Hi Emmanuel, Thanks for your helpful response and the link to the original JDK ticket. I guess it was closed without being truly fixed!
Re-registering the channel on the new selector is exactly what NioProcessor.registerNewSelector() looks to be doing. Looking at this code in the mina sources again while reading your response, I noticed that this method is taking securing selectorLock.writeLock().lock() before it creates and registers the new selector (and releasing it at the end). NioProcessor.setInterestedInWrite(…) though is not getting the lock before it called key.interestOps(newInterestOps) which is where the ClosedSelectorException occurs. Is this failure to get the lock here the issue? Thanks, Adam From: Emmanuel Lecharny <[email protected]> Sent: 23 September 2025 13:29 To: Herring, Adam <[email protected]>; [email protected] Subject: Re: Possible second race condition after EPoll spinning causing ClosedSelectorException Hi Adam, comments inline. . . On 9/23/25 10: 46, Herring, Adam wrote: > Hi Apache MINA team, > > I'm seeking advice on how to handle an apparent race condition encountered using mina 2. 0. 27, whether my analysis is correct and if this is ZjQcmQRYFpfptBannerStart This Message Is From an Unknown Sender You have not previously corresponded with this sender. Use caution when clicking links or opening attachments. Report suspicious emails by clicking the "Report" button in your Outlook toolbar or forward to [email protected]<mailto:[email protected]>. ZjQcmQRYFpfptBannerEnd Hi Adam, comments inline... On 9/23/25 10:46, Herring, Adam wrote: > Hi Apache MINA team, > > I'm seeking advice on how to handle an apparent race condition encountered > using mina 2.0.27, whether my analysis is correct and if this is a known > issue (I haven't identified one open in > https://urldefense.com/v3/__https://issues.apache.org/jira/projects/DIRMINA/issues/DIRMINA-1186?filter=allopenissues__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBdYz_3sI$<https://urldefense.com/v3/__https:/issues.apache.org/jira/projects/DIRMINA/issues/DIRMINA-1186?filter=allopenissues__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBdYz_3sI$>). > > Issue Description > > Our application server uses MINA for NIO between a data cache and several > client applications. Recently we have seen increased incidence of the > following warning-level message in the data cache logs: > > Create a new selector. Selected is 0, delta = 0 > > I found this is logged from the AbstractPollingIoProcessor and is accompanied > by a comment block explaining that there is an Epoll race condition that can > cause file descriptors not to be considered available and the selector must > be closed and a new one registered to prevent 100% CPU use. It's not entirely > clear whether this issue is in MINA, the JDK or the operating system, but > either way this all seems fine and most of our application instances do not > encounter a further problem. It's a JDK problem, I do'nt think it was ever fixed: https://urldefense.com/v3/__https://bugs.openjdk.org/browse/JDK-8011538__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBXBjAtn4$<https://urldefense.com/v3/__https:/bugs.openjdk.org/browse/JDK-8011538__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBXBjAtn4$> > > On one production instance of our application it looks like a second race > condition occurs when the selector is closed and replaced. The greater the > frequency of the "Create a new selector. Selected is 0, delta = 0" message, > the more likely that we encounter a ClosedSelectorException on another > thread. Full stack trace and logs before and after: > > WARN 2025-09-10 21:58:29,212 [NioProcessor-2]-service.IoProcessor: Create a > new selector. Selected is 0, delta = 0 > WARN 2025-09-10 21:58:29,220 [pool-3-thread-2]-server.DsrvServerIoHandler: > null > java.nio.channels.ClosedSelectorException: null > at > sun.nio.ch.EPollSelectorImpl.ensureOpen(EPollSelectorImpl.java:98) ~[?:?] > at > sun.nio.ch.EPollSelectorImpl.setEventOps(EPollSelectorImpl.java:243) ~[?:?] > at > sun.nio.ch.SelectionKeyImpl.interestOps(SelectionKeyImpl.java:101) ~[?:?] > at > org.apache.mina.transport.socket.nio.NioProcessor.setInterestedInWrite(NioProcessor.java:371) > ~[mina-core-2.0.27.jar:?] > at > org.apache.mina.transport.socket.nio.NioProcessor.setInterestedInWrite(NioProcessor.java:47) > ~[mina-core-2.0.27.jar:?] > at > org.apache.mina.core.polling.AbstractPollingIoProcessor.updateTrafficControl(AbstractPollingIoProcessor.java:585) > [mina-core-2.0.27.jar:?] > at > org.apache.mina.core.polling.AbstractPollingIoProcessor.updateTrafficControl(AbstractPollingIoProcessor.java:68) > [mina-core-2.0.27.jar:?] > at > org.apache.mina.core.service.SimpleIoProcessorPool.updateTrafficControl(SimpleIoProcessorPool.java:294) > [mina-core-2.0.27.jar:?] > at > org.apache.mina.core.service.SimpleIoProcessorPool.updateTrafficControl(SimpleIoProcessorPool.java:80) > [mina-core-2.0.27.jar:?] > at > org.apache.mina.core.session.AbstractIoSession.resumeRead(AbstractIoSession.java:748) > [mina-core-2.0.27.jar:?] > at > j4sf.connect.dsrv.endpoint.IoSessionEndPoint.resumeRead(IoSessionEndPoint.java:73) > [DataServer-11.0.2.jar:?] > at > j4sf.connect.dsrv.server.SerialExecutor.scheduleNext(SerialExecutor.java:94) > [DataServer-11.0.2.jar:?] > at > j4sf.connect.dsrv.server.SerialExecutor$LocalTask.run(SerialExecutor.java:140) > [DataServer-11.0.2.jar:?] > at > java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) > [?:?] > at > java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) > [?:?] > at java.lang.Thread.run(Thread.java:829) [?:?] > INFO 2025-09-10 21:58:29,235 [NioProcessor-2]-server.DsrvServerIoHandler: > Session Closed > > Our code in the j4sf.connect.dsrv.server.SerialExecutor and > j4sf.connect.dsrv.endpoint.IoSessionEndpoint is handling reading incoming > messages on the IoSession. There is a message processing queues with a high > and low watermark. At some point we have exceeded the high watermark and > called suspendRead() on the IoSession. The ClosedConnectorException above has > thrown when we called ioSession.resumeRead(). > > Our DsrvServerIoHandler extends org.apache.mina.core.service.IoHandlerAdapter > - the exception is caught here where we override > IoHandlerAdapter.exceptionCaught(IoSession, Throwable). At this point we log > the exception and close the session, resulting in the final log message above > after the session has closed. > > We've been unable to reproduce this on a hardware/software platform under our > control. > > I don't see any mention of ClosedSelectorException in your mail archive since > handling of them was fixed in > DIRMINA-978<https://urldefense.com/v3/__https://issues.apache.org/jira/browse/DIRMINA-978__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBMS-GwrI$<https://urldefense.com/v3/__https:/issues.apache.org/jira/browse/DIRMINA-978__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBMS-GwrI$>> > > Questions: > > > 1. Could this be a race condition with the resumeRead causing the > NioProcessor retrieving the old selection key just before it was closed, then > attempting the read after it has been closed? Yes, because the thread that deals with the selector replacement is different from the thread processing the messages. > > > 1. The IoSession is already suspended when this happens - is there any > reason inherent in MINA why we shouldn't ignore this exception, at least > once, and simply attempt to resumeRead() again. If I could reproduce the > issue outside prod, I would of course try this myself. > If not, do you have any other advice on how the issue might be worked around. I *think* (but this is from the top of my head) that the necessary step to fix the issue is re-register the channel on the new selector, but it has to be present. So as soon as the previous identified race condition is fixed, this issue should bot occur. It would probably be enough to add a lock section where we span a new selector that blocks any operation on the selector. May be an AtomicReference to the selector itself could help? > > > > 1. Might upgrade to MINA 2.1 or 2.2 help? I see nothing obvious I the > release notes that suggests it would. We have already upgraded from 2.0.21 to > 2.0.27 which seems to have reduced the frequency of the issue - perhaps due > to the inclusion on > DIRMINA-1169<https://urldefense.com/v3/__https://issues.apache.org/jira/browse/DIRMINA-1169__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBw0EGOts$<https://urldefense.com/v3/__https:/issues.apache.org/jira/browse/DIRMINA-1169__;!!Ebr-cpPeAnfNniQ8HSAI-g_K5b7VKg!NbCVM_Tb4VZ_vqj39z3rMyVYgqSJttqNJGeI3p-J0iuMY3V7NzTMKrPAO5XcNB--SxJXHWIzsX5x2UMBw0EGOts$>> > in 2.0.24. No, I'm afraid that won't help. Although I encourage you to migrate, 2.0.X is pretty old... (6 years since 2.1 has been release) > > > > 1. Finally, do you know anything about likely causes of the initial Epoll > race condition the MINA code is working around. If it's caused by java, is > there an OpenJDK issue open related to it? I couldn't find anything that seem > to match. FWIW the system the issue occurs on is running RHEL 9.5 and the JDK > is also Red Hat's java 11: Red_Hat-11.0.17.0.8-2.el7openjdkportable As I mentionned above, JDK bug. MINA is not the only NIO framework handling a spinning selector this way :/ > > > Thanks! > Adam > > This message and any attachments are intended only for the use of the > addressee and may contain information that is privileged and confidential. If > the reader of the message is not the intended recipient or an authorized > representative of the intended recipient, you are hereby notified that any > dissemination of this communication is strictly prohibited. If you have > received this communication in error, please notify us immediately by e-mail > and delete the message and any attachments from your system. > --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected]<mailto:[email protected]> For additional commands, e-mail: [email protected]<mailto:[email protected]> This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system.
