Make shutdown cause/trigger available

[xtaixe]

Description

CLI apps might need to know if shutdown is due to normal exit or due to Ctrl+C/SIGINT, so there should be a way to distinguish those (and maybe other signals too).

Implementation ideas

Enhance the ShutdownEvent with some kind of "cause" or "trigger" property or maybe have different events to observe for different shutdown triggers.

[quarkus-bot]

/cc @manovotn, @mkouba

[manovotn]

That's not a bad idea, we could add some information into the event, but I have no clue when it comes to determining the cause of shutdown. Looking at Quarkus code, we have StartupContext and ShutdownContext but that doesn't seem very helpful as those are just auto closeables.

@geoand any idea how/if we could achieve that?

[geoand]

It's actually pretty easy in Quarkus code to determine whether or not the shutdown came from a SIGINT as io.quarkus.runtime.ApplicationLifecycleManager$ShutdownHookThread is the Shutdown Hook involved.

Ultimately io.quarkus.runtime.StartupContext#close gets called (no matter what the source of the shutdown is) so if we have some state in there we could propagate it

[manovotn]

CLI apps might need to know if shutdown is due to normal exit or due to Ctrl+C/SIGINT, so there should be a way to distinguish those (and maybe other signals too).

@xtaixe What exactly do you consider a "normal" exit for CLI app? I.e how do you quit the app in a normal way?
Also what other signals do you think are worth distinguishing? I don't see much value in telling user if it was SIGINT or SIGTERM but i might be missing something.

It's actually pretty easy in Quarkus code to determine whether or not the shutdown came from a SIGINT as io.quarkus.runtime.ApplicationLifecycleManager$ShutdownHookThread is the Shutdown Hook involved.

@geoand I saw ShutdownHookThread but that's simply invoked on every shutdown and I don't see a way to determine why shutdown happened from the thread itself.
I noticed we also have SignalHandler that can do exactly this but those seem to only be registered in native image and without certain system env set. There is probably a good reason for that too,

[geoand]

I saw ShutdownHookThread but that's simply invoked on every shutdown and I don't see a way to determine why shutdown happened from the thread itself

It's only invoked when the shutdown comes from a SIGINT, not from a normal program termination or application code initiated termination.

[xtaixe]

@manovotn

What exactly do you consider a "normal" exit for CLI app?

Maybe I didn't express that properly. I meant the program just finishes cause there's nothing more to do (e.g. ls) as opposed to keep running doing or waiting for something (e.g. tail/follow logs), which in our case is when you need to stop it using CTRL+C.

Also what other signals do you think are worth distinguishing? I don't see much value in telling user if it was SIGINT or SIGTERM but i might be missing something.

Maybe it's not worth distinguishing. In our case it's not needed, as long we can distinguish finishing from interrupted is enough. But if the information is already there maybe just provide it and let the user decide.

[manovotn]

Right, we can only probably differentiate between normal program finish and "all else".
That is, a situation when ShutdownHookThread is not invoked (normal) and when it is invoked (SIGINT, SIGTERM, ... but also System.exit()).

I'll try to get to it later this week and put together a PR.