PaperMC/patches/server/0070-Use-a-Shared-Random-for-Entities.patch

From 0000000000000000000000000000000000000000 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/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index e6917848029b1686e4e3a1a0eadac85eda92518d..3b998ca5230dc03a7faf2b0d1d1731b442337346 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -105,6 +105,7 @@ import net.minecraft.world.level.entity.EntityInLevelCallback;
 import net.minecraft.world.level.gameevent.DynamicGameEventListener;
 import net.minecraft.world.level.gameevent.GameEvent;
 import net.minecraft.world.level.levelgen.Heightmap;
+import net.minecraft.world.level.levelgen.PositionalRandomFactory;
 import net.minecraft.world.level.material.Fluid;
 import net.minecraft.world.level.material.FluidState;
 import net.minecraft.world.level.material.PushReaction;
@@ -158,6 +159,38 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
         return tag.contains("Bukkit.updateLevel") && tag.getInt("Bukkit.updateLevel") >= level;
     }
 
+    // Paper start
+    public static RandomSource SHARED_RANDOM = new RandomRandomSource();
+    private static final class RandomRandomSource extends java.util.Random implements RandomSource {
+        private boolean locked = false;
+
+        @Override
+        public synchronized void setSeed(long seed) {
+            if (locked) {
+                LOGGER.error("Ignoring setSeed on Entity.SHARED_RANDOM", new Throwable());
+            } else {
+                super.setSeed(seed);
+                locked = true;
+            }
+        }
+
+        @Override
+        public RandomSource fork() {
+            return new net.minecraft.world.level.levelgen.LegacyRandomSource(this.nextLong());
+        }
+
+        @Override
+        public PositionalRandomFactory forkPositional() {
+            return new net.minecraft.world.level.levelgen.LegacyRandomSource.LegacyPositionalRandomFactory(this.nextLong());
+        }
+
+        @Override
+        public int nextInt(int origin, int bound) {
+            return RandomSource.super.nextInt(origin, bound);
+        }
+    }
+    // Paper end
+
     private CraftEntity bukkitEntity;
 
     public CraftEntity getBukkitEntity() {
@@ -345,7 +378,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
         this.bb = Entity.INITIAL_AABB;
         this.stuckSpeedMultiplier = Vec3.ZERO;
         this.nextStep = 1.0F;
-        this.random = RandomSource.create();
+        this.random = SHARED_RANDOM; // Paper
         this.remainingFireTicks = -this.getFireImmuneTicks();
         this.fluidHeight = new Object2DoubleArrayMap(2);
         this.fluidOnEyes = new HashSet();
diff --git a/src/main/java/net/minecraft/world/entity/animal/Squid.java b/src/main/java/net/minecraft/world/entity/animal/Squid.java
index 8e63ab510e4c2e458da726ca67be4d3b5274e7b7..a51424d29ac353cf1bec4d1484db0acb63bebba5 100644
--- a/src/main/java/net/minecraft/world/entity/animal/Squid.java
+++ b/src/main/java/net/minecraft/world/entity/animal/Squid.java
@@ -46,7 +46,7 @@ public class Squid extends WaterAnimal {
 
     public Squid(EntityType<? extends Squid> type, Level world) {
         super(type, world);
-        this.random.setSeed((long) this.getId());
+        //this.random.setSeed((long) this.getId()); // Paper - we set the random to shared, do not clobber the seed
         this.tentacleSpeed = 1.0F / (this.random.nextFloat() + 1.0F) * 0.2F;
     }