Paul Millar created ZOOKEEPER-2810:
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Summary: Racy implicit ZKDatabase creation
Key: ZOOKEEPER-2810
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2810
Project: ZooKeeper
Issue Type: Bug
Components: server
Affects Versions: 3.4.8
Reporter: Paul Millar
Priority: Minor
The NIOServerCnxnFactory#startup method first starts the acceptor thread and
then initialises the ZooKeeperServer instance. In particular, the call to
ZooKeeperServer#startdata method creates the ZKDatabase if it does not already
exist.
This creates a race-condition: if the acceptor thread accepts an incoming
connection before the ZKDatabase is established then there is a
NullPointerException:
{noformat}
java.lang.NullPointerException: null
at
org.apache.zookeeper.server.ZooKeeperServer.processConnectRequest(ZooKeeperServer.java:864)
~[zookeeper-3.4.8.jar:3.4.8--1]
at
org.apache.zookeeper.server.NIOServerCnxn.readConnectRequest(NIOServerCnxn.java:418)
~[zookeeper-3.4.8.jar:3.4.8--1]
at
org.apache.zookeeper.server.NIOServerCnxn.readPayload(NIOServerCnxn.java:198)
~[zookeeper-3.4.8.jar:3.4.8--1]
at
org.apache.zookeeper.server.NIOServerCnxn.doIO(NIOServerCnxn.java:244)
~[zookeeper-3.4.8.jar:3.4.8--1]
at
org.apache.zookeeper.server.NIOServerCnxnFactory.run(NIOServerCnxnFactory.java:203)
~[zookeeper-3.4.8.jar:3.4.8--1]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]
{noformat}
The same problem appears to be present in release-3.5 and master branches.
The naive fix would be to start the acceptor thread last in
NIOServerCnxnFactory#startup, but I can't say whether this would cause any
other problems.
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