Upstream has released updates that appears to apply and compile correctly.
This update has not been tested by PaperMC and as with ANY update, please do your own testing
CraftBukkit Changes:
eb2e6578 SPIGOT-5116: Fix concurrent modification exception inside ChunkMapDistance
989f9b3d SPIGOT-4849: Fix server crash when accessing chunks during chunk load/unload/populate events
f554183c SPIGOT-5171: Don't fire PlayerTeleportEvent if not actually moving
2349feb8 SPIGOT-5163: Cancelling PlayerBucketFillEvent visually removes the targeted block
Spigot Changes:
9a643a6a Remove DataWatcher Locking
This makes it easier for downstream projects (forks) to replace the
version fetching system with their own. It is as simple as implementing
an interface and overriding the default implementation of
org.bukkit.UnsafeValues#getVersionFetcher()
It also makes it easier for us to organize things like the version
history feature.
Lastly I have updated the paper implementation to check against the site
API rather than against jenkins.
Tux pointed out the patch still has O(n^2) time complexity since
the sublist class in arraylist does not override clear() from
AbstractList, which uses a forward moving iterator to clear
the list.
Resolved by using a peek and poll from ArrayDeque.
This patch also removes the useless WeakHashMap which holds
the list (it mapped world->list) and replaces it with a
field on World.
Shane Freeder
Zach Brown
Spottedleaf