From 6c6bd2c67ce8837dcb7b21a2468a0e5e70b9531d Mon Sep 17 00:00:00 2001
From: md_5 <git@md-5.net>
Date: Mon, 10 Mar 2014 09:03:28 +1100
Subject: [PATCH] Guard Entity List


diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
index a6bd744..2cc87d0 100644
--- a/src/main/java/net/minecraft/server/World.java
+++ b/src/main/java/net/minecraft/server/World.java
@@ -33,7 +33,32 @@ public abstract class World implements IBlockAccess {
 
     private int a = 63;
     protected boolean d;
-    public final List<Entity> entityList = Lists.newArrayList();
+    // Spigot start - guard entity list from removals
+    public final List<Entity> entityList = new java.util.ArrayList<Entity>()
+    {
+        @Override
+        public Entity remove(int index)
+        {
+            guard();
+            return super.remove( index );
+        }
+
+        @Override
+        public boolean remove(Object o)
+        {
+            guard();
+            return super.remove( o );
+        }
+
+        private void guard()
+        {
+            if ( guardEntityList )
+            {
+                throw new java.util.ConcurrentModificationException();
+            }
+        }
+    };
+    // Spigot end
     protected final List<Entity> f = Lists.newArrayList();
     public final List<TileEntity> tileEntityList = Lists.newArrayList();
     public final List<TileEntity> tileEntityListTick = Lists.newArrayList();
@@ -101,6 +126,7 @@ public abstract class World implements IBlockAccess {
     public final org.spigotmc.SpigotWorldConfig spigotConfig; // Spigot
 
     public final SpigotTimings.WorldTimingsHandler timings; // Spigot
+    private boolean guardEntityList; // Spigot
 
     public CraftWorld getWorld() {
         return this.world;
@@ -1312,6 +1338,7 @@ public abstract class World implements IBlockAccess {
 
         org.spigotmc.ActivationRange.activateEntities(this); // Spigot
         timings.entityTick.startTiming(); // Spigot
+        guardEntityList = true; // Spigot
         // CraftBukkit start - Use field for loop variable
         for (this.tickPosition = 0; this.tickPosition < this.entityList.size(); ++this.tickPosition) {
             entity = (Entity) this.entityList.get(this.tickPosition);
@@ -1350,12 +1377,15 @@ public abstract class World implements IBlockAccess {
                     this.getChunkAt(j, l).b(entity);
                 }
 
+                guardEntityList = false; // Spigot
                 this.entityList.remove(this.tickPosition--); // CraftBukkit - Use field for loop variable
+                guardEntityList = true; // Spigot
                 this.c(entity);
             }
 
             this.methodProfiler.b();
         }
+        guardEntityList = false; // Spigot
 
         timings.entityTick.stopTiming(); // Spigot
         this.methodProfiler.c("blockEntities");
-- 
2.5.0