Paper/nms-patches/ChunkProviderServer.patch

--- a/net/minecraft/server/ChunkProviderServer.java
+++ b/net/minecraft/server/ChunkProviderServer.java
@@ -241,6 +241,17 @@
         this.playerChunkMap.close();
     }
 
+    // CraftBukkit start - modelled on below
+    public void purgeUnload() {
+        this.world.getMethodProfiler().enter("purge");
+        this.chunkMapDistance.purgeTickets();
+        this.tickDistanceManager();
+        this.world.getMethodProfiler().exitEnter("unload");
+        this.playerChunkMap.unloadChunks(() -> true);
+        this.world.getMethodProfiler().exit();
+    }
+    // CraftBukkit end
+
     public void tick(BooleanSupplier booleansupplier) {
         this.world.getMethodProfiler().enter("purge");
         this.chunkMapDistance.purgeTickets();
@@ -260,13 +271,13 @@
         this.lastTickTime = i;
         WorldData worlddata = this.world.getWorldData();
         boolean flag = worlddata.getType() == WorldType.DEBUG_ALL_BLOCK_STATES;
-        boolean flag1 = this.world.getGameRules().getBoolean("doMobSpawning");
+        boolean flag1 = this.world.getGameRules().getBoolean("doMobSpawning") && !world.getPlayers().isEmpty(); // CraftBukkit
 
         if (!flag) {
             this.world.getMethodProfiler().enter("pollingChunks");
             int k = this.world.getGameRules().c("randomTickSpeed");
             BlockPosition blockposition = this.world.getSpawn();
-            boolean flag2 = worlddata.getTime() % 400L == 0L;
+            boolean flag2 = world.ticksPerAnimalSpawns != 0L && worlddata.getTime() % world.ticksPerAnimalSpawns == 0L; // CraftBukkit // PAIL: TODO monster ticks
 
             this.world.getMethodProfiler().enter("naturalSpawnCount");
             int l = this.chunkMapDistance.b();
@@ -299,8 +310,30 @@
                             for (int j1 = 0; j1 < i1; ++j1) {
                                 EnumCreatureType enumcreaturetype = aenumcreaturetype1[j1];
 
+                                // CraftBukkit start - Use per-world spawn limits
+                                int limit = enumcreaturetype.b();
+                                switch (enumcreaturetype) {
+                                    case MONSTER:
+                                        limit = world.getWorld().getMonsterSpawnLimit();
+                                        break;
+                                    case CREATURE:
+                                        limit = world.getWorld().getAnimalSpawnLimit();
+                                        break;
+                                    case WATER_CREATURE:
+                                        limit = world.getWorld().getWaterAnimalSpawnLimit();
+                                        break;
+                                    case AMBIENT:
+                                        limit = world.getWorld().getAmbientSpawnLimit();
+                                        break;
+                                }
+
+                                if (limit == 0) {
+                                    continue;
+                                }
+                                // CraftBukkit end
+
                                 if (enumcreaturetype != EnumCreatureType.MISC && (!enumcreaturetype.c() || this.allowAnimals) && (enumcreaturetype.c() || this.allowMonsters) && (!enumcreaturetype.d() || flag2)) {
-                                    int k1 = enumcreaturetype.b() * l / ChunkProviderServer.b;
+                                    int k1 = limit * l / ChunkProviderServer.b; // CraftBukkit - use per-world limits
 
                                     if (object2intmap.getInt(enumcreaturetype) <= k1) {
                                         SpawnerCreature.a(enumcreaturetype, (World) this.world, chunk, blockposition);