The Jenkins Gearman plugin has originally be written for OpenStack (now OpenDev), they have phased out Jenkins from their architecture and the plugin has been unmaintained since. However, I have found out another company forked it and addressed a few issues with it, most notably Java 11. We should thus use their repository, rebuild our plugin and upgrade.
The rough topology of the git repositories:
|https://github.com/jenkinsci/gearman-plugin||Dummy one just having a README|
|https://opendev.org/x/gearman-plugin||Original canonical repository, the version WMF runs|
The Gearman plugin depends on gearman-java which does not work under Java 11 due to a breaking change https://www.oracle.com/java/technologies/javase/jdk-11-relnote.html#JDK-8200458