From 5fecba3db5c27e2e84a44844d31925520b6c2e2e Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Tue, 22 Mar 2016 00:33:47 -0400
Subject: [PATCH] Use a Shared Random for Entities

Reduces memory usage and provides ensures more randomness, Especially since a lot of garbage entity objects get created.

diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
index 3d739c4316..ec57b0ad8f 100644
--- a/src/main/java/net/minecraft/server/Entity.java
+++ b/src/main/java/net/minecraft/server/Entity.java
@@ -54,6 +54,20 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
 
     // CraftBukkit start
     private static final int CURRENT_LEVEL = 2;
+    // Paper start
+    public static Random SHARED_RANDOM = new Random() {
+        private boolean locked = false;
+        @Override
+        public synchronized void setSeed(long seed) {
+            if (locked) {
+                LogManager.getLogger().error("Ignoring setSeed on Entity.SHARED_RANDOM", new Throwable());
+            } else {
+                super.setSeed(seed);
+                locked = true;
+            }
+        }
+    };
+    // Paper end
     static boolean isLevelAtLeast(NBTTagCompound tag, int level) {
         return tag.hasKey("Bukkit.updateLevel") && tag.getInt("Bukkit.updateLevel") >= level;
     }
@@ -189,7 +203,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
         this.B = Vec3D.a;
         this.av = 1.0F;
         this.aw = 1.0F;
-        this.random = new Random();
+        this.random = SHARED_RANDOM; // Paper
         this.fireTicks = -this.getMaxFireTicks();
         this.justCreated = true;
         this.uniqueID = MathHelper.a(this.random);
-- 
2.21.0