SPIGOT-5228: Entities that are removed during chunk unloads are not

properly removed from the chunk.

This could lead to dead entities accumulating in memory over time if the
chunk never gets fully unloaded (as it is the case for chunks around the
spawn region).

The issue is that Minecraft processes the removal of these entities
during the next tick, when the chunk has already switched to state
INACCESSIBLE and can no longer be retrieved as usual.

For the purpose of removing dead entities from their still loaded but no
longer accessible chunk, this adds and uses a new method with which a
chunk can be accessed without checking its current state first.

By: blablubbabc <lukas@wirsindwir.de>

paper-server/nms-patches/ChunkProviderServer.patch

@@ -1,6 +1,6 @@
 --- a/net/minecraft/server/ChunkProviderServer.java
 +++ b/net/minecraft/server/ChunkProviderServer.java
-@@ -54,6 +54,16 @@
+@@ -54,6 +54,24 @@
          this.clearCache();
      }
  
@@ -12,12 +12,20 @@
 +        }
 +        return chunk.getFullChunk() != null;
 +    }
++
++    public Chunk getChunkUnchecked(int chunkX, int chunkZ) {
++        PlayerChunk chunk = this.playerChunkMap.getUpdatingChunk(ChunkCoordIntPair.pair(chunkX, chunkZ));
++        if (chunk == null) {
++            return null;
++        }
++        return chunk.getFullChunkUnchecked();
++    }
 +    // CraftBukkit end
 +
      @Override
      public LightEngineThreaded getLightEngine() {
          return this.lightEngine;
-@@ -98,7 +108,7 @@
+@@ -98,7 +116,7 @@
              for (int l = 0; l < 4; ++l) {
                  if (k == this.cachePos[l] && chunkstatus == this.cacheStatus[l]) {
                      ichunkaccess = this.cacheChunk[l];
@@ -26,7 +34,7 @@
                          return ichunkaccess;
                      }
                  }
-@@ -144,12 +154,12 @@
+@@ -144,12 +162,12 @@
              if (playerchunk == null) {
                  return null;
              } else {
@@ -41,7 +49,7 @@
  
                      if (ichunkaccess1 != null) {
                          this.a(k, ichunkaccess1, ChunkStatus.FULL);
-@@ -176,7 +186,15 @@
+@@ -176,7 +194,15 @@
          int l = 33 + ChunkStatus.a(chunkstatus);
          PlayerChunk playerchunk = this.getChunk(k);
  
@@ -58,7 +66,7 @@
              this.chunkMapDistance.a(TicketType.UNKNOWN, chunkcoordintpair, l, chunkcoordintpair);
              if (this.a(playerchunk, l)) {
                  GameProfilerFiller gameprofilerfiller = this.world.getMethodProfiler();
-@@ -195,7 +213,7 @@
+@@ -195,7 +221,7 @@
      }
  
      private boolean a(@Nullable PlayerChunk playerchunk, int i) {
@@ -67,7 +75,7 @@
      }
  
      public boolean isLoaded(int i, int j) {
-@@ -257,19 +275,19 @@
+@@ -257,19 +283,19 @@
      public boolean a(Entity entity) {
          long i = ChunkCoordIntPair.pair(MathHelper.floor(entity.locX()) >> 4, MathHelper.floor(entity.locZ()) >> 4);
  
@@ -90,7 +98,7 @@
      }
  
      private boolean a(long i, Function<PlayerChunk, CompletableFuture<Either<Chunk, PlayerChunk.Failure>>> function) {
-@@ -291,11 +309,31 @@
+@@ -291,11 +317,31 @@
  
      @Override
      public void close() throws IOException {
@@ -123,7 +131,7 @@
      public void tick(BooleanSupplier booleansupplier) {
          this.world.getMethodProfiler().enter("purge");
          this.chunkMapDistance.purgeTickets();
-@@ -315,12 +353,12 @@
+@@ -315,12 +361,12 @@
          this.lastTickTime = i;
          WorldData worlddata = this.world.getWorldData();
          boolean flag = this.world.isDebugWorld();
@@ -138,7 +146,7 @@
  
              this.world.getMethodProfiler().enter("naturalSpawnCount");
              int l = this.chunkMapDistance.b();
-@@ -507,12 +545,18 @@
+@@ -507,12 +553,18 @@
  
          @Override
          protected boolean executeNext() {

paper-server/nms-patches/PlayerChunk.patch

@@ -9,23 +9,27 @@
          this.dirtyBlocks = new ShortSet[16];
          this.location = chunkcoordintpair;
          this.lightEngine = lightengine;
-@@ -56,6 +56,15 @@
+@@ -56,6 +56,19 @@
          this.a(i);
      }
  
