Paper/nms-patches/ChunkProviderServer.patch

--- a/net/minecraft/server/ChunkProviderServer.java
+++ b/net/minecraft/server/ChunkProviderServer.java
@@ -20,6 +20,11 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
+// CraftBukkit start
+import org.bukkit.craftbukkit.chunkio.ChunkIOExecutor;
+import org.bukkit.event.world.ChunkUnloadEvent;
+// CraftBukkit end
+
 public class ChunkProviderServer implements IChunkProvider {
 
     private static final Logger a = LogManager.getLogger();
@@ -35,7 +40,7 @@
         this.world = worldserver;
         this.chunkLoader = ichunkloader;
         this.chunkGenerator = chunkgenerator;
-        this.f = new ChunkTaskScheduler(2, worldserver, chunkgenerator, ichunkloader, iasynctaskhandler);
+        this.f = new ChunkTaskScheduler(0, worldserver, chunkgenerator, ichunkloader, iasynctaskhandler); // CraftBukkit - very buggy, broken in lots of __subtle__ ways. Same goes for async chunk loading. Also Bukkit API / plugins can't handle async events at all anyway.
         this.g = new SchedulerBatch(this.f);
     }
 
@@ -77,9 +82,10 @@
     @Nullable
     private Chunk loadChunkAt(int i, int j) {
         try {
-            Chunk chunk = this.chunkLoader.a(this.world, i, j, (chunk) -> {
-                chunk.setLastSaved(this.world.getTime());
-                this.chunks.put(ChunkCoordIntPair.a(i, j), chunk);
+            // CraftBukkit - decompile error
+            Chunk chunk = this.chunkLoader.a(this.world, i, j, (chunk1) -> {
+                chunk1.setLastSaved(this.world.getTime());
+                this.chunks.put(ChunkCoordIntPair.a(i, j), chunk1);
             });
 
             if (chunk != null) {
@@ -104,6 +110,12 @@
         }
     }
 
+    // CraftBukkit start
+    public Chunk getChunkIfLoaded(int x, int z) {
+        return chunks.get(ChunkCoordIntPair.a(x, z));
+    }
+    // CraftBukkit end
+
     public Chunk getChunkAt(int i, int j) {
         Chunk chunk = this.getOrLoadChunkAt(i, j);
 
@@ -125,7 +137,7 @@
         synchronized (this.chunks) {
             IChunkAccess ichunkaccess = (IChunkAccess) this.chunks.get(ChunkCoordIntPair.a(i, j));
 
-            return ichunkaccess != null ? ichunkaccess : (IChunkAccess) this.f.c((Object) (new ChunkCoordIntPair(i, j)));
+            return ichunkaccess != null ? ichunkaccess : (IChunkAccess) this.f.c((new ChunkCoordIntPair(i, j))); // CraftBukkit - decompile error
         }
     }
 
@@ -150,7 +162,7 @@
     public CompletableFuture<Chunk> generateChunk(int i, int j) {
         this.g.b();
         this.g.a(new ChunkCoordIntPair(i, j));
-        CompletableFuture completablefuture = this.g.c();
+        CompletableFuture<ProtoChunk> completablefuture = this.g.c(); // CraftBukkit - decompile error
 
         return completablefuture.thenApply(this::a);
     }
@@ -268,10 +280,12 @@
                     Chunk chunk = (Chunk) this.chunks.get(olong);
 
                     if (chunk != null && chunk.d) {
-                        chunk.removeEntities();
-                        this.saveChunk(chunk);
-                        this.saveChunkNOP(chunk);
-                        this.chunks.remove(olong);
+                        // CraftBukkit start - move unload logic to own method
+                        if (!unloadChunk(chunk, true)) {
+                            continue;
+                        }
+                        // CraftBukkit end
+
                         ++i;
                     }
                 }
@@ -284,6 +298,40 @@
         return false;
     }
 
+    // CraftBukkit start
+    public boolean unloadChunk(Chunk chunk, boolean save) {
+        ChunkUnloadEvent event = new ChunkUnloadEvent(chunk.bukkitChunk, save);
+        this.world.getServer().getPluginManager().callEvent(event);
+        if (event.isCancelled()) {
+            return false;
+        }
+        save = event.isSaveChunk();
+
+        // Update neighbor counts
+        for (int x = -2; x < 3; x++) {
+            for (int z = -2; z < 3; z++) {
+                if (x == 0 && z == 0) {
+                    continue;
+                }
+
+                Chunk neighbor = this.getChunkIfLoaded(chunk.locX + x, chunk.locZ + z);
+                if (neighbor != null) {
+                    neighbor.setNeighborUnloaded(-x, -z);
+                    chunk.setNeighborUnloaded(x, z);
+                }
+            }
+        }
+        // Moved from unloadChunks above
+        chunk.removeEntities();
+        if (save) {
+            this.saveChunk(chunk);
+            this.saveChunkNOP(chunk);
+        }
+        this.chunks.remove(chunk.chunkKey);
+        return true;
+    }
+    // CraftBukkit end
+
     public boolean e() {
         return !this.world.savingDisabled;
     }