Jenkins currently has two ways of restarting the controller: Restart now (currently running jobs are killed) and Safe Restart (Wait for all jobs to complete or pause but do not accept any new jobs).

We have very long-running jobs (Machine Learning) that cannot pause for sometimes 30-60 minutes. If we trigger a safe restart in that time, the queue is blocked for that whole time and everyone is waiting for a single job to enter a pausable state.

A solution that would solve this issue is a new restart option, that simply waits until no builds are running without disabling the queue. The downside is obviously that the jenkins admin would like to immediately know if the startup works and don't want to monitor their screen for 3 hours until a slot is found. For this, a notification could be sent via mail, notification, ... ("Jenkins restarts in 60 seconds").

There are alternative solutions but I wanted to put it out here for discussion.