Paper/Spigot-Server-Patches/0497-Fix-Non-Full-Status-Chunk-NBT-Memory-Leak.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 23 May 2020 01:31:06 -0400
Subject: [PATCH] Fix Non Full Status Chunk NBT Memory Leak

Any full status chunk that was requested for any status less than full
would hold onto their entire nbt tree and every variable in that function.

This was due to use of a lambda that persists on the Chunk object
until that chunk reaches FULL status.

With introduction of no tick, we greatly increased the number of non
full chunks so this was really starting to hurt.

We further improve it by making a copy of the nbt tag with only the memory
it needs, so that we dont have to hold a copy to the entire compound.

diff --git a/src/main/java/net/minecraft/server/ChunkRegionLoader.java b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
index 4b7c4643f04448aaccc66f26a9dea2323bea420d..ac58fcb7985ebe0cfdab6e1400deb37c233ff637 100644
--- a/src/main/java/net/minecraft/server/ChunkRegionLoader.java
+++ b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
@@ -156,9 +156,9 @@ public class ChunkRegionLoader {
                 object2 = protochunkticklist1;
             }
 
-            object = new Chunk(worldserver.getMinecraftWorld(), chunkcoordintpair, biomestorage, chunkconverter, (TickList) object1, (TickList) object2, j, achunksection, (chunk) -> {
-                loadEntities(nbttagcompound1, chunk);
-            });
+            object = new Chunk(worldserver.getMinecraftWorld(), chunkcoordintpair, biomestorage, chunkconverter, (TickList) object1, (TickList) object2, j, achunksection, // Paper start - fix massive nbt memory leak due to lambda. move lambda into a container method to not leak scope. Only clone needed NBT keys.
+                createLoadEntitiesConsumer(new SafeNBTCopy(nbttagcompound1, "TileEntities", "Entities"))
+            );// Paper end
         } else {
             ProtoChunk protochunk = new ProtoChunk(chunkcoordintpair, chunkconverter, achunksection, protochunkticklist, protochunkticklist1, worldserver); // Paper - Anti-Xray - Add parameter
 
@@ -264,6 +264,37 @@ public class ChunkRegionLoader {
             return new InProgressChunkHolder(protochunk1, tasksToExecuteOnMain); // Paper - Async chunk loading
         }
     }
+    // Paper start
+
+    /**
+     * This wrapper will error out if any key is accessed that wasn't copied so we can catch it easy on an update
+     */
+    private static class SafeNBTCopy extends NBTTagCompound {
+        private final java.util.Set<String> keys = new java.util.HashSet<String>();
+        public SafeNBTCopy(NBTTagCompound base, String... keys) {
+            for (String key : keys) {
+                this.keys.add(key);
+                this.set(key, base.get(key));
+            }
+        }
+
+        @Override
+        public boolean hasKey(String s) {
+            if (this.keys.contains(s)) {
+                return true;
+            }
+            throw new IllegalStateException("Missing Key " + s + " in SafeNBTCopy");
+        }
+
+        @Override
+        public boolean hasKeyOfType(String s, int i) {
+            return hasKey(s) && super.hasKeyOfType(s, i);
+        }
+    }
+    private static java.util.function.Consumer<Chunk> createLoadEntitiesConsumer(NBTTagCompound nbt) {
+        return (chunk) -> loadEntities(nbt, chunk);
+    }
+    // Paper end
 
     // Paper start - async chunk save for unload
     public static final class AsyncSaveData {