Paper/Spigot-Server-Patches/0250-Add-some-Debug-to-Chunk-Entity-slices.patch

From 0000000000000000000000000000000000000000 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 90b2a891c5bfa26ab1ff6738f58719a10d5cbed6..8b9454fd44fe1d14eb6d46f772be56937c99595a 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -514,6 +514,25 @@ public class Chunk implements IChunkAccess {
         if (k >= this.entitySlices.length) {
             k = this.entitySlices.length - 1;
         }
+        // Paper - remove from any old list if its in one
+        List<Entity> nextSlice = this.entitySlices[k]; // the next list to be added to
+        List<Entity> currentSlice = entity.entitySlice;
+        if (nextSlice == currentSlice) {
+            if (World.DEBUG_ENTITIES) MinecraftServer.LOGGER.warn("Entity was already in this chunk!" + entity, new Throwable());
+            return; // ??? silly plugins
+        }
+        if (currentSlice != null && currentSlice.contains(entity)) {
+            // Still in an old chunk...
+            if (World.DEBUG_ENTITIES) MinecraftServer.LOGGER.warn("Entity is still in another chunk!" + entity, new Throwable());
+            Chunk chunk = entity.getCurrentChunk();
+            if (chunk != null) {
+                chunk.removeEntity(entity);
+            } else {
+                removeEntity(entity);
+            }
+            currentSlice.remove(entity); // Just incase the above did not remove from the previous slice
+        }
+        // Paper end
 
         if (!entity.inChunk || entity.getCurrentChunk() != this) entityCounts.increment(entity.getMinecraftKeyString()); // Paper
         entity.inChunk = true;
@@ -523,6 +542,7 @@ public class Chunk implements IChunkAccess {
         entity.chunkZ = this.loc.z;
         this.entities.add(entity); // Paper - per chunk entity list
         this.entitySlices[k].add(entity);
+        entity.entitySlice = this.entitySlices[k]; // Paper
         this.markDirty(); // Paper
     }
 
@@ -547,6 +567,10 @@ public class Chunk implements IChunkAccess {
 
         // Paper start
         if (entity.currentChunk != null && entity.currentChunk.get() == this) entity.setCurrentChunk(null);
+        if (entitySlices[i] == entity.entitySlice) {
+            entity.entitySlice = null;
+            entity.inChunk = false;
+        }
         if (!this.entitySlices[i].remove(entity)) {
             return;
         }
diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 91b450da31b972e2251382cd068a818a6bd70c1e..a331a62be48c3d9f5247817dfeeaba923aed5f57 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -71,6 +71,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
             }
         }
     };
+    List<Entity> entitySlice = null;
     // Paper end
 
     public com.destroystokyo.paper.loottable.PaperLootableInventoryData lootableData; // Paper