Add support for applications which immediately exit

Sometimes an application doesn’t have any persistent services. Such applications should auto-exit after everything was “started”.

A good way to implement this might be for main-method startup build steps to indicate symbolically if they are persistent. Only a handful will be:

• Fixed thread pools like the scheduler
• I/O event loop threads

Notably, regular thread pools should not be considered persistent.

If no persistent services are started, then the shutdownRequested flag should be immediately set, which will cause the main thread to exit cleanly (with no exit code). The shutdown hook will then run, but as the application was already stopped, it will immediately exit with no action taken.

[geoand]

Being able to easily create Quarkus CLIs might be a good way of keeping people for using Go for such tools

[dmlloyd]

I’m almost finished with my current task, and this one will be next.