The threads in the thread pool used for Proc.joinWithTimeout inherit their context class loader from the thread that calls Proc.joinWithTimeout, which seems undesirable. While looking into JENKINS-50223, I found a case where one of the threads in the thread pool was holding onto a CleanGroovyClassLoader class loader from workflow-cps (see the attached screenshot), which is definitely undesirable.

We should wrap this thread pool in ClassLoaderSanityThreadFactory to prevent this kind of issue from happening.