https://getakka.net/articles/actors/coordinated-shutdown.html

Can we just use the "Coordinated Shutdown" for safely shutting down the NeoSystem?

Looks like it is available in the core parts of Akka. I'll work on switching this to use CoordinatedShutdown.

@erikzhang The solution is clean now and uses CoordinatedShutdown

Sounds good to me, Jeff.
Just wonder if it is possible to test this following that strategy used for the Consensus, but here starting everything and closing unexpectedly.

but here starting everything and closing unexpectedly.

@vncoelho It's working fine from my testing, can you give more details about the error you are getting?

I did not get errors, I did not have time to check yet. I was mentioning about the possibility of a Unit Test.

I was mentioning about the possibility of a Unit Test.

Well, there is certainly the possibility, and it would be nice to improve unit test coverage for the Blockchain class in general. For now I think it is relying a lot on manual integration testing. I suppose a unit test for the behavior of ShutdownAndWaitForIdle shouldn't be too difficult to add at some point, though not sure I will add it right now.

I've done manual integration testing of these changes with neo-cli.

That is it, maybe following this template:

We can create and initialize the actors and, then, kill/stop it.
I can try to do it in a couple of days.

@erikzhang I made changes to the PR so it no longer waits for the Blockchain to be idle. Now it just ensures the actors are stopped in the right order. It adds two CoordinatedShutdown phases the user can add tasks to in order to delay shutdown according to their needs. Akka doesn't seem to provide any way to tell when the Actor is stopped, except it provides the PostStop lifecycle hook in the actor, so I had to expose methods that use a semaphore to be able to wait asynchronously until the actor is stopped.

Should be good now, just needs a bit of testing.

I think stopping an actor and waiting for it to complete can be done with GracefulStop().

https://getakka.net/articles/actors/receive-actor-api.html#graceful-stop

GracefulStop is useful if you need to wait for termination or compose ordered termination of several actors.

@erikzhang that would require it processing all the messages in the queue to get to the message that stops it gracefully, which you said you didn't want to do earlier. If we want to throw the current messages in the actor queues away, then that doesn't work for us.