Paper/nms-patches/PlayerChunk.patch

--- a/net/minecraft/server/PlayerChunk.java
+++ b/net/minecraft/server/PlayerChunk.java
@@ -4,16 +4,18 @@
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.bukkit.craftbukkit.chunkio.ChunkIOExecutor;
 
 public class PlayerChunk {
 
     private static final Logger a = LogManager.getLogger();
     private final PlayerChunkMap playerChunkMap;
-    private final List<EntityPlayer> c = Lists.newArrayList();
+    public final List<EntityPlayer> c = Lists.newArrayList(); // CraftBukkit - public
     private final ChunkCoordIntPair location;
     private final short[] dirtyBlocks = new short[64];
     private Chunk chunk;
@@ -22,17 +24,28 @@
     private long i;
     private boolean done;
 
+    // CraftBukkit start - add fields
+    private final HashMap<EntityPlayer, Runnable> players = new HashMap<EntityPlayer, Runnable>();
+    private Runnable loadedRunnable = new Runnable() {
+        public void run() {
+            PlayerChunk.this.chunk = PlayerChunk.this.playerChunkMap.getWorld().getChunkProviderServer().getOrLoadChunkAt(location.x, location.z);
+        }
+    };
+    // CraftBukkit end
+
     public PlayerChunk(PlayerChunkMap playerchunkmap, int i, int j) {
         this.playerChunkMap = playerchunkmap;
         this.location = new ChunkCoordIntPair(i, j);
-        this.chunk = playerchunkmap.getWorld().getChunkProviderServer().getOrLoadChunkAt(i, j);
+        // CraftBukkit start
+        this.chunk = playerchunkmap.getWorld().getChunkProviderServer().getChunkAt(i, j, loadedRunnable);
+        // CraftBukkit end
     }
 
     public ChunkCoordIntPair a() {
         return this.location;
     }
 
-    public void a(EntityPlayer entityplayer) {
+    public void a(final EntityPlayer entityplayer) {  // CraftBukkit - added final to argument
         if (this.c.contains(entityplayer)) {
             PlayerChunk.a.debug("Failed to add player. {} already is in chunk {}, {}", new Object[] { entityplayer, Integer.valueOf(this.location.x), Integer.valueOf(this.location.z)});
         } else {
@@ -41,19 +54,50 @@
             }
 
             this.c.add(entityplayer);
+            // CraftBukkit start - use async chunk io
+            // if (this.j) {
+            //     this.sendChunk(entityplayer);
+            // }
+            Runnable playerRunnable;
             if (this.done) {
-                this.sendChunk(entityplayer);
+                playerRunnable = null;
+                sendChunk(entityplayer);
+            } else {
+                playerRunnable = new Runnable() {
+                    public void run() {
+                        sendChunk(entityplayer);
+                    }
+                };
+                playerChunkMap.getWorld().getChunkProviderServer().getChunkAt(this.location.x, this.location.z, playerRunnable);
             }
 
+            this.players.put(entityplayer, playerRunnable);
+            // CraftBukkit end
+
         }
     }
 
     public void b(EntityPlayer entityplayer) {
         if (this.c.contains(entityplayer)) {
+            // CraftBukkit start - If we haven't loaded yet don't load the chunk just so we can clean it up
+            if (!this.done) {
+                ChunkIOExecutor.dropQueuedChunkLoad(this.playerChunkMap.getWorld(), this.location.x, this.location.z, this.players.get(entityplayer));
+                this.c.remove(entityplayer);
+                this.players.remove(entityplayer);
+
+                if (this.c.isEmpty()) {
+                    ChunkIOExecutor.dropQueuedChunkLoad(this.playerChunkMap.getWorld(), this.location.x, this.location.z, this.loadedRunnable);
+                    this.playerChunkMap.b(this);
+                }
+
+                return;
+            }
+            // CraftBukkit end
             if (this.done) {
                 entityplayer.playerConnection.sendPacket(new PacketPlayOutUnloadChunk(this.location.x, this.location.z));
             }
 
+            this.players.remove(entityplayer); // CraftBukkit
             this.c.remove(entityplayer);
             if (this.c.isEmpty()) {
                 this.playerChunkMap.b(this);
@@ -63,8 +107,8 @@
     }
 
     public boolean a(boolean flag) {
-        if (this.chunk != null) {
-            return true;
+        if (this.chunk != null || true) { // CraftBukkit
+            return done; // CraftBukkit
         } else {
             if (flag) {
                 this.chunk = this.playerChunkMap.getWorld().getChunkProviderServer().getChunkAt(this.location.x, this.location.z);