From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Thu, 27 Aug 2015 01:15:02 -0400
Subject: [PATCH] Optimize Chunk Access

getting a loaded chunk is one of the most hottest pieces of code in the game.
getChunkAt is called for the same chunk multiple times in a row, often from getType();

Optimize this look up by using a Last Access cache.

diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -0,0 +0,0 @@ public class Chunk {
     private boolean i;
     public final World world;
     public final int[] heightMap;
+    public final long chunkKey; // Paper
     public final int locX;
     public final int locZ;
     private boolean l;
@@ -0,0 +0,0 @@ public class Chunk {
         this.world = world;
         this.locX = i;
         this.locZ = j;
+        this.chunkKey = org.bukkit.craftbukkit.util.LongHash.toLong(this.locX, this.locZ); // Paper
         this.heightMap = new int[256];
 
         for (int k = 0; k < this.entitySlices.length; ++k) {
diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -0,0 +0,0 @@ public class ChunkProviderServer implements IChunkProvider {
     public final ChunkUnloadQueue unloadQueue = new ChunkUnloadQueue(); // CraftBukkit - LongHashSet // Paper -> ChunkUnloadQueue
     public final ChunkGenerator chunkGenerator; // CraftBukkit - public
     private final IChunkLoader chunkLoader;
-    public LongObjectHashMap<Chunk> chunks = new LongObjectHashMap<Chunk>(); // CraftBukkit
+    // Paper start
+    protected Chunk lastChunkByPos = null;
+    public LongObjectHashMap<Chunk> chunks = new LongObjectHashMap<Chunk>() {
+        @Override
+        public Chunk get(long key) {
+            if (lastChunkByPos != null && key == lastChunkByPos.chunkKey) {
+                return lastChunkByPos;
+            }
+            return lastChunkByPos = super.get(key);
+        }
+    }; // CraftBukkit
+    // Paper end
     // private final LongHashMap<Chunk> chunks = new LongHashMap();
     // private final List<Chunk> chunkList = Lists.newArrayList();
     public final WorldServer world;
@@ -0,0 +0,0 @@ public class ChunkProviderServer implements IChunkProvider {
 
             Chunk c = chunks.get(LongHash.toLong(i, j));
             if (c != null) {
+                world.testResetChunkCache(c); // Paper
                 c.mustSave = true;
             }
             // CraftBukkit end
@@ -0,0 +0,0 @@ public class ChunkProviderServer implements IChunkProvider {
                         chunk.removeEntities();
                         this.saveChunk(chunk);
                         this.saveChunkNOP(chunk);
+                        world.testResetChunkCache(chunk); // Paper
                         this.chunks.remove(chunkcoordinates); // CraftBukkit
                     }
 
diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/World.java
+++ b/src/main/java/net/minecraft/server/World.java
@@ -0,0 +0,0 @@ public abstract class World implements IBlockAccess {
     public Chunk getChunkIfLoaded(BlockPosition blockposition) {
         return this.chunkProvider.getLoadedChunkAt(blockposition.getX() >> 4, blockposition.getZ() >> 4);
     }
+
+    public void testResetChunkCache(Chunk chunk) {
+        if (chunk == ((ChunkProviderServer) chunkProvider).lastChunkByPos) {
+            ((ChunkProviderServer) chunkProvider).lastChunkByPos = null;
+        }
+    }
     // Paper end
 
     public Chunk getChunkIfLoaded(int x, int z) {
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -0,0 +0,0 @@ public class WorldServer extends World implements IAsyncTaskHandler {
     // CraftBukkit end
 
     public void doTick() {
+        ((ChunkProviderServer) chunkProvider).lastChunkByPos = null; // Paper
         super.doTick();
         if (this.getWorldData().isHardcore() && this.getDifficulty() != EnumDifficulty.HARD) {
             this.getWorldData().setDifficulty(EnumDifficulty.HARD);
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -0,0 +0,0 @@ public class CraftWorld implements World {
 
         world.getChunkProviderServer().unloadQueue.remove(x, z);
         world.getChunkProviderServer().chunks.remove(LongHash.toLong(x, z));
+        world.testResetChunkCache(chunk); // Paper
 
         // Update neighbor counts
         for (int xx = -2; xx < 3; xx++) {
--