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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