[jira] [Created] (ZOOKEEPER-4296) NullPointerException when ClientCnxnSocketNetty is closed without being opened

["Colvin Cowie (Jira)" <ji...@apache.org>]

Colvin Cowie created ZOOKEEPER-4296:
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             Summary: NullPointerException when ClientCnxnSocketNetty is closed without being opened
                 Key: ZOOKEEPER-4296
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4296
             Project: ZooKeeper
          Issue Type: Bug
    Affects Versions: 3.6.2, 3.6.3, 3.5.3, 3.5.9
            Reporter: Colvin Cowie


I believe this bug was originally reported as ZOOKEEPER-2966 but that was closed as not reproducible in February 2019. I left a comment with these details on that issue in December. I can create a PR with a fix at some point this week.

 

In ZooKeeper 3.6.2, in the context of the SolrJ client, we hit the NPE reported on ZOOKEEPER-2966 when a DNS error causes an exception after the SolrZkClient trys to connect to ZooKeeper, but then immediately calls close on the {{ClientCnxn}} [https://github.com/apache/lucene-solr/blob/master/solr/solrj/src/java/org/apache/solr/common/cloud/SolrZkClient.java#L158-L204].
{noformat}
java.lang.NullPointerException: null
        at org.apache.zookeeper.ClientCnxnSocketNetty.onClosing(ClientCnxnSocketNetty.java:247) ~[zookeeper-3.6.2.jar:3.6.2]
        at org.apache.zookeeper.ClientCnxn$SendThread.close(ClientCnxn.java:1445) ~[zookeeper-3.6.2.jar:3.6.2]
        at org.apache.zookeeper.ClientCnxn.disconnect(ClientCnxn.java:1488) ~[zookeeper-3.6.2.jar:3.6.2]
        at org.apache.zookeeper.ClientCnxn.close(ClientCnxn.java:1517) ~[zookeeper-3.6.2.jar:3.6.2]
        at org.apache.zookeeper.ZooKeeper.close(ZooKeeper.java:1614) ~[zookeeper-3.6.2.jar:3.6.2]
        at org.apache.solr.common.cloud.SolrZooKeeper.close(SolrZooKeeper.java:97) ~[solr-solrj-8.7.0.jar:8.7.0 2dc63e901c60cda27ef3b744bc554f1481b3b067 - atrisharma - 2020-10-29 19:39:18]
        at org.apache.solr.common.cloud.SolrZkClient.<init>(SolrZkClient.java:198) ~[solr-solrj-8.7.0.jar:8.7.0 2dc63e901c60cda27ef3b744bc554f1481b3b067 - atrisharma - 2020-10-29 19:39:18]
        at org.apache.solr.common.cloud.SolrZkClient.<init>(SolrZkClient.java:127) ~[solr-solrj-8.7.0.jar:8.7.0 2dc63e901c60cda27ef3b744bc554f1481b3b067 - atrisharma - 2020-10-29 19:39:18]
        at org.apache.solr.common.cloud.SolrZkClient.<init>(SolrZkClient.java:122) ~[solr-solrj-8.7.0.jar:8.7.0 2dc63e901c60cda27ef3b744bc554f1481b3b067 - atrisharma - 2020-10-29 19:39:18]
        at org.apache.solr.common.cloud.SolrZkClient.<init>(SolrZkClient.java:109) ~[solr-solrj-8.7.0.jar:8.7.0 2dc63e901c60cda27ef3b744bc554f1481b3b067 - atrisharma - 2020-10-29 19:39:18]
{noformat}
This happens if the {{ClientCnxnSocketNetty}}'s {{onClosing()}} is called before {{connect(...)}} (or if connect isn't called at all) because the {{firstConnect}} {{CountDownLatch}} is only initialized in {{connect(...)}}.
 [https://github.com/apache/zookeeper/blob/master/zookeeper-server/src/main/java/org/apache/zookeeper/ClientCnxnSocketNetty.java#L129]
 [https://github.com/apache/zookeeper/blob/master/zookeeper-server/src/main/java/org/apache/zookeeper/ClientCnxnSocketNetty.java#L247]
 A null check in {{onClosing()}} will fix it, but I don't know if there's any greater change required, e.g. some synchronization around connect and onClosing.

The code in [3.5.3|https://github.com/apache/zookeeper/blame/1507f67a06175155003722297daeb60bc912af1d/zookeeper-server/src/main/java/org/apache/zookeeper/ClientCnxnSocketNetty.java#L206] looks very similar.



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