From eb8942dae2dd6dbc8a32b05c0a502a4a507d7233 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/ChunkMap.java b/src/main/java/net/minecraft/server/ChunkMap.java
index 4b8b77710b..71ddaf591e 100644
--- a/src/main/java/net/minecraft/server/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/ChunkMap.java
@@ -15,6 +15,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
 
     public Chunk a(long i, Chunk chunk) {
         chunk.world.timings.syncChunkLoadPostTimer.startTiming(); // Paper
+        lastChunkByPos = chunk; // Paper
         Chunk chunk1 = (Chunk) super.put(i, chunk);
         ChunkCoordIntPair chunkcoordintpair = new ChunkCoordIntPair(i);
 
@@ -22,7 +23,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
             for (int k = chunkcoordintpair.z - 1; k <= chunkcoordintpair.z + 1; ++k) {
                 if (j != chunkcoordintpair.x || k != chunkcoordintpair.z) {
                     long l = ChunkCoordIntPair.a(j, k);
-                    Chunk chunk2 = (Chunk) this.get(l);
+                    Chunk chunk2 = (Chunk) super.get(l);  // Paper - use super to avoid polluting last access cache
 
                     if (chunk2 != null) {
                         chunk.H();
@@ -40,7 +41,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
                     continue;
                 }
 
-                Chunk neighbor = this.get(ChunkCoordIntPair.a(chunkcoordintpair.x + x, chunkcoordintpair.z + z));
+                Chunk neighbor = super.get(ChunkCoordIntPair.a(chunkcoordintpair.x + x, chunkcoordintpair.z + z)); // Paper - use super to avoid polluting last access cache
                 if (neighbor != null) {
                     neighbor.setNeighborLoaded(-x, -z);
                     chunk.setNeighborLoaded(x, z);
@@ -64,7 +65,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
         for (int j = chunkcoordintpair.x - 1; j <= chunkcoordintpair.x + 1; ++j) {
             for (int k = chunkcoordintpair.z - 1; k <= chunkcoordintpair.z + 1; ++k) {
                 if (j != chunkcoordintpair.x || k != chunkcoordintpair.z) {
-                    Chunk chunk1 = (Chunk) this.get(ChunkCoordIntPair.a(j, k));
+                    Chunk chunk1 = (Chunk) super.get(ChunkCoordIntPair.a(j, k)); // Paper - use super to avoid polluting last access cache
 
                     if (chunk1 != null) {
                         chunk1.I();
@@ -73,8 +74,22 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
             }
         }
 
+        // Paper start
+        if (lastChunkByPos != null && i == lastChunkByPos.chunkKey) {
+            lastChunkByPos = null;
+        }
         return chunk;
     }
+    private Chunk lastChunkByPos = null;
+
+    @Override
+    public Chunk get(long l) {
+        if (lastChunkByPos != null && l == lastChunkByPos.chunkKey) {
+            return lastChunkByPos;
+        }
+        return lastChunkByPos = super.get(l);
+    }
+    // Paper end
 
     public Chunk a(Object object) {
         return this.a(((Long) object).longValue());
diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index d16fc452e3..2d10f4aa37 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -78,15 +78,16 @@ public class ChunkProviderServer implements IChunkProvider {
         Chunk chunk;
 
         synchronized (this.chunkLoader) {
-            if (this.lastChunk != null && this.lastChunk.getPos().x == i && this.lastChunk.getPos().z == j) {
+            // Paper start - remove vanilla lastChunk, we do it more accurately
+            /* if (this.lastChunk != null && this.lastChunk.locX == i && this.lastChunk.locZ == j) {
                 return this.lastChunk;
-            }
+            }*/ // Paper end
 
             long k = ChunkCoordIntPair.a(i, j);
 
             chunk = (Chunk) this.chunks.get(k);
             if (chunk != null) {
-                this.lastChunk = chunk;
+                //this.lastChunk = chunk; // Paper remove vanilla lastChunk
                 return chunk;
             }
 
@@ -198,7 +199,7 @@ public class ChunkProviderServer implements IChunkProvider {
             }
 
             this.chunks.put(k, chunk);
-            this.lastChunk = chunk;
+            //this.lastChunk = chunk; // Paper
         }
 
         this.asyncTaskHandler.postToMainThread(chunk::addEntities);
@@ -343,7 +344,7 @@ public class ChunkProviderServer implements IChunkProvider {
                 this.saveChunk(chunk, true); // Spigot
             }
             this.chunks.remove(chunk.chunkKey);
-            this.lastChunk = null;
+            // this.lastChunk = null; // Paper
         }
         return true;
     }
-- 
2.19.1