tomcat集群 session复制的问题

tomcat7 + Apache 做集群，结果 session不能复制。
报这下面这个错，各位谁遇到这种情况？有解决思路？严重: Unable to perform replication request.
java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
        at java.util.HashMap$EntryIterator.next(HashMap.java:834)
        at java.util.HashMap$EntryIterator.next(HashMap.java:832)
        at java.util.HashMap.writeObject(HashMap.java:999)
        at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:94
0)
        at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:14
69)
        at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.jav
a:1400)
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1158)        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:330)
        at org.apache.catalina.ha.session.DeltaRequest$AttributeInfo.writeExtern
al(DeltaRequest.java:392)
        at org.apache.catalina.ha.session.DeltaRequest.writeExternal(DeltaReques
t.java:285)
        at org.apache.catalina.ha.session.DeltaRequest.serialize(DeltaRequest.ja
va:299)
        at org.apache.catalina.ha.session.DeltaManager.serializeDeltaRequest(Del
taManager.java:610)
        at org.apache.catalina.ha.session.DeltaManager.requestCompleted(DeltaMan
ager.java:996)
        at org.apache.catalina.ha.session.DeltaManager.requestCompleted(DeltaMan
ager.java:961)
        at org.apache.catalina.ha.tcp.ReplicationValve.send(ReplicationValve.jav
a:537)
        at org.apache.catalina.ha.tcp.ReplicationValve.sendMessage(ReplicationVa
lve.java:524)
        at org.apache.catalina.ha.tcp.ReplicationValve.sendSessionReplicationMes
sage(ReplicationValve.java:506)
        at org.apache.catalina.ha.tcp.ReplicationValve.sendReplicationMessage(Re
plicationValve.java:419)
        at org.apache.catalina.ha.tcp.ReplicationValve.invoke(ReplicationValve.j
ava:343)
        at org.apache.catalina.ha.session.JvmRouteBinderValve.invoke(JvmRouteBin
derValve.java:218)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.jav
a:408)
        at org.apache.coyote.ajp.AjpAprProcessor.process(AjpAprProcessor.java:19
0)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(
AbstractProtocol.java:607)
        at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpo
int.java:2442)
        at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoin
t.java:2431)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExec
utor.java:895)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor
.java:918)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskTh
read.java:61)
        at java.lang.Thread.run(Thread.java:662)
2017-9-26 10:53:33 org.apache.catalina.ha.tcp.ReplicationValve sendReplicationMe
ssage