least a test coverage problem.

> Startup race in ZooKeeperServer
> -------------------------------
>
>                 Key: ZOOKEEPER-2383
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2383
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: jmx, server
>    Affects Versions: 3.4.8
>            Reporter: Steve Rowe
>            Assignee: Rakesh R
>            Priority: Blocker
>             Fix For: 3.4.10, 3.5.3, 3.6.0
>
>         Attachments: TestZkStandaloneJMXRegistrationRaceConcurrent.java, 
> ZOOKEEPER-2383-br-3-4.patch, ZOOKEEPER-2383.patch, ZOOKEEPER-2383.patch, 
> ZOOKEEPER-2383.patch, release-3.4.8-extra-logging.patch, 
> zk-3.4.8-MBeanRegistry.log, zk-3.4.8-NPE.log
>
>
> In attempting to upgrade Solr's ZooKeeper dependency from 3.4.6 to 3.4.8 
> (SOLR-8724) I ran into test failures where attempts to create a node in a 
> newly started standalone ZooKeeperServer were failing because of an assertion 
> in MBeanRegistry.
> ZooKeeperServer.startup() first sets up its request processor chain then 
> registers itself in JMX, but if a connection comes in before the server's JMX 
> registration happens, registration of the connection will fail because it 
> trips the assertion that (effectively) its parent (the server) has already 
> registered itself.
> {code:java|title=ZooKeeperServer.java}
>     public synchronized void startup() {
>         if (sessionTracker == null) {
>             createSessionTracker();
>         }
>         startSessionTracker();
>         setupRequestProcessors();
>         registerJMX();
>         state = State.RUNNING;
>         notifyAll();
>     }
> {code}
> {code:java|title=MBeanRegistry.java}
>     public void register(ZKMBeanInfo bean, ZKMBeanInfo parent)
>         throws JMException
>     {
>         assert bean != null;
>         String path = null;
>         if (parent != null) {
>             path = mapBean2Path.get(parent);
>             assert path != null;
>         }
> {code}
> This problem appears to be new with ZK 3.4.8 - AFAIK Solr never had this 
> issue with ZK 3.4.6. 



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