Ensure chunk neighbor counts do not get desynced

Mojang was not checking that the chunk did not overwrite, or
was successfully removed.

We're seeing odd reports in #1561 that indicates issues around
this are having problems.

Spigot-Server-Patches/0078-Optimize-Chunk-Access.patch

@@ -1,4 +1,4 @@
-From 14e26ad623fc54b7f4e0c647f40b9cdcca79a88f Mon Sep 17 00:00:00 2001
+From eb8942dae2dd6dbc8a32b05c0a502a4a507d7233 Mon Sep 17 00:00:00 2001
 From: Aikar <aikar@aikar.co>
 Date: Thu, 27 Aug 2015 01:15:02 -0400
 Subject: [PATCH] Optimize Chunk Access
@@ -9,7 +9,7 @@ getChunkAt is called for the same chunk multiple times in a row, often from getT
 Optimize this look up by using a Last Access cache.
 
 diff --git a/src/main/java/net/minecraft/server/ChunkMap.java b/src/main/java/net/minecraft/server/ChunkMap.java
-index 4b8b77710b..df967ff07d 100644
+index 4b8b77710b..71ddaf591e 100644
 --- a/src/main/java/net/minecraft/server/ChunkMap.java
 +++ b/src/main/java/net/minecraft/server/ChunkMap.java
 @@ -15,6 +15,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
@@ -20,6 +20,33 @@ index 4b8b77710b..df967ff07d 100644
          Chunk chunk1 = (Chunk) super.put(i, chunk);
          ChunkCoordIntPair chunkcoordintpair = new ChunkCoordIntPair(i);
  
+@@ -22,7 +23,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+             for (int k = chunkcoordintpair.z - 1; k <= chunkcoordintpair.z + 1; ++k) {
+                 if (j != chunkcoordintpair.x || k != chunkcoordintpair.z) {
+                     long l = ChunkCoordIntPair.a(j, k);
+-                    Chunk chunk2 = (Chunk) this.get(l);
++                    Chunk chunk2 = (Chunk) super.get(l);  // Paper - use super to avoid polluting last access cache
+ 
+                     if (chunk2 != null) {
+                         chunk.H();
+@@ -40,7 +41,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+                     continue;
+                 }
+ 
+-                Chunk neighbor = this.get(ChunkCoordIntPair.a(chunkcoordintpair.x + x, chunkcoordintpair.z + z));
++                Chunk neighbor = super.get(ChunkCoordIntPair.a(chunkcoordintpair.x + x, chunkcoordintpair.z + z)); // Paper - use super to avoid polluting last access cache
+                 if (neighbor != null) {
+                     neighbor.setNeighborLoaded(-x, -z);
+                     chunk.setNeighborLoaded(x, z);
+@@ -64,7 +65,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+         for (int j = chunkcoordintpair.x - 1; j <= chunkcoordintpair.x + 1; ++j) {
+             for (int k = chunkcoordintpair.z - 1; k <= chunkcoordintpair.z + 1; ++k) {
+                 if (j != chunkcoordintpair.x || k != chunkcoordintpair.z) {
+-                    Chunk chunk1 = (Chunk) this.get(ChunkCoordIntPair.a(j, k));
++                    Chunk chunk1 = (Chunk) super.get(ChunkCoordIntPair.a(j, k)); // Paper - use super to avoid polluting last access cache
+ 
+                     if (chunk1 != null) {
+                         chunk1.I();
 @@ -73,8 +74,22 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
              }
          }
@@ -86,5 +113,5 @@ index d16fc452e3..2d10f4aa37 100644
          return true;
      }
 -- 
-2.19.0
+2.19.1
 

Spigot-Server-Patches/0396-Ensure-chunk-neighbor-counts-do-not-get-desynced.patch

@@ -0,0 +1,54 @@
+From 5d6a6cd178b5baef11c1a52c7f91bf71ef789da4 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Wed, 17 Oct 2018 22:31:54 -0400
+Subject: [PATCH] Ensure chunk neighbor counts do not get desynced
+
+Mojang was not checking that the chunk did not overwrite, or
+was successfully removed.
+
+We're seeing odd reports in #1561 that indicates issues around
+this are having problems.
+
+diff --git a/src/main/java/net/minecraft/server/ChunkMap.java b/src/main/java/net/minecraft/server/ChunkMap.java
+index 39ac032b0b..1fb0770015 100644
+--- a/src/main/java/net/minecraft/server/ChunkMap.java
++++ b/src/main/java/net/minecraft/server/ChunkMap.java
+@@ -17,6 +17,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+         chunk.world.timings.syncChunkLoadPostTimer.startTiming(); // Paper
+         lastChunkByPos = chunk; // Paper
+         Chunk chunk1 = (Chunk) super.put(i, chunk);
++        if (chunk1 == null) { // Paper - we should never be overwriting chunks
+         ChunkCoordIntPair chunkcoordintpair = new ChunkCoordIntPair(i);
+ 
+         for (int j = chunkcoordintpair.x - 1; j <= chunkcoordintpair.x + 1; ++j) {
+@@ -47,7 +48,11 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+                     chunk.setNeighborLoaded(x, z);
+                 }
+             }
++            // Paper start
++        } } else {
++            a.error("Overwrote existing chunk! (" + chunk.world.getWorld().getName() + ":" + chunk.locX+"," + chunk.locZ + ")", new IllegalStateException());
+         }
++        // Paper end
+         // Paper start - if this is a spare chunk (not part of any players view distance), go ahead and queue it for unload.
+         if (!((WorldServer)chunk.world).getPlayerChunkMap().isChunkInUse(chunk.locX, chunk.locZ)) {
+             if (chunk.world.paperConfig.delayChunkUnloadsBy > 0) {
+@@ -69,6 +74,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+ 
+     public Chunk a(long i) {
+         Chunk chunk = (Chunk) super.remove(i);
++        if (chunk != null) { // Paper - don't decrement if we didn't remove anything
+         ChunkCoordIntPair chunkcoordintpair = new ChunkCoordIntPair(i);
+ 
+         for (int j = chunkcoordintpair.x - 1; j <= chunkcoordintpair.x + 1; ++j) {
+@@ -84,6 +90,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
+         }
+ 
+         // Paper start
++        } // close if (chunk != null)
+         if (lastChunkByPos != null && i == lastChunkByPos.chunkKey) {
+             lastChunkByPos = null;
+         }
+-- 
+2.19.1
+