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From Lars Engholm Johansen <lar...@gmail.com>
Subject Re: Connection count explosion due to thread http-nio-80-ClientPoller-x death
Date Mon, 10 Nov 2014 09:57:30 GMT
Hi Mark,

I looked into our javax.websocket.Endpoint implementation and found the
following suspicious code:

When we need to close the WebSocket session already in .onOpen() method
(rejecting a connection), we are calling session.close() asynchronously
after 1 second via a java.util.Timer task.
This was due to bug https://issues.apache.org/bugzilla/show_bug.cgi?id=54716,
that I can see should be fixed long time ago (thanks).

Can this cause the selector's keyset to be accessed by more than one thread?

Best regards,
Lars Engholm Johansen

On Mon, Oct 6, 2014 at 2:14 PM, Mark Thomas <markt@apache.org> wrote:

> On 06/10/2014 10:11, Lars Engholm Johansen wrote:
> > Hi all,
> >
> > I have good news as I have identified the reason for the devastating
> > NioEndpoint.Poller thread death:
> >
> > In rare circumstances a ConcurrentModification can occur in the Poller's
> > connection timeout handling called from OUTSIDE the try-catch(Throwable)
> of
> > Poller.run()
> >
> > java.util.ConcurrentModificationException
> >         at java.util.HashMap$HashIterator.nextEntry(HashMap.java:922)
> >         at java.util.HashMap$KeyIterator.next(HashMap.java:956)
> >         at
> >
> java.util.Collections$UnmodifiableCollection$1.next(Collections.java:1067)
> >         at
> >
> org.apache.tomcat.util.net.NioEndpoint$Poller.timeout(NioEndpoint.java:1437)
> >         at
> > org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:1143)
> >         at java.lang.Thread.run(Thread.java:745)
> >
> > Somehow the Poller's Selector object gets modified from another thread.
>
> Any idea how? I've been looking through that code for some time now
> (this stack trace appears to be from 7.0.55 for those that want to look
> at this themselves) and I can't see anywhere where the selector's keyset
> is accessed by more than one thread.
>
> > As a remedy until fixed properly by the Tomcat team, I have added a
> > try-catch(ConcurrentModificationException) surrounding the for loop in
> > Poller.timeout().
> > That way, in case of the rare problem, a full iteration of the Selector
> > will be retried in the next call to Poller.timeout().
>
> That seems like a reasonable work-around but before we start making
> changes to the Tomcat code I'd really like to understand the root
> cause(s) of the issue else we might not be fixing the actual issue and
> could make it worse for some folks.
>
> Mark
>
>
> >
> > I am really happy now as all our production servers have been rock stable
> > for two weeks now.
> >
> > Best regards to all,
> > Lars Engholm Johansen
> >
> >
> > On Thu, Sep 18, 2014 at 7:03 PM, Filip Hanik <filip@hanik.com> wrote:
> >
> >> Thanks Lars, if you are indeed experiencing a non caught error, let us
> know
> >> what it is.
> >>
> >> On Thu, Sep 18, 2014 at 2:30 AM, Lars Engholm Johansen <
> larsjo@gmail.com>
> >> wrote:
> >>
> >>> Thanks guys for all the feedback.
> >>>
> >>> I have tried the following suggested tasks:
> >>>
> >>>    - Upgrading Tomcat to the newest 7.0.55 on all our servers ->
> Problem
> >>>    still persists
> >>>    - Force a System.gc() when connection count is on the loose ->
> >>>    Connection count is not dropping
> >>>    - Lowering the log level of NioEndpoint class that contains the
> Poller
> >>>    code -> No info about why the poller thread exits in any tomcat logs
> >>>    - Reverting the JVM stack size per thread to the default is
> discussed
> >>>    previously -> Problem still persists
> >>>
> >>> I have now checked out the NioEndpoint source code and recompiled it
> >> with a
> >>> logging try-catch surrounding the whole of the Poller.run()
> >> implementation
> >>> as I noticed that the outer try-catch here only catches OOME.
> >>> I will report back with my findings as soon as the problem arises
> again.
> >>>
> >>> /Lars
> >>>
> >>>
> >>>
> >>> On Fri, Jun 27, 2014 at 9:02 PM, Christopher Schultz <
> >>> chris@christopherschultz.net> wrote:
> >>>
> > Filip,
> >
> > On 6/27/14, 11:36 AM, Filip Hanik wrote:
> >>>>>> Are there any log entries that would indicate that the poller
> >>>>>> thread has died? This/these thread/s start when Tomcat starts.
and
> >>>>>> a stack over flow on a processing thread should never affect
the
> >>>>>> poller thread.
> >
> > OP reported in the initial post that the thread had disappeared:
> >
> > On 6/16/14, 5:40 AM, Lars Engholm Johansen wrote:
> >>>>>> We have no output in tomcat or our logs at the time when this
event
> >>>>>>  occurs. The only sign is when comparing full java thread dump
with
> >>>>>> a dump from a newly launched Tomcat:
> >>>>>>
> >>>>>> One of  http-nio-80-ClientPoller-0  or  http-nio-80-ClientPoller-1
> >>>>>> is missing/has died.
> >
> > -chris
> >>>>
> >>>> ---------------------------------------------------------------------
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> >>>> For additional commands, e-mail: users-help@tomcat.apache.org
> >>>>
> >>>>
> >>>
> >>
> >
>
>
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>

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