If the request to shut down the server is received while we are in
a watchdog hang, immediately treat it as a crash and begin the shutdown
process. Shutdown process is now improved to also shutdown cleanly when
not using restart scripts either.
If a server is deadlocked, a server owner can send SIGHUP (or any other signal
the JVM understands to shut down as it currently does) and the watchdog
will no longer need to wait until the full timeout, allowing you to trigger
a close process and try to shut the server down gracefully, saving player and
world data.
Previously there was no way to trigger this outside of waiting for a full watchdog
timeout, which may be set to a really long time...
Additionally, fix everything to do with shutting the server down asynchronously.
Previously, nearly everything about the process was fragile and unsafe. Main might
not have actually been frozen, and might still be manipulating state.
Or, some reuest might ask main to do something in the shutdown but main is dead.
Or worse, other things might start closing down items such as the Console or Thread Pool
before we are fully shutdown.
This change tries to resolve all of these issues by moving everything into the stop
method and guaranteeing only one thread is stopping the server.
We then issue Thread Death to the main thread of another thread initiates the stop process.
We have to ensure Thread Death propagates correctly though to stop main completely.
This is to ensure that if main isn't truely stuck, it's not manipulating state we are trying to save.
Very few entities actually hard collide, so store them in their own
entity slices and provide a special getEntites type call just for them.
This reduces entity collision checking impact (in my testing) by 25%
for crammed entities (shove 130 cows into an 8x6 area in one chunk).
Less crammed entities are likely to show significantly less benefit.
Effectively, this patch optimises crammed entity situations.
