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From Thomas Vinod Johnson <Thomas.John...@Sun.COM>
Subject NullPointerException stopping and starting Zookeeper servers
Date Mon, 08 Dec 2008 19:33:24 GMT
Hi,
I have a replicated zookeeper services consisting of 3 zookeeper (3.0.1) 
servers all running on the same host for testing purposes. I've created 
exactly one znode in this ensemble. At this point, I stop, then restart 
a single zookeeper server; moving onto the next one a few seconds later. 
A few restarts later (about 4 is usually sufficient), I get the 
following exception on one of the servers, at which point it exits:
java.lang.NullPointerException
        at 
org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.next(FileTxnLog.java:447)
        at 
org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.init(FileTxnLog.java:358)
        at 
org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.<init>(FileTxnLog.java:333)
        at 
org.apache.zookeeper.server.persistence.FileTxnLog.read(FileTxnLog.java:250)
        at 
org.apache.zookeeper.server.persistence.FileTxnSnapLog.restore(FileTxnSnapLog.java:102)
        at 
org.apache.zookeeper.server.ZooKeeperServer.loadData(ZooKeeperServer.java:183)
        at org.apache.zookeeper.server.quorum.Leader.lead(Leader.java:245)
        at 
org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:421)
2008-12-08 14:14:24,880 - INFO  
[QuorumPeer:/0:0:0:0:0:0:0:0:2183:Leader@336] - Shutdown called
java.lang.Exception: shutdown Leader! reason: Forcing shutdown
        at 
org.apache.zookeeper.server.quorum.Leader.shutdown(Leader.java:336)
        at 
org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:427)
Exception in thread "QuorumPeer:/0:0:0:0:0:0:0:0:2183" 
java.lang.NullPointerException
        at 
org.apache.zookeeper.server.quorum.Leader.shutdown(Leader.java:339)
        at 
org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:427)

The inputStream field is null, apparently because next is being called 
at line 358 even after next returns false. Having very little knowledge 
about the implementation, I don't know if the existence of hdr.getZxid() 
 >= zxid is supposed to be an invariant across all invocations of the 
server; however the following change to FileTxnLog.java seems to make 
the problem go away.
diff FileTxnLog.java /tmp/FileTxnLog.java
358c358,359
<                 next();
---
 >               if (!next())
 >                   return;
447c448,450
<                 inputStream.close();
---
 >               if (inputStream != null) {
 >                   inputStream.close();
 >               }

Is this a bug?

Thanks.


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