Paul Millar created ZOOKEEPER-2813:
--------------------------------------
Summary: Failure tight loop in acceptor
Key: ZOOKEEPER-2813
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2813
Project: ZooKeeper
Issue Type: Bug
Components: server
Affects Versions: 3.4.8
Reporter: Paul Millar
Priority: Minor
Fix For: 3.5.0
A failure during accepting an incoming connection results in the acceptor
thread being caught in a tight-loop. For example:
{noformat}
13 Jun 2017 15:31:39 (zookeeper) [] Ignoring unexpected runtime exception
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]
13 Jun 2017 15:31:39 (zookeeper) [] Ignoring unexpected runtime exception
java.lang.NullPointerException: null
at
org.apache.zookeeper.server.ZooKeeperServer.createSession(ZooKeeperServer.java:569)
~[zookeeper-3.4.8.jar:3.4.8--1]
at
org.apache.zookeeper.server.ZooKeeperServer.processConnectRequest(ZooKeeperServer.java:902)
~[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]
13 Jun 2017 15:31:40 (zookeeper) [] Ignoring unexpected runtime exception
java.lang.NullPointerException: null
at
org.apache.zookeeper.server.NIOServerCnxnFactory.run(NIOServerCnxnFactory.java:185)
~[zookeeper-3.4.8.jar:3.4.8--1]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]
13 Jun 2017 15:31:40 (zookeeper) [] Ignoring unexpected runtime exception
java.lang.NullPointerException: null
at
org.apache.zookeeper.server.NIOServerCnxnFactory.run(NIOServerCnxnFactory.java:185)
~[zookeeper-3.4.8.jar:3.4.8--1]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]
13 Jun 2017 15:31:40 (zookeeper) [] Ignoring unexpected runtime exception
java.lang.NullPointerException: null
at
org.apache.zookeeper.server.NIOServerCnxnFactory.run(NIOServerCnxnFactory.java:185)
~[zookeeper-3.4.8.jar:3.4.8--1]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]
{noformat}
The first stack-trace is due to ZOOKEEPER-2810, the second is due to
ZOOKEEPER-2812.
The other stack-traces (NPE from NIOServerCnxnFactory.java:185) are
never-ending, as the service has been caught in a tight-loop.
The reason is that the NIOServerCnxnFactory class fails to guarantee that
`selected` variable is clearer, so the SelectionKey that triggered the bugs
remains "live". However, since there are no incoming connections, the call to
`accept()` returns null, triggering the NPE.
It appears this problem is fixed with 3.5.0 (with commit 6302d7a7). If
back-porting this patch is too invasive, another solution might be to place the
`selected.clear()` statement inside the finally-clause of the try-statement.
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