weblogic.socket.Muxer uses 100% cpu

Question

We've recently started experiencing with deployments in Weblogic 12c using the `weblogic.Deployer` utility. We can deploy an EAR fine, but whenever we try to undeploy that application with the Managed Server still running it will start using 100% of our CPU (4-core Xeon, bare-metal). After some tinkering and countless thread dumps, we could isolate the problem on 4 stuck threads. Each one of them consumed 100% on a core. The load average would jump from something around 0.10 to 4.00 in 5 minutes tops. This is the threads that seems to be stuck: ``` "ExecuteThread: '3' for queue: 'weblogic.socket.Muxer'" daemon prio=10 tid=0x00007fb52801c800 nid=0x6bf0 runnable [0x00007fb58a0ad000] java.lang.Thread.State: RUNNABLE at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method) at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269) at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:79) at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:87) - locked <0x00000000e…

Accepted Answer

After much tinkering, an almost sleepless night and googling till I bled, I'm almost sure I got it solved.

This solution is heavily based on another thread: https://stackoverflow.com/a/7827952/1484232

To summarize the whole shebang, GC threads collision (most likely) were causing the issues here. After applying some parameters to my VM, it was magically solved.

```
-XX:+UseConcMarkSweepGC 
-XX:+UseParNewGC 
-XX:ParallelCMSThreads=2 
-XX:+CMSParallelRemarkEnabled 
-XX:+CMSIncrementalMode 
-XX:+CMSIncrementalPacing 
-XX:CMSFullGCsBeforeCompaction=1 
-XX:+CMSClassUnloadingEnabled 
-XX:CMSInitiatingOccupancyFraction=80
```

If anyone ever has the same trouble, this can be used as a try to get things working again.

Cheers.

weblogic.socket.Muxer uses 100% cpu

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