From 45425317236f1d52c740a0794657806b26af6247 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Tue, 8 Mar 2016 19:13:54 -0500
Subject: [PATCH] Optimize Navigation Listener

Replace WeakHashMap with an ArrayList and manually manage object
lifecycle. Gives superior iteration performance at a slight cost
to removal performance and also ensures entities are removed immediately
upon losing their validity within the world.

Additionally, change listener registration to be done upon world add
instead of immediate up creation. This provides benefit of only
registering and ticking real Navigation objects, and not invalid
entities (cancelled entity spawns for example).

diff --git a/src/main/java/net/minecraft/server/NavigationAbstract.java b/src/main/java/net/minecraft/server/NavigationAbstract.java
index 2f4265a..7cfe0af 100644
--- a/src/main/java/net/minecraft/server/NavigationAbstract.java
+++ b/src/main/java/net/minecraft/server/NavigationAbstract.java
@@ -32,7 +32,7 @@ public abstract class NavigationAbstract {
         this.b = world;
         this.g = entityinsentient.getAttributeInstance(GenericAttributes.FOLLOW_RANGE);
         this.s = this.a();
-        this.b.C().a(this);
+        //this.b.C().a(this); // Spigot - Optimized Nav Listener - registered on world add
     }
 
     protected abstract Pathfinder a();
diff --git a/src/main/java/net/minecraft/server/NavigationListener.java b/src/main/java/net/minecraft/server/NavigationListener.java
index f82ea80..ed79b03 100644
--- a/src/main/java/net/minecraft/server/NavigationListener.java
+++ b/src/main/java/net/minecraft/server/NavigationListener.java
@@ -1,26 +1,35 @@
 package net.minecraft.server;
 
+import java.util.ArrayList; // Spigot
+import java.util.List; // Spigot
 import java.util.WeakHashMap;
 
 public class NavigationListener implements IWorldAccess {
 
     private static final Object a = new Object();
-    private final WeakHashMap<NavigationAbstract, Object> b = new WeakHashMap();
+    private final List<NavigationAbstract> navigators = new ArrayList<NavigationAbstract>(); // Spigot
 
     public NavigationListener() {}
 
     public void a(NavigationAbstract navigationabstract) {
-        this.b.put(navigationabstract, NavigationListener.a);
+        //this.b.put(navigationabstract, NavigationListener.a); // Spigot
+        new Throwable("Unexpected NavigationListener add").printStackTrace(); // Spigot
     }
 
     public void a(World world, BlockPosition blockposition, IBlockData iblockdata, IBlockData iblockdata1, int i) {
         if (this.a(world, blockposition, iblockdata, iblockdata1)) {
+            /* // Spigot start
             NavigationAbstract[] anavigationabstract = (NavigationAbstract[]) this.b.keySet().toArray(new NavigationAbstract[0]);
             NavigationAbstract[] anavigationabstract1 = anavigationabstract;
             int j = anavigationabstract.length;
 
-            for (int k = 0; k < j; ++k) {
-                NavigationAbstract navigationabstract = anavigationabstract1[k];
+            */
+            // DO NOT USE AN ITERATOR! This must be a for (;;) to avoid CME.
+            // This is perfectly safe, as additions are ok to be done in this iteration
+            // and Removals are queued instead of immediate.
+            for (int k = 0; k < this.navigators.size(); ++k) {
+                NavigationAbstract navigationabstract = this.navigators.get(k);
+                // Spigot end
 
                 if (navigationabstract != null && !navigationabstract.i()) {
                     PathEntity pathentity = navigationabstract.k();
@@ -55,9 +64,21 @@ public class NavigationListener implements IWorldAccess {
 
     public void a(int i, boolean flag, double d0, double d1, double d2, double d3, double d4, double d5, int... aint) {}
 
-    public void a(Entity entity) {}
+    public void a(Entity entity) {
+        // Spigot start
+        if (entity instanceof EntityInsentient) {
+            this.navigators.add(((EntityInsentient) entity).navigation);
+        }
+        // Spigot end
+    }
 
-    public void b(Entity entity) {}
+    public void b(Entity entity) {
+        // Spigot start
+        if (entity instanceof EntityInsentient) {
+            this.navigators.remove(((EntityInsentient) entity).navigation);
+        }
+        // Spigot end
+    }
 
     public void a(SoundEffect soundeffect, BlockPosition blockposition) {}
 
-- 
2.5.0