PaperMC/Spigot-Server-Patches/0091-Optimize-Chunk-Unload-Queue.patch

From 5036fed452975d8857105532162be561fcd8effc Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 18 Mar 2016 17:57:25 -0400
Subject: [PATCH] Optimize Chunk Unload Queue

Removing chunks from the unload queue when performing chunk lookups is a costly activity.

It drastically slows down server performance as many methods call getChunkAt, resulting in a bandaid
to skip removing chunks from the unload queue.

This patch optimizes the unload queue to instead use a boolean on the Chunk object itself to mark
if the chunk is active, and then insert into a LinkedList queue.

The benefits here is that all chunk unload queue actions are now O(1) constant time.

A LinkedList will never need to resize, and can be removed from in constant time when
used in a queue like method.

We mark the chunk as active in many places that notify it is still being used, so that
when the chunk unload queue reaches that chunk, and sees the chunk became active again,
it will skip it and move to next.

diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
index b6d84d7..a4c0b4e 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -55,6 +55,8 @@ public class Chunk {
     // Keep this synced with entitySlices.add() and entitySlices.remove()
     private final int[] itemCounts = new int[16];
     private final int[] inventoryEntityCounts = new int[16];
+    public boolean isChunkActive = true;
+    public boolean isInUnloadQueue = false;
     // Paper end
 
     // CraftBukkit start - Neighbor loaded cache for chunk lighting and entity ticking
@@ -780,6 +782,7 @@ public class Chunk {
     }
 
     public void addEntities() {
+        isChunkActive = true; // Paper
         this.i = true;
         this.world.b(this.tileEntities.values());
 
@@ -798,6 +801,7 @@ public class Chunk {
     }
 
     public void removeEntities() {
+        isChunkActive = false; // Paper
         this.i = false;
         Iterator iterator = this.tileEntities.values().iterator();
 
diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index 9ef6246..f62a2c7 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -21,7 +21,7 @@ import org.bukkit.event.world.ChunkUnloadEvent;
 public class ChunkProviderServer implements IChunkProvider {
 
     private static final Logger a = LogManager.getLogger();
-    public final LongHashSet unloadQueue = new LongHashSet(); // CraftBukkit - LongHashSet
+    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
@@ -79,18 +79,18 @@ public class ChunkProviderServer implements IChunkProvider {
 
     // CraftBukkit start - Add async variant, provide compatibility
     public Chunk getOrCreateChunkFast(int x, int z) {
-        Chunk chunk = chunks.get(LongHash.toLong(x, z));
-        return (chunk == null) ? getChunkAt(x, z) : chunk;
+        return getChunkAt(x, z); // Paper
     }
 
     public Chunk getChunkIfLoaded(int x, int z) {
-        return chunks.get(LongHash.toLong(x, z));
+        return getLoadedChunkAt(x, z); // Paper - Bukkit has a duplicate method now.
     }
 
     public Chunk getLoadedChunkAt(int i, int j) {
         Chunk chunk = chunks.get(LongHash.toLong(i, j)); // CraftBukkit
 
         this.unloadQueue.remove(i, j); // CraftBukkit
+        if (chunk != null) { chunk.isChunkActive = true; }// Paper
         return chunk;
     }
 
@@ -151,6 +151,7 @@ public class ChunkProviderServer implements IChunkProvider {
             runnable.run();
         }
 
+        chunk.isChunkActive = true; // Paper
         return chunk;
     }
 
@@ -300,10 +301,17 @@ public class ChunkProviderServer implements IChunkProvider {
         if (!this.world.savingDisabled) {
             // CraftBukkit start
             Server server = this.world.getServer();
-            for (int i = 0; i < 100 && !this.unloadQueue.isEmpty(); ++i) {
-                long chunkcoordinates = this.unloadQueue.popFirst();
-                Chunk chunk = this.chunks.get(chunkcoordinates);
-                if (chunk == null) continue;
+            // Paper start
+            final Iterator<Chunk> iterator = this.unloadQueue.iterator();
+            for (int i = 0; i < 100 && iterator.hasNext(); ++i) {
+                Chunk chunk = iterator.next();
+                iterator.remove();
+                long chunkcoordinates = LongHash.toLong(chunk.locX, chunk.locZ);
+                chunk.isInUnloadQueue = false;
+                if (chunk.isChunkActive) {
+                    continue;
+                }
+                // Paper end
 
                 ChunkUnloadEvent event = new ChunkUnloadEvent(chunk.bukkitChunk);
                 server.getPluginManager().callEvent(event);
@@ -367,4 +375,22 @@ public class ChunkProviderServer implements IChunkProvider {
     public boolean e(int i, int j) {
         return this.chunks.containsKey(LongHash.toLong(i, j)); // CraftBukkit
     }
+
+    // Paper start
+    public class ChunkUnloadQueue extends java.util.LinkedList<Chunk> {
+        public void remove(int x, int z) {
+            // nothing! Just to reduce diff
+        }
+        public void add(int x, int z) {
+            final Chunk chunk = chunks.get(LongHash.toLong(x, z));
+            if (chunk != null) {
+                chunk.isChunkActive = false;
+                if (!chunk.isInUnloadQueue) {
+                    chunk.isInUnloadQueue = true;
+                    add(chunk);
+                }
+            }
+        }
+    }
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/server/SpawnerCreature.java b/src/main/java/net/minecraft/server/SpawnerCreature.java
index 63e118d..721bcae 100644
--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
+++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
@@ -28,7 +28,7 @@ public final class SpawnerCreature {
             Long coord = it.next();
             int x = LongHash.msw( coord );
             int z = LongHash.lsw( coord );
-            if ( !((ChunkProviderServer)server.chunkProvider).unloadQueue.contains( coord ) && server.isChunkLoaded( x, z, true ) )
+            if ( server.isChunkLoaded( x, z, true ) ) // Paper
             {
                 i += server.getChunkAt( x, z ).entityCount.get( oClass );
             }
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index 40338c0..bd28154 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -302,7 +302,7 @@ public class CraftWorld implements World {
             world.timings.syncChunkLoadTimer.startTiming(); // Spigot
             chunk = world.getChunkProviderServer().getOrLoadChunkAt(x, z);
             world.timings.syncChunkLoadTimer.stopTiming(); // Spigot
-        }
+        } else { chunk.isChunkActive = true; } // Paper
         return chunk != null;
     }
 
@@ -1538,7 +1538,7 @@ public class CraftWorld implements World {
             }
 
             // Already unloading?
-            if (cps.unloadQueue.contains(chunk.locX, chunk.locZ)) {
+            if (!chunk.isChunkActive) { // Paper
                 continue;
             }
 
-- 
2.7.4