--- ../src-base/minecraft/net/minecraft/server/management/PlayerManager.java
+++ ../src-work/minecraft/net/minecraft/server/management/PlayerManager.java
@@ -18,14 +18,19 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
+//CraftBukkit start
+import java.util.Collections;
+import java.util.Queue;
+// CraftBukkit end
+
 public class PlayerManager
 {
     private static final Logger field_152627_a = LogManager.getLogger();
     private final WorldServer theWorldServer;
     private final List players = new ArrayList();
     private final LongHashMap playerInstances = new LongHashMap();
-    private final List chunkWatcherWithPlayers = new ArrayList();
-    private final List playerInstanceList = new ArrayList();
+    private final Queue chunkWatcherWithPlayers = new java.util.concurrent.ConcurrentLinkedQueue(); // CraftBukkit ArrayList -> ConcurrentLinkedQueue
+    private final Queue playerInstanceList = new java.util.concurrent.ConcurrentLinkedQueue(); // CraftBukkit ArrayList -> ConcurrentLinkedQueue
     private int playerViewRadius;
     private long previousTotalWorldTime;
     private final int[][] xzDirectionsConst = new int[][] {{1, 0}, {0, 1}, { -1, 0}, {0, -1}};
@@ -37,6 +42,14 @@
         this.func_152622_a(p_i1176_1_.func_73046_m().getConfigurationManager().getViewDistance());
     }
 
+    // Cauldron start - vanilla compatibility
+    public PlayerManager(WorldServer p_i1176_1_, int viewDistance /* Spigot */)
+    {
+        this.theWorldServer = p_i1176_1_;
+        this.func_152622_a(viewDistance); // Spigot
+    }
+    // Cauldron end
+
     public WorldServer getWorldServer()
     {
         return this.theWorldServer;
@@ -51,27 +64,38 @@
         if (i - this.previousTotalWorldTime > 8000L)
         {
             this.previousTotalWorldTime = i;
+            // CraftBukkit start - Use iterator
+            java.util.Iterator iterator = this.playerInstanceList.iterator();
 
-            for (j = 0; j < this.playerInstanceList.size(); ++j)
+            while (iterator.hasNext())
             {
-                playerinstance = (PlayerManager.PlayerInstance)this.playerInstanceList.get(j);
+                playerinstance = (PlayerManager.PlayerInstance)iterator.next();
                 playerinstance.sendChunkUpdate();
                 playerinstance.processChunk();
             }
         }
         else
         {
-            for (j = 0; j < this.chunkWatcherWithPlayers.size(); ++j)
+            java.util.Iterator iterator = this.chunkWatcherWithPlayers.iterator();
+
+            while (iterator.hasNext())
             {
-                playerinstance = (PlayerManager.PlayerInstance)this.chunkWatcherWithPlayers.get(j);
+                playerinstance = (PlayerManager.PlayerInstance)iterator.next();
                 playerinstance.sendChunkUpdate();
+                iterator.remove();
+                // CraftBukkit end
             }
         }
 
-        this.chunkWatcherWithPlayers.clear();
+        // this.chunkWatcherWithPlayers.clear(); // CraftBukkit - Removals are already covered
 
         if (this.players.isEmpty())
         {
+            if (this.theWorldServer.loadedEntityList.size() == 0 || this.theWorldServer.theChunkProviderServer.loadedChunkHashMap_KC.size() == 0)
+            {
+                return; // CraftBukkit - Only do unload when we go from non-empty to empty
+            }
+
             WorldProvider worldprovider = this.theWorldServer.provider;
 
             if (!worldprovider.canRespawnHere())
@@ -102,6 +126,20 @@
         return playerinstance;
     }
 
+    // CraftBukkit start
+    public final boolean isChunkInUse(int x, int z)
+    {
+        PlayerManager.PlayerInstance pi = getOrCreateChunkWatcher(x, z, false);
+
+        if (pi != null)
+        {
+            return (pi.playersWatchingChunk.size() > 0);
+        }
+
+        return false;
+    }
+    // CraftBukkit end
+
     public void markBlockForUpdate(int p_151250_1_, int p_151250_2_, int p_151250_3_)
     {
         int l = p_151250_1_ >> 4;
@@ -541,7 +579,7 @@
                     {
                         i = this.chunkLocation.chunkXPos * 16;
                         j = this.chunkLocation.chunkZPos * 16;
-                        this.sendToAllPlayersWatchingChunk(new S21PacketChunkData(PlayerManager.this.theWorldServer.getChunkFromChunkCoords(this.chunkLocation.chunkXPos, this.chunkLocation.chunkZPos), false, this.flagsYAreasToUpdate));
+                        this.sendToAllPlayersWatchingChunk(new S21PacketChunkData(PlayerManager.this.theWorldServer.getChunkFromChunkCoords(this.chunkLocation.chunkXPos, this.chunkLocation.chunkZPos), (this.flagsYAreasToUpdate == 0xFFFF), this.flagsYAreasToUpdate)); // CraftBukkit - send everything (including biome) if all sections flagged
 
                         // Forge: Grabs ALL tile entities is costly on a modded server, only send needed ones
                         for (k = 0; false && k < 16; ++k)