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.

patches/server/MC-Utils.patch

@@ -856,6 +856,137 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        return this.map.values().iterator();
 +    }
 +}
+diff --git a/src/main/java/com/destroystokyo/paper/util/maplist/ReferenceList.java b/src/main/java/com/destroystokyo/paper/util/maplist/ReferenceList.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
+--- /dev/null
++++ b/src/main/java/com/destroystokyo/paper/util/maplist/ReferenceList.java
+@@ -0,0 +0,0 @@
++package com.destroystokyo.paper.util.maplist;
++
++import it.unimi.dsi.fastutil.objects.Reference2IntOpenHashMap;
++import java.util.Arrays;
++import java.util.Iterator;
++import java.util.NoSuchElementException;
++
++/**
++ * @author Spottedleaf
++ */
++public final class ReferenceList<E> implements Iterable<E> {
++
++    protected final Reference2IntOpenHashMap<E> referenceToIndex = new Reference2IntOpenHashMap<>(2, 0.8f);
++    {
++        this.referenceToIndex.defaultReturnValue(Integer.MIN_VALUE);
++    }
++
++    protected static final Object[] EMPTY_LIST = new Object[0];
++
++    protected Object[] references = EMPTY_LIST;
++    protected int count;
++
++    public int size() {
++        return this.count;
++    }
++
++    public boolean contains(final E obj) {
++        return this.referenceToIndex.containsKey(obj);
++    }
++
++    public boolean remove(final E obj) {
++        final int index = this.referenceToIndex.removeInt(obj);
++        if (index == Integer.MIN_VALUE) {
++            return false;
++        }
++
++        // move the object at the end to this index
++        final int endIndex = --this.count;
++        final E end = (E)this.references[endIndex];
++        if (index != endIndex) {
++            // not empty after this call
++            this.referenceToIndex.put(end, index); // update index
++        }
++        this.references[index] = end;
++        this.references[endIndex] = null;
++
++        return true;
++    }
++
++    public boolean add(final E obj) {
++        final int count = this.count;
++        final int currIndex = this.referenceToIndex.putIfAbsent(obj, count);
++
++        if (currIndex != Integer.MIN_VALUE) {
++            return false; // already in this list
++        }
++
++        Object[] list = this.references;
++
++        if (list.length == count) {
++            // resize required
++            list = this.references = Arrays.copyOf(list, (int)Math.max(4L, count * 2L)); // overflow results in negative
++        }
++
++        list[count] = obj;
++        this.count = count + 1;
++
++        return true;
++    }
++
++    public E getChecked(final int index) {
++        if (index < 0 || index >= this.count) {
++            throw new IndexOutOfBoundsException("Index: " + index + " is out of bounds, size: " + this.count);
++        }
++        return (E)this.references[index];
++    }
++
++    public E getUnchecked(final int index) {
++        return (E)this.references[index];
++    }
++
++    public Object[] getRawData() {
++        return this.references;
++    }
++
++    public void clear() {
++        this.referenceToIndex.clear();
++        Arrays.fill(this.references, 0, this.count, null);
++        this.count = 0;
++    }
++
++    @Override
++    public Iterator<E> iterator() {
++        return new Iterator<>() {
++            private E lastRet;
++            private int current;
++
++            @Override
++            public boolean hasNext() {
++                return this.current < ReferenceList.this.count;
++            }
++
++            @Override
++            public E next() {
++                if (this.current >= ReferenceList.this.count) {
++                    throw new NoSuchElementException();
++                }
++                return this.lastRet = (E)ReferenceList.this.references[this.current++];
++            }
++
++            @Override
++            public void remove() {
++                final E lastRet = this.lastRet;
++
++                if (lastRet == null) {
++                    throw new IllegalStateException();
++                }
++                this.lastRet = null;
++
++                ReferenceList.this.remove(lastRet);
++                --this.current;
++            }
++        };
++    }
++}
 diff --git a/src/main/java/com/destroystokyo/paper/util/misc/AreaMap.java b/src/main/java/com/destroystokyo/paper/util/misc/AreaMap.java
 new file mode 100644
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
@@ -4544,6 +4675,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +import net.minecraft.server.level.ChunkHolder;
 +import net.minecraft.server.level.ChunkMap;
 +import net.minecraft.server.level.ServerLevel;
++import net.minecraft.server.level.ServerPlayer;
 +import net.minecraft.server.level.TicketType;
 +import net.minecraft.world.entity.Entity;
 +import net.minecraft.world.level.ChunkPos;
@@ -4775,30 +4907,54 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +        }
 +    }
 +
-+    public static void onChunkBorder(LevelChunk chunk, ChunkHolder holder) {
++    public static void onChunkBorder(final LevelChunk chunk, final ChunkHolder holder) {
 +        chunk.playerChunk = holder;
 +    }
 +
-+    public static void onChunkNotBorder(LevelChunk chunk, ChunkHolder holder) {
++    public static void onChunkNotBorder(final LevelChunk chunk, final ChunkHolder holder) {
 +
 +    }
 +
-+    public static void onChunkTicking(LevelChunk chunk, ChunkHolder holder) {
++    public static void onChunkTicking(final LevelChunk chunk, final ChunkHolder holder) {
 +        chunk.level.getChunkSource().tickingChunks.add(chunk);
 +    }
 +
-+    public static void onChunkNotTicking(LevelChunk chunk, ChunkHolder holder) {
++    public static void onChunkNotTicking(final LevelChunk chunk, final ChunkHolder holder) {
 +        chunk.level.getChunkSource().tickingChunks.remove(chunk);
 +    }
 +
-+    public static void onChunkEntityTicking(LevelChunk chunk, ChunkHolder holder) {
++    public static void onChunkEntityTicking(final LevelChunk chunk, final ChunkHolder holder) {
 +        chunk.level.getChunkSource().entityTickingChunks.add(chunk);
 +    }
 +
-+    public static void onChunkNotEntityTicking(LevelChunk chunk, ChunkHolder holder) {
++    public static void onChunkNotEntityTicking(final LevelChunk chunk, final ChunkHolder holder) {
 +        chunk.level.getChunkSource().entityTickingChunks.remove(chunk);
 +    }
 +
++    public static ChunkHolder getUnloadingChunkHolder(final ServerLevel level, final int chunkX, final int chunkZ) {
++        return level.chunkSource.chunkMap.getUnloadingChunkHolder(chunkX, chunkZ);
++    }
++
++    public static int getSendViewDistance(final ServerPlayer player) {
++        return getLoadViewDistance(player);
++    }
++
++    public static int getLoadViewDistance(final ServerPlayer player) {
++        final ServerLevel level = player.getLevel();
++        if (level == null) {
++            return Bukkit.getViewDistance() + 1;
++        }
++        return level.chunkSource.chunkMap.getEffectiveViewDistance() + 1;
++    }
++
++    public static int getTickViewDistance(final ServerPlayer player) {
++        final ServerLevel level = player.getLevel();
++        if (level == null) {
++            return Bukkit.getSimulationDistance();
++        }
++        return level.chunkSource.chunkMap.distanceManager.getSimulationDistance();
++    }
++
 +    private ChunkSystem() {
 +        throw new RuntimeException();
 +    }
@@ -5904,6 +6060,19 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      }
  
