Rewrite chunk system (#8177)

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.

1 files changed, 57 insertions, 0 deletions

diff --git a/patches/server/0339-Guard-against-serializing-mismatching-chunk-coordina.patch b/patches/server/0339-Guard-against-serializing-mismatching-chunk-coordina.patch
new file mode 100644
index 0000000000..7018c6fabf
--- /dev/null
+++ b/patches/server/0339-Guard-against-serializing-mismatching-chunk-coordina.patch
@@ -0,0 +1,57 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Spottedleaf <[email protected]>
+Date: Fri, 27 Dec 2019 09:42:26 -0800
+Subject: [PATCH] Guard against serializing mismatching chunk coordinate
+
+Should help if something dumb happens
+
+diff --git a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkSerializer.java b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkSerializer.java
+index e59910540458ca912efea64d9f7cd212d63d110a..f4bf0ecde863f1795d764d8cc8d6525af02356ea 100644
+--- a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkSerializer.java
++++ b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkSerializer.java
+@@ -92,6 +92,18 @@ public class ChunkSerializer {
+ 
+     public ChunkSerializer() {}
+ 
++    // Paper start - guard against serializing mismatching coordinates
++    // TODO Note: This needs to be re-checked each update
++    public static ChunkPos getChunkCoordinate(CompoundTag chunkData) {
++        final int dataVersion = ChunkStorage.getVersion(chunkData);
++        if (dataVersion < 2842) { // Level tag is removed after this version
++            final CompoundTag levelData = chunkData.getCompound("Level");
++            return new ChunkPos(levelData.getInt("xPos"), levelData.getInt("zPos"));
++        } else {
++            return new ChunkPos(chunkData.getInt("xPos"), chunkData.getInt("zPos"));
++        }
++    }
++    // Paper end
+     // Paper start
+     public static final class InProgressChunkHolder {
+ 
+@@ -117,7 +129,7 @@ public class ChunkSerializer {
+     public static InProgressChunkHolder loadChunk(ServerLevel world, PoiManager poiStorage, ChunkPos chunkPos, CompoundTag nbt, boolean distinguish) {
+         java.util.ArrayDeque<Runnable> tasksToExecuteOnMain = new java.util.ArrayDeque<>();
+         // Paper end
+-        ChunkPos chunkcoordintpair1 = new ChunkPos(nbt.getInt("xPos"), nbt.getInt("zPos"));
++        ChunkPos chunkcoordintpair1 = new ChunkPos(nbt.getInt("xPos"), nbt.getInt("zPos")); // Paper - diff on change, see ChunkSerializer#getChunkCoordinate
+ 
+         if (!Objects.equals(chunkPos, chunkcoordintpair1)) {
+             ChunkSerializer.LOGGER.error("Chunk file at {} is in the wrong location; relocating. (Expected {}, got {})", new Object[]{chunkPos, chunkPos, chunkcoordintpair1});
+diff --git a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
+index f2539f2aab4086bc6772db9985ca9f75ff6a7c71..aa915195d4aab3e931a92bf844f6dc18a0a59b9e 100644
+--- a/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
++++ b/src/main/java/net/minecraft/world/level/chunk/storage/ChunkStorage.java
+@@ -178,6 +178,13 @@ public class ChunkStorage implements AutoCloseable {
+ 
+     // Paper start - async chunk io
+     public void write(ChunkPos chunkPos, CompoundTag nbt) throws IOException {
++        // Paper start
++        if (!chunkPos.equals(ChunkSerializer.getChunkCoordinate(nbt))) {
++            String world = (this instanceof net.minecraft.server.level.ChunkMap) ? ((net.minecraft.server.level.ChunkMap)this).level.getWorld().getName() : null;
++            throw new IllegalArgumentException("Chunk coordinate and serialized data do not have matching coordinates, trying to serialize coordinate " + chunkPos.toString()
++                + " but compound says coordinate is " + ChunkSerializer.getChunkCoordinate(nbt).toString() + (world == null ? " for an unknown world" : (" for world: " + world)));
++        }
++        // Paper end
+         this.regionFileCache.write(chunkPos, nbt);
+         // Paper end - Async chunk loading
+         if (this.legacyStructureHandler != null) {