Due to some complexity in mojangs complicated chain of juggling
whether or not a chunk should be unloaded when the last ticket is
removed, many chunks are remaining around in the cache.
These chunks are never being targetted for unload because they are
vastly out of view distance range and have no reason to be looked at.
This is a huge issue for performance because we have to iterate these
chunks EVERY TICK... This is what's been leading to high SELF time in
Ticking Chunks timings/profiler results.
We will now detect these chunks in that iteration, and automatically
add it to the unload queue when the chunk is found without any tickets.
This is for 2 reasons:
1) Ensuring our log4j is mostly loaded at OUR version.
I've seen stack traces with line numbers that do not match our version. This means that some
plugin has shaded in log4j and their loaded version is mixing with ours....
So by at least trying to load a bunch of log4j classes before we load plugins, we can be
more sure mixed versions are not loading.
2) If the jar file is replaced while the server is runnimg class not found errors galore
This will preloaod a bunch of classes commonly seen to error during shutdown due to this.
The goal here is to help let the server shutdown gracefully as possible. Some plugins will
still blow up here if they access a class that hadn't been loaded yet, but goal is to at least
stop freezing the shutdown process as it does with JLine and Log4j errors requiring an external kill.
Ideally you should not replace jars while the server is running, but it is something that happens in
development for testing.
Updated test server to do a copy though to avoid this happening in Paper development.
Blow up if a plugin tries to mutate visibleChunks directly and prevent them
from doing so.
Also provide a safe get call if any plugins directly call get on it so
that it uses the special logic to check pending.
Also restores ABI for the visibleChunks field back to what it was too.
Additionally, remove the stack trace from Timings Stack Corruption for any
error thrown on Minecraft Timings, and tell them to get the error ABOVE this
instead, so people stop giving us useless error reports.
Also fixes a memory leak when the source map down sizes but dest map didn't,
which resulted in lingering references to old chunk holders.
Fixes#3414
Mark chunks that are blocking main thread for world generation as urgent
Implements a general priority system so that chunks that are sorted in
the generator queues can prioritize certain chunks over another.
Urgent chunks will jump to the front of the line, ensuring that a
sync chunk load on an ungenerated chunk does not lag the server for
a long period of time if the servers generator queues are filled with
lots of chunks already.
This massively reduces the lag spikes from sync chunk gens.
Then we further prioritize loading order so nearby chunks have higher
priority than distant chunks, reducing the pressure a high no tick
view distance holds on you.
Chunks in front of the player have higher priority, to help with
fast traveling players keep up with their movement.
This commit also improves single core cpu scenarios in that we will
now automatically disable Async Chunks as well as Minecrafts thread
pool.
It is never recommended to use async chunks on a single CPU as context
switching will be slower than just running it all on main.
This also bumps the number of server worker threads by default too.
Mojang does not utilize the workers in an effecient manner, resulting
in them using barely any sustained CPU.
So give it more workers so more chunks can be processed concurrently
This change also improves urgent chunk loading, so players flying into
unloaded chunks will hurt a little bit less (but still hurt)
Ping #3395#3363 (Not marking as closed, we need to make prevent moving work)