      protected void purgeStaleTickets() {
+@@ -0,0 +0,0 @@ public abstract class DistanceManager {
+         this.playerTicketManager.updateViewDistance(viewDistance);
+     }
+ 
++    // Paper start
++    public int getSimulationDistance() {
++        return this.simulationDistance;
++    }
++    // Paper end
++
+     public void updateSimulationDistance(int simulationDistance) {
+         if (simulationDistance != this.simulationDistance) {
+             this.simulationDistance = simulationDistance;
 @@ -0,0 +0,0 @@ public abstract class DistanceManager {
      }
  
@@ -6339,6 +6508,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      public String kickLeaveMessage = null; // SPIGOT-3034: Forward leave message to PlayerQuitEvent
      // CraftBukkit end
  
++    public boolean isRealPlayer; // Paper
 +    public final com.destroystokyo.paper.util.misc.PooledLinkedHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> cachedSingleHashSet; // Paper
 +
      public ServerPlayer(MinecraftServer server, ServerLevel world, GameProfile profile, @Nullable ProfilePublicKey publicKey) {
@@ -6396,6 +6566,18 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      @Override
      public BlockState getBlockState(BlockPos pos) {
          return this.getChunk(SectionPos.blockToSectionCoord(pos.getX()), SectionPos.blockToSectionCoord(pos.getZ())).getBlockState(pos);
+diff --git a/src/main/java/net/minecraft/server/players/PlayerList.java b/src/main/java/net/minecraft/server/players/PlayerList.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/server/players/PlayerList.java
++++ b/src/main/java/net/minecraft/server/players/PlayerList.java
+@@ -0,0 +0,0 @@ public abstract class PlayerList {
+     }
+ 
+     public void placeNewPlayer(Connection connection, ServerPlayer player) {
++        player.isRealPlayer = true; // Paper
+         GameProfile gameprofile = player.getGameProfile();
+         GameProfileCache usercache = this.server.getProfileCache();
+         Optional<GameProfile> optional = usercache.get(gameprofile.getId());
 diff --git a/src/main/java/net/minecraft/util/thread/BlockableEventLoop.java b/src/main/java/net/minecraft/util/thread/BlockableEventLoop.java
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
 --- a/src/main/java/net/minecraft/util/thread/BlockableEventLoop.java
@@ -6864,7 +7046,6 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      // CraftBukkit end
  
 +    // Paper start
-+    public final com.destroystokyo.paper.util.maplist.EntityList entities = new com.destroystokyo.paper.util.maplist.EntityList();
 +    public @Nullable ChunkHolder playerChunk;
 +
 +    static final int NEIGHBOUR_CACHE_RADIUS = 3;