 +    // CraftBukkit start
 +    public Chunk getFullChunk() {
 +        if (!getChunkState(this.oldTicketLevel).isAtLeast(PlayerChunk.State.BORDER)) return null; // note: using oldTicketLevel for isLoaded checks
++        return this.getFullChunkUnchecked();
++    }
++
++    public Chunk getFullChunkUnchecked() {
 +        CompletableFuture<Either<IChunkAccess, PlayerChunk.Failure>> statusFuture = this.getStatusFutureUnchecked(ChunkStatus.FULL);
 +        Either<IChunkAccess, PlayerChunk.Failure> either = (Either<IChunkAccess, PlayerChunk.Failure>) statusFuture.getNow(null);
-+        return either == null ? null : (Chunk) either.left().orElse(null);
++        return (either == null) ? null : (Chunk) either.left().orElse(null);
 +    }
 +    // CraftBukkit end
 +
      public CompletableFuture<Either<IChunkAccess, PlayerChunk.Failure>> getStatusFutureUnchecked(ChunkStatus chunkstatus) {
          CompletableFuture<Either<IChunkAccess, PlayerChunk.Failure>> completablefuture = (CompletableFuture) this.statusFutures.get(chunkstatus.c());
  
-@@ -81,9 +90,9 @@
+@@ -81,9 +94,9 @@
      @Nullable
      public Chunk getChunk() {
          CompletableFuture<Either<Chunk, PlayerChunk.Failure>> completablefuture = this.a();
@@ -37,7 +41,7 @@
      }
  
      @Nullable
-@@ -114,6 +123,7 @@
+@@ -114,6 +127,7 @@
          if (chunk != null) {
              byte b0 = (byte) SectionPosition.a(blockposition.getY());
  
@@ -45,7 +49,7 @@
              if (this.dirtyBlocks[b0] == null) {
                  this.p = true;
                  this.dirtyBlocks[b0] = new ShortArraySet();
-@@ -216,7 +226,7 @@
+@@ -216,7 +230,7 @@
          CompletableFuture<Either<IChunkAccess, PlayerChunk.Failure>> completablefuture = (CompletableFuture) this.statusFutures.get(i);
  
          if (completablefuture != null) {
@@ -54,7 +58,7 @@
  
              if (either == null || either.left().isPresent()) {
                  return completablefuture;
-@@ -271,6 +281,30 @@
+@@ -271,6 +285,30 @@
          boolean flag1 = this.ticketLevel <= PlayerChunkMap.GOLDEN_TICKET;
          PlayerChunk.State playerchunk_state = getChunkState(this.oldTicketLevel);
          PlayerChunk.State playerchunk_state1 = getChunkState(this.ticketLevel);
@@ -85,7 +89,7 @@
          CompletableFuture completablefuture;
  
          if (flag) {
-@@ -302,7 +336,7 @@
+@@ -302,7 +340,7 @@
          if (flag2 && !flag3) {
              completablefuture = this.fullChunkFuture;
              this.fullChunkFuture = PlayerChunk.UNLOADED_CHUNK_FUTURE;
@@ -94,7 +98,7 @@
                  playerchunkmap.getClass();
                  return either1.ifLeft(playerchunkmap::a);
              }));
-@@ -340,6 +374,26 @@
+@@ -340,6 +378,26 @@
  
          this.u.a(this.location, this::k, this.ticketLevel, this::d);
          this.oldTicketLevel = this.ticketLevel;

paper-server/nms-patches/WorldServer.patch

@@ -448,6 +448,15 @@
          }
  
      }
+@@ -909,7 +1070,7 @@
+     }
+ 
+     private void removeEntityFromChunk(Entity entity) {
+-        IChunkAccess ichunkaccess = this.getChunkAt(entity.chunkX, entity.chunkZ, ChunkStatus.FULL, false);
++        IChunkAccess ichunkaccess = chunkProvider.getChunkUnchecked(entity.chunkX, entity.chunkZ); // CraftBukkit - SPIGOT-5228: getChunkAt won't find the entity's chunk if it has already been unloaded (i.e. if it switched to state INACCESSIBLE).
+ 
+         if (ichunkaccess instanceof Chunk) {
+             ((Chunk) ichunkaccess).b(entity);
 @@ -923,10 +1084,33 @@
          this.everyoneSleeping();
      }