From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: jmp <jasonpenilla2@me.com>
Date: Wed, 18 Nov 2020 20:52:25 -0800
Subject: [PATCH] Entity load/save limit per chunk

Adds a config option to limit the number of entities saved and loaded
to a chunk. The default values of -1 disable the limit. Although
defaults are only included for certain entites, this allows setting
limits for any entity type.

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index c5495e02c3fe271b26f62ea2ec64e07957edf37e..234d2daecc5d0bf6a99c0a5f4a87f947a15029d9 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -11,6 +11,7 @@ import com.destroystokyo.paper.antixray.ChunkPacketBlockControllerAntiXray.Engin
 import net.minecraft.server.EntityVindicator;
 import net.minecraft.server.EntityZombie;
 import net.minecraft.server.EnumDifficulty;
+import net.minecraft.server.EntityTypes;
 import org.bukkit.Bukkit;
 import org.bukkit.Material;
 import org.bukkit.configuration.ConfigurationSection;
@@ -761,4 +762,18 @@ public class PaperWorldConfig {
             EnumDifficulty.class
         );
     }
+
+    public Map<EntityTypes<?>, Integer> entityPerChunkSaveLimits = new HashMap<>();
+    private void entityPerChunkSaveLimits() {
+        getInt("entity-per-chunk-save-limit.experience_orb", -1);
+        getInt("entity-per-chunk-save-limit.snowball", -1);
+        getInt("entity-per-chunk-save-limit.ender_pearl", -1);
+        getInt("entity-per-chunk-save-limit.arrow", -1);
+        EntityTypes.getEntityNameList().forEach(name -> {
+            final EntityTypes<?> type = EntityTypes.getByName(name.getKey()).orElseThrow(() -> new IllegalStateException("Unknown Entity Type: " + name.toString()));
+            final String path = ".entity-per-chunk-save-limit." + name.getKey();
+            final int value = config.getInt("world-settings." + worldName + path, config.getInt("world-settings.default" + path, -1)); // get without setting defaults
+            if (value != -1) entityPerChunkSaveLimits.put(type, value);
+        });
+    }
 }
diff --git a/src/main/java/net/minecraft/server/ChunkRegionLoader.java b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
index 8e7da2c5f3852920ec5fbcdd2bff4d299e6aa499..060ef42bc8f22688071fa375bd4dbab8dd2c1e9e 100644
--- a/src/main/java/net/minecraft/server/ChunkRegionLoader.java
+++ b/src/main/java/net/minecraft/server/ChunkRegionLoader.java
@@ -495,11 +495,22 @@ public class ChunkRegionLoader {
 
             chunk.d(false);
 
+            // Paper start
+            final Map<EntityTypes<?>, Integer> savedEntityCounts = Maps.newHashMap();
             for (int j = 0; j < chunk.getEntitySlices().length; ++j) {
                 Iterator iterator1 = chunk.getEntitySlices()[j].iterator();
 
                 while (iterator1.hasNext()) {
                     Entity entity = (Entity) iterator1.next();
+                    final EntityTypes<?> entityType = entity.getEntityType();
+                    final int saveLimit = worldserver.paperConfig.entityPerChunkSaveLimits.getOrDefault(entityType, -1);
+                    if (saveLimit > -1) {
+                        if (savedEntityCounts.getOrDefault(entityType, 0) >= saveLimit) {
+                            continue;
+                        }
+                        savedEntityCounts.merge(entityType, 1, Integer::sum);
+                    }
+                    // Paper end
                     NBTTagCompound nbttagcompound4 = new NBTTagCompound();
                     // Paper start
                     if (asyncsavedata == null && !entity.dead && (int) Math.floor(entity.locX()) >> 4 != chunk.getPos().x || (int) Math.floor(entity.locZ()) >> 4 != chunk.getPos().z) {
@@ -630,10 +641,21 @@ public class ChunkRegionLoader {
         NBTTagList nbttaglist = nbttagcompound.getList("Entities", 10);
         World world = chunk.getWorld();
 
+        // Paper start
+        final Map<EntityTypes<?>, Integer> loadedEntityCounts = Maps.newHashMap();
         for (int i = 0; i < nbttaglist.size(); ++i) {
             NBTTagCompound nbttagcompound1 = nbttaglist.getCompound(i);
 
             EntityTypes.a(nbttagcompound1, world, (entity) -> {
+                final EntityTypes<?> entityType = entity.getEntityType();
+                final int saveLimit = world.paperConfig.entityPerChunkSaveLimits.getOrDefault(entityType, -1);
+                if (saveLimit > -1) {
+                    if (loadedEntityCounts.getOrDefault(entityType, 0) >= saveLimit) {
+                        return entity;
+                    }
+                    loadedEntityCounts.merge(entityType, 1, Integer::sum);
+                }
+                // Paper end
                 chunk.a(entity);
                 return entity;
             });