[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3006) ConcurrentModificationException in AbstractBatcher results in infinite loop

[Steve Ebersole (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_29503 ] 

Steve Ebersole commented on HHH-3006:
-------------------------------------

The attached test case uses a separate thread to achieve this concurrent modification problem.  In "real life" this would mean you would have to have 2 (or more) threads simultaneously accessing the same session.  That is explicitly disallowed.  

Can you reproduce this error w/o resorting to separate threads?

If this is something which happens simply because there is actually a concurrent modification scenario with multiple threads accessing the same collection, then there is nothing to fix (aside from the the code which accesses the same session from multiple concurrent threads).

> ConcurrentModificationException in AbstractBatcher results in infinite loop
> ---------------------------------------------------------------------------
>
>                 Key: HHH-3006
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3006
>             Project: Hibernate3
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 3.2.5
>         Environment: Hibernate 3.2.5.ga
> MySQL 5.0.42
>            Reporter: Stefan Hauk
>            Priority: Minor
>         Attachments: batcherinfinitelooptest.zip, batcherinfinitelooptest.zip
>
>
> Here is a piece of code from org.hibernate.jdbc.AbstractBatcher's closeStatements() method:
> Iterator iter = resultSetsToClose.iterator();
> while ( iter.hasNext() ) {
> 	try {
> 		logCloseResults();
> 		( (ResultSet) iter.next() ).close();
> 	}
> 	catch (SQLException e) {
> 		// no big deal
> 		log.warn("Could not close a JDBC result set", e);
> 	}
> 	catch (Throwable e) {
> 		// sybase driver (jConnect) throwing NPE here in certain cases
> 		log.warn("Could not close a JDBC result set", e);
> 	}
> }
> resultSetsToClose.clear();
> In case there is a ConcurrentModificationException thrown when iterating over the resultSetsToClose HashSet the exception will be caught by the catch(Throwable) clause. However, the iteration may continue infinitely because of the corrupted HashSet. This pegs one CPU and logs the following stack trace over and over again:
> 28/11 20:16:50 WARN AbstractBatcher [resin-tcp-connection-myserver:6001-15] Could not close a JDBC result set
> java.util.ConcurrentModificationException
> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:841)
> at java.util.HashMap$KeyIterator.next(HashMap.java:877)
> at org.hibernate.jdbc.AbstractBatcher.closeStatements(AbstractBatcher.java:314)
> at org.hibernate.jdbc.ConnectionManager.cleanup(ConnectionManager.java:382)
> at org.hibernate.jdbc.ConnectionManager.close(ConnectionManager.java:324)
> at org.hibernate.impl.SessionImpl.close(SessionImpl.java:298)
> at org.springframework.orm.hibernate3.SessionFactoryUtils.closeSession(SessionFactoryUtils.java:774)
> at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.closeSession(OpenSessionInViewFilter.java:252)
> at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:183)
> at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:75)
> at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:70)
> at com.caucho.server.cache.CacheFilterChain.doFilter(CacheFilterChain.java:188)
> at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:178)
> at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:229)
> at com.caucho.server.hmux.HmuxRequest.handleRequest(HmuxRequest.java:419)
> at com.caucho.server.port.TcpConnection.run(TcpConnection.java:389)
> at com.caucho.util.ThreadPool.runTasks(ThreadPool.java:492)
> at com.caucho.util.ThreadPool.run(ThreadPool.java:425)
> at java.lang.Thread.run(Thread.java:595)
> The catch(Throwable) block was added in Hibernate 3.2.3 if I saw that correctly. Apparently the reason was to catch a NPE thrown by a sybase driver here, but catching Throwable catches more than that and produces this side-effect.
> Now I do realize that the ConcurrentModificationException might be caused by not using Hibernate in a correct way, but I haven't determined the cause for it yet. However, I do think that Hibernate should fail more gracefully than it currently does.

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