From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <spottedleaf@spottedleaf.dev>
Date: Sat, 19 Sep 2020 15:29:16 -0700
Subject: [PATCH] Do not allow ticket level changes while unloading
 playerchunks

Sync loading the chunk at this stage would cause it to load
older data, as well as screwing our region state.

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 4a36952d81b92ed3cf8b5be8cbb6f0353d64a6d7..65b58b8a88a72c27bd10387a46dd3822c376ccd3 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -293,6 +293,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     }
     // Paper end
 
+    boolean unloadingPlayerChunk = false; // Paper - do not allow ticket level changes while unloading chunks
     public ChunkMap(ServerLevel world, LevelStorageSource.LevelStorageAccess session, DataFixer dataFixer, StructureManager structureManager, Executor executor, BlockableEventLoop<Runnable> mainThreadExecutor, LightChunkGetter chunkProvider, ChunkGenerator chunkGenerator, ChunkProgressListener worldGenerationProgressListener, ChunkStatusUpdateListener chunkStatusChangeListener, Supplier<DimensionDataStorage> persistentStateManagerFactory, int viewDistance, boolean dsync) {
         super(session.getDimensionPath(world.dimension()).resolve("region"), dataFixer, dsync);
         this.visibleChunkMap = this.updatingChunkMap.clone();
@@ -649,6 +650,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 
     @Nullable
     ChunkHolder updateChunkScheduling(long pos, int level, @Nullable ChunkHolder holder, int k) {
+        if (this.unloadingPlayerChunk) { net.minecraft.server.MinecraftServer.LOGGER.fatal("Cannot tick distance manager while unloading playerchunks", new Throwable()); throw new IllegalStateException("Cannot tick distance manager while unloading playerchunks"); } // Paper
         if (k > ChunkMap.MAX_CHUNK_DISTANCE && level > ChunkMap.MAX_CHUNK_DISTANCE) {
             return holder;
         } else {
@@ -861,6 +863,12 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
             if (completablefuture1 != completablefuture) {
                 this.scheduleUnload(pos, holder);
             } else {
+                // Paper start - do not allow ticket level changes while unloading chunks
+                org.spigotmc.AsyncCatcher.catchOp("playerchunk unload");
+                boolean unloadingBefore = this.unloadingPlayerChunk;
+                this.unloadingPlayerChunk = true;
+                try {
+                    // Paper end - do not allow ticket level changes while unloading chunks
                 // Paper start
                 boolean removed;
                 if ((removed = this.pendingUnloads.remove(pos, holder)) && ichunkaccess != null) {
@@ -897,6 +905,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                         this.regionManagers.get(index).removeChunk(holder.pos.x, holder.pos.z);
                     }
                 } // Paper end
+                } finally { this.unloadingPlayerChunk = unloadingBefore; } // Paper - do not allow ticket level changes while unloading chunks
 
             }
         };
diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index d1d6f4b75e807c8ea485cadd04a3ad1fc7d587bf..f871b8569f9812ee93b16fe9e45ea1a1c4f8f4aa 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -820,6 +820,7 @@ public class ServerChunkCache extends ChunkSource {
 
     public boolean runDistanceManagerUpdates() {
         if (distanceManager.delayDistanceManagerTick) return false; // Paper - Chunk priority
+        if (this.chunkMap.unloadingPlayerChunk) { net.minecraft.server.MinecraftServer.LOGGER.fatal("Cannot tick distance manager while unloading playerchunks", new Throwable()); throw new IllegalStateException("Cannot tick distance manager while unloading playerchunks"); } // Paper
         boolean flag = this.distanceManager.runAllUpdates(this.chunkMap);
         boolean flag1 = this.chunkMap.promoteChunkMap();