Schedulers shutdown capability.

Proposal for shutting down the computation and io schedulers on demand.

#1730
This is not detailed in the requirements, but the implementation basically calls unsubscribe() and shutdownNow() which generally do best effort to terminate outstanding work. So it is quite possible an unresponsive/ignorant work may keep a worker thread operational and make Tomcat still print out the leak notification.

Is the underlying issue still relevant (almost a month passed with no feedback)?