ADDITIONAL SYSTEM INFORMATION :
Dell Precision Tower with :
- Intel(R) Xeon(R) CPU E5-1630 v4 @ 3.70GHz
- 32 Go RAM

Java: reproduced on all of these:
- 1.8.0_201-b09 HotSpot(TM) 64-Bit Server VM (build 25.201-b09, mixed mode)
- 1.8.0_172-b11
- openjdk-8-jdk 8u232-b09-0ubuntu1.1

OS:
  Distribution: Ubuntu 64 19.10
  C Library: GNU C Library / (Ubuntu GLIBC 2.30-0ubuntu2) 2.30
  Kernel : Linux 5.3.0-26-generic (x86_64)

A DESCRIPTION OF THE PROBLEM :
On Ubuntu 64 systems, EPollArrayWrapper.epollWait() may return events for removed file descriptors .

The consequences are that Jetty spins into infinite loops and consumes CPU core at 100% definitively for nothing. The only way to recover is to restart the application.

We make an Eclipse RCP application whose help system is based on a local embedded Jetty server. The help is displayed in a SWT Browser based on Webkit GTK widget.
Since SWT forced the usage of version 2 Webkit for the SWT Browser implementation we experience very often many CPU cores are at 100% indefinitively. Then only way to stop this is then to restart the application. This is a major inconvenience for our Linux users.

One week of debugging let me conclude that when the Jetty server closes an HTTP connection for being idle, it:
1) closes the connection,
2) removes the connection for the Selector
3) listen on the selector again
4) receive an event from the removed connection !!!

Here is a stacktrace where I paused the debugger, with some variables dumped:

Thread [qtp2141257835-54] (Suspended)
owns: EPollSelectorImpl (id=129)
owns: Collections$UnmodifiableSet<E> (id=130)
owns: Util$3 (id=131)
EPollArrayWrapper.poll(long) line: 270
EPollSelectorImpl.doSelect(long) line: 93
EPollSelectorImpl(SelectorImpl).lockAndDoSelect(long) line: 86
EPollSelectorImpl(SelectorImpl).select(long) line: 97
EPollSelectorImpl(SelectorImpl).select() line: 101
ManagedSelector$SelectorProducer.select() line: 466
ManagedSelector$SelectorProducer.produce() line: 403
EatWhatYouKill.produceTask() line: 357
EatWhatYouKill.doProduce(boolean) line: 181
EatWhatYouKill.tryProduce(boolean) line: 168
EatWhatYouKill.run() line: 126
ReservedThreadExecutor$ReservedThread.run() line: 366
QueuedThreadPool.runJob(Runnable) line: 765
QueuedThreadPool$2.run() line: 683
Thread.run() line: 748

this EPollArrayWrapper (id=429)
- epfd 128
- incomingInterruptFD 77
- outgoingInterruptFD 127
- registered BitSet (id=435) {184}
- updated 1
- updateDescriptors (id=436) [184, 0, 0, 0, ...
- eventsLow (id=433)
[150] -1
[184] 1

getDescriptor(0) returned 150

This bug might be the cause of the following forum posts:
- https://forum.flashphoner.com/threads/100-cpu-usage-from-netty-epoll.11390/
- https://www.eclipse.org/lists//jetty-users/msg07075.html
- https://stackoverflow.com/questions/25494752/high-cpu-utilization-for-threads-that-seem-to-be-waiting
- https://stackoverflow.com/questions/20475290/why-does-select-consume-so-much-cpu-time-in-my-program
- https://download.oracle.com/javaee-archive/grizzly.java.net/users/2015/09/6747.html
- https://github.com/eclipse/jetty.project/issues/1323
- http://jetty.4.x6.nabble.com/jetty-users-high-cpu-load-NIO-Jetty7-6-0-td4548266.html

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
I have a runnable jar file to reproduce the problem. It embeds a Jetty server, Eclipse SWT and code to reproduce the problem.

It is stored here : https://github.com/cedric780/EPollArrayWrapper-bug-demonstrator/blob/master/org.modelio.jre.epollarray.test-0.0.1-sources.jar

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The jar should consume few CPU time.
ACTUAL -
At least one CPU core is at 100% indefinitively.

---------- BEGIN SOURCE ----------
See here:
https://github.com/cedric780/EPollArrayWrapper-bug-demonstrator/blob/master/org.modelio.jre.epollarray.test-0.0.1-sources.jar

https://github.com/cedric780/EPollArrayWrapper-bug-demonstrator
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
I have written a java agent that patches EPollArrayWrapper .
It is in the same repository:
https://github.com/cedric780/EPollArrayWrapper-bug-demonstrator/blob/master/org.modelio.jre.epollarray.patch-0.0.1-sources.jar

FREQUENCY : often