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From: bugzilla@apache.org
To: dev@tomcat.apache.org
Subject: [Bug 54086] New: ConcurrentModificationException in NioReceiver on
 shutdown
Date: Thu, 01 Nov 2012 13:32:28 +0000
Message-ID: <bug-54086-78@https.issues.apache.org/bugzilla/>
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https://issues.apache.org/bugzilla/show_bug.cgi?id=3D54086

          Priority: P2
            Bug ID: 54086
          Assignee: dev@tomcat.apache.org
           Summary: ConcurrentModificationException in NioReceiver on
                    shutdown
          Severity: normal
    Classification: Unclassified
                OS: Solaris
          Reporter: clucas@e-miles.com
          Hardware: Sun
            Status: NEW
           Version: 7.0.30
         Component: Cluster
           Product: Tomcat 7

Solaris 10 x86, jdk 1.7.

We use tomcat clustering for session replication with 4 nodes and sometimes=
 8
nodes.  We get a ConcurrentModificationException occasionally on shutdown. =
 I
have been unable to reliably reproduce the exception. In the log, I see "Un=
able
to close cluster receiver selector." with the exception below:

java.util.ConcurrentModificationException=20
    java.util.HashMap$HashIterator.nextEntry(HashMap.java:894)=20
    java.util.HashMap$KeyIterator.next(HashMap.java:928)=20
    java.util.Collections$UnmodifiableCollection$1.next(Collections.java:10=
67)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Btransport.=
=E2=80=8Bnio.=E2=80=8BNioReceiver.=E2=80=8BcloseSelector(=E2=80=8BNioReceiv=
er.=E2=80=8Bjava:382)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Btransport.=
=E2=80=8Bnio.=E2=80=8BNioReceiver.=E2=80=8BstopListening(=E2=80=8BNioReceiv=
er.=E2=80=8Bjava:365)=20
=20=20=20
org.apache.catalina.tribes.transport.nio.NioReceiver.stop(NioReceiver.java:=
86)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8BChannelCoordinator.=E2=80=8BinternalStop(=E2=80=8BChannelCoordinator.jav=
a:203)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8BChannelCoordinator.=E2=80=8Bstop(=E2=80=8BChannelCoordinator.=E2=80=8Bja=
va:115)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8BChannelInterceptorBase.=E2=80=8Bstop(=E2=80=8BChannelInterceptorBase.jav=
a:178)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8BChannelInterceptorBase.=E2=80=8Bstop(=E2=80=8BChannelInterceptorBase.jav=
a:178)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8BChannelInterceptorBase.=E2=80=8Bstop(=E2=80=8BChannelInterceptorBase.jav=
a:178)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8Binterceptors.=E2=80=8BMessageDispatchInterceptor.=E2=80=8Bstop(=E2=80=8B=
MessageDispatchInterceptor.java:172)
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8BChannelInterceptorBase.=E2=80=8Bstop(=E2=80=8BChannelInterceptorBase.jav=
a:178)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Btribes.=E2=80=8Bgroup.=E2=80=
=8BChannelInterceptorBase.=E2=80=8Bstop(=E2=80=8BChannelInterceptorBase.jav=
a:178)=20
    org.apache.catalina.tribes.group.GroupChannel.stop(GroupChannel.java:43=
8)=20
=20=20=20
org.=E2=80=8Bapache.=E2=80=8Bcatalina.=E2=80=8Bha.=E2=80=8Btcp.=E2=80=8BSim=
pleTcpCluster.=E2=80=8BstopInternal(=E2=80=8BSimpleTcpCluster.=E2=80=8Bjava=
:=E2=80=8B744)=20
    org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)=20
=20=20=20
org.apache.catalina.core.ContainerBase.stopInternal(ContainerBase.java:1199=
)=20
    org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)=20
=20=20=20
org.apache.catalina.core.StandardService.stopInternal(StandardService.java:=
502)=20
    org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)=20
=20=20=20
org.apache.catalina.core.StandardServer.stopInternal(StandardServer.java:75=
3)=20
    org.apache.catalina.util.LifecycleBase.stop(LifecycleBase.java:232)=20
    org.apache.catalina.startup.Catalina.stop(Catalina.java:751)=20
    org.apache.catalina.startup.Catalina.start(Catalina.java:713)=20
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)=20
=20=20=20
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:5=
7)=20
=20=20=20
sun.=E2=80=8Breflect.=E2=80=8BDelegatingMethodAccessorImpl.=E2=80=8Binvoke(=
=E2=80=8BDelegatingMethodAccessorImpl.=E2=80=8Bjava:43)=20
    java.lang.reflect.Method.invoke(Method.java:601)=20
    org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:322)=20
    org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:451)

I looked at the code briefly and noticed the use of a SelectionKey Iterator=
.  I
have not dug deep enough to find any issue in the NioReceiver code, but I d=
id
find this potentially relevant text in the Selector javadocs
(http://docs.oracle.com/javase/7/docs/api/java/nio/channels/Selector.html):

"A selector's key and selected-key sets are not, in general, safe for use by
multiple concurrent threads. If such a thread might modify one of these sets
directly then access should be controlled by synchronizing on the set itsel=
f.
The iterators returned by these sets' iterator methods are fail-fast: If the
set is modified after the iterator is created, in any way except by invoking
the iterator's own remove method, then a ConcurrentModificationException wi=
ll
be thrown."

--=20
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