Entity add to world fixes - #1223

1) Chunk Registration might kill an entity, don't add it to the world if it did!

2) By default, entities are added to the world per slice iteration.
This opens risk of the slices being manipulated during chunk add if an
EntityAddToWorldEvent spawns an entity into this chunk.
Fix this by differing entity add to world for all entities at the same time

3) If a duplicate entity is attempted to add to the world of an entity, and
the original entity is dead, overwrite it as the logic does for unloaod queued entities.

Should hopefully finish up issues with #1223

Spigot-Server-Patches/0341-Prevent-Saving-Bad-entities-to-chunks.patch

@@ -1,4 +1,4 @@
-From 186657866775b48d9c845b8066339b463c4f88ad Mon Sep 17 00:00:00 2001
+From 354cae3bd5b0d32cf8c1f8cebdff763013606fd5 Mon Sep 17 00:00:00 2001
 From: Aikar <aikar@aikar.co>
 Date: Thu, 26 Jul 2018 00:11:12 -0400
 Subject: [PATCH] Prevent Saving Bad entities to chunks
@@ -56,32 +56,6 @@ index bcce5e8b7e..bad287fca4 100644
  
          nbttagcompound.set("Entities", nbttaglist1);
          NBTTagList nbttaglist2 = new NBTTagList();
-diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
-index c53e77b821..2a4405638e 100644
---- a/src/main/java/net/minecraft/server/World.java
-+++ b/src/main/java/net/minecraft/server/World.java
-@@ -1204,7 +1204,7 @@ public abstract class World implements IBlockAccess {
-             }
- 
-             this.getChunkAt(i, j).a(entity);
--            this.entityList.add(entity);
-+            if (!entity.dead) this.entityList.add(entity); // Paper - don't add dead entities, chunk registration may of killed it
-             this.b(entity);
-             return true;
-         }
-diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
-index 1244baf45a..1763d9f94d 100644
---- a/src/main/java/net/minecraft/server/WorldServer.java
-+++ b/src/main/java/net/minecraft/server/WorldServer.java
-@@ -1173,7 +1173,7 @@ public class WorldServer extends World implements IAsyncTaskHandler {
-             if (this.entitiesByUUID.containsKey(uuid)) {
-                 Entity entity1 = (Entity) this.entitiesByUUID.get(uuid);
- 
--                if (this.f.contains(entity1)) {
-+                if (this.f.contains(entity1) || entity1.dead) { // Paper - overwrite the current dead one
-                     this.f.remove(entity1);
-                 } else {
-                     if (!(entity instanceof EntityHuman)) {
 -- 
 2.18.0
 

Spigot-Server-Patches/0348-Entity-add-to-world-fixes.patch

@@ -0,0 +1,87 @@
+From 65255110b50ca2fb51d2b95fa1cc8c5f61da88e8 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Fri, 3 Aug 2018 22:47:46 -0400
+Subject: [PATCH] Entity add to world fixes
+
+1) Chunk Registration might kill an entity, don't add it to the world if it did!
+
+2) By default, entities are added to the world per slice iteration.
+This opens risk of the slices being manipulated during chunk add if an
+EntityAddToWorldEvent spawns an entity into this chunk.
+Fix this by differing entity add to world for all entities at the same time
+
+3) If a duplicate entity is attempted to add to the world of an entity, and
+the original entity is dead, overwrite it as the logic does for unloaod queued entities.
+
+diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
+index f41f282848..c6f47d4089 100644
+--- a/src/main/java/net/minecraft/server/Chunk.java
++++ b/src/main/java/net/minecraft/server/Chunk.java
+@@ -888,6 +888,7 @@ public class Chunk {
+         this.world.b(this.tileEntities.values());
+         List[] aentityslice = this.entitySlices; // Spigot
+         int i = aentityslice.length;
++        List<Entity> toAdd = new java.util.ArrayList<>(32); // Paper
+ 
+         for (int j = 0; j < i; ++j) {
+             List entityslice = aentityslice[j]; // Spigot
+@@ -934,10 +935,12 @@ public class Chunk {
+                     thisChunk.put(entity.uniqueID, entity);
+                 }
+             }
+-            // Paper end
+ 
+-            this.world.a((Collection) entityslice);
++            //this.world.a((Collection) entityslice); // Move down, add all entities at same time
++            toAdd.addAll(entityslice);
++            // Paper end
+         }
++        this.world.addChunkEntities(toAdd); // Paper - add all at same time to avoid entities adding to world modifying slice state
+ 
+     }
+ 
+diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
+index 2ad7c75d2b..c04a9d5a09 100644
+--- a/src/main/java/net/minecraft/server/World.java
++++ b/src/main/java/net/minecraft/server/World.java
+@@ -1204,6 +1204,7 @@ public abstract class World implements IBlockAccess {
+             }
+ 
+             this.getChunkAt(i, j).a(entity);
++            if (entity.dead) return false; // Paper - don't add dead entities, chunk registration may of killed it
+             this.entityList.add(entity);
+             this.b(entity);
+             return true;
+@@ -2743,6 +2744,7 @@ public abstract class World implements IBlockAccess {
+         return i;
+     }
+ 
++    public void addChunkEntities(Collection<Entity> collection) { a(collection); } // Paper - OBFHELPER
+     public void a(Collection<Entity> collection) {
+         org.spigotmc.AsyncCatcher.catchOp( "entity world add"); // Spigot
+         // CraftBukkit start
+@@ -2752,7 +2754,7 @@ public abstract class World implements IBlockAccess {
+         while (iterator.hasNext()) {
+             Entity entity = (Entity) iterator.next();
+ 
+-            if (entity == null) {
++            if (entity == null || entity.dead || entity.valid) { // Paper - prevent adding already added or dead entities
+                 continue;
+             }
+             this.entityList.add(entity);
+diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
+index 1244baf45a..a14b5e0618 100644
+--- a/src/main/java/net/minecraft/server/WorldServer.java
++++ b/src/main/java/net/minecraft/server/WorldServer.java
+@@ -1173,7 +1173,7 @@ public class WorldServer extends World implements IAsyncTaskHandler {
+             if (this.entitiesByUUID.containsKey(uuid)) {
+                 Entity entity1 = (Entity) this.entitiesByUUID.get(uuid);
+ 
+-                if (this.f.contains(entity1)) {
++                if (this.f.contains(entity1) || entity1.dead) { // Paper - if dupe is dead, overwrite
+                     this.f.remove(entity1);
+                 } else {
+                     if (!(entity instanceof EntityHuman)) {
+-- 
+2.18.0
+