From d155366b5420147429817f3cce515518bcbdcf58 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Mon, 23 Jul 2018 22:55:27 -0400
Subject: [PATCH] Add some debug for entity slices

If we find any entity in an unexpected state, log it so we can discover
what potentially put it in that state to relate to issue #1223
---
 ...dd-some-Debug-to-Chunk-Entity-slices.patch | 77 +++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 Spigot-Server-Patches/0340-Add-some-Debug-to-Chunk-Entity-slices.patch

diff --git a/Spigot-Server-Patches/0340-Add-some-Debug-to-Chunk-Entity-slices.patch b/Spigot-Server-Patches/0340-Add-some-Debug-to-Chunk-Entity-slices.patch
new file mode 100644
index 000000000..e59455dc4
--- /dev/null
+++ b/Spigot-Server-Patches/0340-Add-some-Debug-to-Chunk-Entity-slices.patch
@@ -0,0 +1,77 @@
+From 80a062ecc95b8346f6a9161e375e41d5f5df3882 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Mon, 23 Jul 2018 22:44:23 -0400
+Subject: [PATCH] Add some Debug to Chunk Entity slices
+
+If we detect unexpected state, log and try to recover
+
+This should hopefully avoid duplicate entities ever being created
+if the entity was to end up in 2 different chunk slices
+
+diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
+index 6de053781..be0b411e5 100644
+--- a/src/main/java/net/minecraft/server/Chunk.java
++++ b/src/main/java/net/minecraft/server/Chunk.java
+@@ -681,8 +681,33 @@ public class Chunk {
+         entity.ab = this.locX;
+         entity.ac = k;
+         entity.ad = this.locZ;
+-        this.entitySlices[k].add(entity);
++
+         // Paper start
++        List<Entity> entitySlice = this.entitySlices[k];
++        boolean inThis = entitySlice.contains(entity);
++        if (entity.entitySlice != null || inThis) {
++            if (entity.entitySlice == entitySlice || inThis) {
++                LogManager.getLogger().warn(entity + " was already in this chunk section! Report this to https://github.com/PaperMC/Paper/issues/1223");
++                new Throwable().printStackTrace();
++                return;
++            } else {
++                LogManager.getLogger().warn(entity + " is still in another ChunkSection! Report this to https://github.com/PaperMC/Paper/issues/1223");
++
++                Chunk chunk = entity.getCurrentChunk();
++                if (chunk != null) {
++                    if (chunk != this) {
++                        LogManager.getLogger().warn(entity + " was in another chunk at that! " + chunk.locX + "," + chunk.locZ);
++                    }
++                    chunk.removeEntity(entity);
++                } else {
++                    removeEntity(entity);
++                }
++                new Throwable().printStackTrace();
++            }
++        }
++        entity.entitySlice = entitySlice;
++        entitySlice.add(entity);
++
+         this.markDirty();
+         entity.setCurrentChunk(this);
+         entityCounts.increment(entity.entityKeyString);
+@@ -726,6 +751,12 @@ public class Chunk {
+ 
+         // Paper start
+         if (!this.entitySlices[i].remove(entity)) { return; }
++        if (entitySlices[i] == entity.entitySlice) {
++            entity.entitySlice = null;
++        } else {
++            LogManager.getLogger().warn(entity + " was removed from a entitySlice we did not expect. Report this to https://github.com/PaperMC/Paper/issues/1223");
++            new Throwable().printStackTrace();
++        }
+         this.markDirty();
+         entity.setCurrentChunk(null);
+         entityCounts.decrement(entity.entityKeyString);
+diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
+index 7188d0c99..b3120d7cc 100644
+--- a/src/main/java/net/minecraft/server/Entity.java
++++ b/src/main/java/net/minecraft/server/Entity.java
+@@ -59,6 +59,7 @@ public abstract class Entity implements ICommandListener, KeyedObject { // Paper
+             }
+         }
+     };
++    Object entitySlice = null;
+     // Paper end
+     static boolean isLevelAtLeast(NBTTagCompound tag, int level) {
+         return tag.hasKey("Bukkit.updateLevel") && tag.getInt("Bukkit.updateLevel") >= level;
+-- 
+2.18.0
+