Dear,

I got a problem when querying. The weird problem is that the error happens on Unix box but not on a window box.



15:28:54,103 ERROR [[AjaxMethodOfInstructionByCourseRequirementServlet]] Servlet.service() for servlet AjaxMethodOfInstructionByCourseRequirementServlet threw exception
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
at java.util.HashMap$ValueIterator.next(Unknown Source)
at org.hibernate.pretty.Printer.toString(Printer.java:113)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:120)
at org.hibernate.event.def.DefaultAutoFlushEventListener.onAutoFlush(DefaultAutoFlushEventListener.java:58)
at org.hibernate.impl.SessionImpl.autoFlushIfRequired(SessionImpl.java:996)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1141)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
at com.cmaps.core.persist.dao.InstructionalMethodDao.getUniversalList(InstructionalMethodDao.java:35)
at com.cmaps.servlet.AjaxMethodOfInstructionByCourseRequirementServlet.doAjax(AjaxMethodOfInstructionByCourseRequirementServlet.java:40)
at com.cmaps.servlet.AjaxServlet.doGet(AjaxServlet.java:23)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:829)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:601)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)
15:29:16,210 INFO [STDOUT] 443449 [Timer-1] INFO com.mchange.v2.resourcepool.BasicResourcePool - A checked-out resource is overdue, and will be destroyed: com.mchange.v2.c3p0.impl.NewPooledConnection@27f07e81

Which version of hibernate do you use?

Answer: hibernate3.jar

Sometimes, when I do query.list(), I got the same problem (ConcurrentModificationException)
It only happens on unix box, not on window os.

Looks like you are having more threads running concurrently operating on the same hiberante session.
This would mean a incorrect use of Hibernate.
While the thread relative to your stacktrace was iterating a hashmap for read-only purpose (toString method),
another thread modified that hashmap causing the exception you report here.

Some year ago I had the same problem, when there sometimes were longterm blocking resources on database (locks) while flushing.
This caused a long client-server-roundtrip and after a couple of time (timeout) our proxy did resend the same request again.
This caused in tomcat the start of a second worker-tread acting on the same hibernate session as the other one which still waited the end of flushing. After the lock on database dissappeared, there were race-conditionsbetween the two threads (= 2 threads doing the same in non-thread safe code) causing exceptions like the one you reported.