CB used the dirty flag to construct the chunk unload event,
but then sets mustNotSave to the inverted value of the event
after calling the event without considering that the chunk may
actually be brought up to loaded status again later. Then, CB
overrides the isUnsaved method of LevelChunk to additionally
use mustNotSave.
Thus, if the chunk is not marked dirty when unloading, the
mustNotSave value will be set to true. Then, once the chunk
is reloaded and edited the dirty flag will be set. However,
when unloading the chunk finally, the isUnsaved method
will return false due to mustNotSave being true. Thus, the
chunk will never be saved.
To fix these issues, no longer make mustNotSave override
isUnsaved and always set the save flag for the chunk unload
event.
This issue started popping up recently due to the recent
change to mark chunks as not dirty after saving them, which
increased the chance of the save issue occurring in the first
place.
When we update the chunk state to border, it should be
the case that isChunkLoaded returns true and that
getChunkIfLoadedImmediately returns a non-null value.
Now add the chunk to the loaded map before making any
callbacks after updating to border state.
Previously, PoiChunk#empty would create a new empty poi chunk with
loaded already set to true, as no data was contained in the chunk.
This allowed the poi chunk to skip expensive trips to the main thread.
However, PoiChunk#parse used #empty to create the initial PoiChunk
instance that is then filled with data.
This leads to PoiChunks returned from #parse to already be marked as
loaded, preventing the then needed trip to the tick thread to update
things like the village distance tracker.
To fix this, this commit now marks the PoiChunks loaded state as false
if the parse logic actually read and parsed any data.
This allows the PoiChunk#load method to properly run its callbacks when
called for the first time.
Patch documentation to come
Issues with the old system that are fixed now:
- World generation does not scale with cpu cores effectively.
- Relies on the main thread for scheduling and maintaining chunk state, dropping chunk load/generate rates at lower tps.
- Unreliable prioritisation of chunk gen/load calls that block the main thread.
- Shutdown logic is utterly unreliable, as it has to wait for all chunks to unload - is it guaranteed that the chunk system is in a state on shutdown that it can reliably do this? Watchdog shutdown also typically failed due to thread checks, which is now resolved.
- Saving of data is not unified (i.e can save chunk data without saving entity data, poses problems for desync if shutdown is really abnormal.
- Entities are not loaded with chunks. This caused quite a bit of headache for Chunk#getEntities API, but now the new chunk system loads entities with chunks so that they are ready whenever the chunk loads in. Effectively brings the behavior back to 1.16 era, but still storing entities in their own separate regionfiles.
The above list is not complete. The patch documentation will complete it.
New chunk system hard relies on starlight and dataconverter, and most importantly the new concurrent utilities in ConcurrentUtil.
Some of the old async chunk i/o interface (i.e the old file io thread reroutes _some_ calls to the new file io thread) is kept for plugin compat reasons. It will be removed in the next major version of minecraft.
The old legacy chunk system patches have been moved to the removed folder in case we need them again.
