[MC-143854] Idle java server load 100% on snapshots

Starting a fresh minecraft server running it with:

/opt/jdk1.8.0_202/bin/java -d64 -Xmx4g -jar server.jar

/opt/jdk-11.0.2/bin/java -Xmx4g -jar server.jar

...where server.jar is one of the following versions:

18w43a
19w04a
19w05a
19w06a

...yields in a server starting up, generating and loading the world and then waiting for somebody to connect. One of the CPU cores remains on 100% at all times, even after quite some runtime, when somebody is connected or nobody is connected anymore. I had a server running over night and it was still on 100% cpu usage.

I've tested the same scenario with v1.13.2 server.jar and after the initial generation and loading phase, the cpu usage drops first to like 16% and then below 3% and remains there.

I am able to run jvisualvm, if necessary. Since I have not much experience with the tool (and which probings you would need), I could supply you with the necessary data.

However if you'd just test this setup, you should get the same result and analyse this yourself.

Please fix for the next snapshot!