Paper/Spigot-Server-Patches/0396-implement-optional-per-player-mob-spawns.patch

From 286402aba0b28823b89468bffb9e650c76311313 Mon Sep 17 00:00:00 2001
From: kickash32 <kickash32@gmail.com>
Date: Mon, 19 Aug 2019 01:27:58 +0500
Subject: [PATCH] implement optional per player mob spawns


diff --git a/src/main/java/co/aikar/timings/WorldTimingsHandler.java b/src/main/java/co/aikar/timings/WorldTimingsHandler.java
index 98acbfa44d..a94ebf7c76 100644
--- a/src/main/java/co/aikar/timings/WorldTimingsHandler.java
+++ b/src/main/java/co/aikar/timings/WorldTimingsHandler.java
@@ -56,6 +56,7 @@ public class WorldTimingsHandler {
 
 
     public final Timing miscMobSpawning;
+    public final Timing playerMobDistanceMapUpdate;
 
     public final Timing poiUnload;
     public final Timing chunkUnload;
@@ -121,6 +122,7 @@ public class WorldTimingsHandler {
 
 
         miscMobSpawning = Timings.ofSafe(name + "Mob spawning - Misc");
+        playerMobDistanceMapUpdate = Timings.ofSafe(name + "Per Player Mob Spawning - Distance Map Update");
 
         poiUnload = Timings.ofSafe(name + "Chunk unload - POI");
         chunkUnload = Timings.ofSafe(name + "Chunk unload - Chunk");
diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 9d9260ad07..fd3dbea628 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -613,4 +613,9 @@ public class PaperWorldConfig {
             }
         }
     }
+
+    public boolean perPlayerMobSpawns = false;
+    private void perPlayerMobSpawns() {
+        perPlayerMobSpawns = getBoolean("per-player-mob-spawns", false);
+    }
 }
diff --git a/src/main/java/com/destroystokyo/paper/util/PlayerMobDistanceMap.java b/src/main/java/com/destroystokyo/paper/util/PlayerMobDistanceMap.java
new file mode 100644
index 0000000000..9ebd7ecb7a
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/util/PlayerMobDistanceMap.java
@@ -0,0 +1,253 @@
+package com.destroystokyo.paper.util;
+
+import it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ObjectLinkedOpenHashSet;
+import net.minecraft.server.ChunkCoordIntPair;
+import net.minecraft.server.EntityPlayer;
+import net.minecraft.server.SectionPosition;
+import org.spigotmc.AsyncCatcher;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/** @author Spottedleaf */
+public final class PlayerMobDistanceMap {
+
+    private static final PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> EMPTY_SET = new PooledHashSets.PooledObjectLinkedOpenHashSet<>();
+
+    private final Map<EntityPlayer, SectionPosition> players = new HashMap<>();
+    // we use linked for better iteration.
+    private final Long2ObjectOpenHashMap<PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer>> playerMap = new Long2ObjectOpenHashMap<>(32, 0.5f);
+    private int viewDistance;
+
+    private final PooledHashSets<EntityPlayer> pooledHashSets = new PooledHashSets<>();
+
+    public PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> getPlayersInRange(final ChunkCoordIntPair chunkPos) {
+        return this.getPlayersInRange(chunkPos.x, chunkPos.z);
+    }
+
+    public PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> getPlayersInRange(final int chunkX, final int chunkZ) {
+        return this.playerMap.getOrDefault(ChunkCoordIntPair.pair(chunkX, chunkZ), EMPTY_SET);
+    }
+
+    public void update(final List<EntityPlayer> currentPlayers, final int newViewDistance) {
+        AsyncCatcher.catchOp("Distance map update");
+        final ObjectLinkedOpenHashSet<EntityPlayer> gone = new ObjectLinkedOpenHashSet<>(this.players.keySet());
+
+        final int oldViewDistance = this.viewDistance;
+        this.viewDistance = newViewDistance;
+
+        for (final EntityPlayer player : currentPlayers) {
+            if (player.isSpectator() || !player.affectsSpawning) {
+                continue; // will be left in 'gone' (or not added at all)
+            }
+
+            gone.remove(player);
+
+            final SectionPosition newPosition = player.getPlayerMapSection();
+            final SectionPosition oldPosition = this.players.put(player, newPosition);
+
+            if (oldPosition == null) {
+                this.addNewPlayer(player, newPosition, newViewDistance);
+            } else {
+                this.updatePlayer(player, oldPosition, newPosition, oldViewDistance, newViewDistance);
+            }
+            //this.validatePlayer(player, newViewDistance); // debug only
+        }
+
+        for (final EntityPlayer player : gone) {
+            final SectionPosition oldPosition = this.players.remove(player);
+            if (oldPosition != null) {
+                this.removePlayer(player, oldPosition, oldViewDistance);
+            }
+        }
+    }
+
+    // expensive op, only for debug
+    private void validatePlayer(final EntityPlayer player, final int viewDistance) {
+        int entiesGot = 0;
+        int expectedEntries = (2 * viewDistance + 1);
+        expectedEntries *= expectedEntries;
+
+        final SectionPosition currPosition = player.getPlayerMapSection();
+
+        final int centerX = currPosition.getX();
+        final int centerZ = currPosition.getZ();
+
+        for (final Long2ObjectLinkedOpenHashMap.Entry<PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer>> entry : this.playerMap.long2ObjectEntrySet()) {
+            final long key = entry.getLongKey();
+            final PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> map = entry.getValue();
+
+            if (map.referenceCount == 0) {
+                throw new IllegalStateException("Invalid map");
+            }
+
+            if (map.set.contains(player)) {
+                ++entiesGot;
+
+                final int chunkX = ChunkCoordIntPair.getX(key);
+                final int chunkZ = ChunkCoordIntPair.getZ(key);
+
+                final int dist = Math.max(Math.abs(chunkX - centerX), Math.abs(chunkZ - centerZ));
+
+                if (dist > viewDistance) {
+                    throw new IllegalStateException("Expected view distance " + viewDistance + ", got " + dist);
+                }
+            }
+        }
+
+        if (entiesGot != expectedEntries) {
+            throw new IllegalStateException("Expected " + expectedEntries + ", got " + entiesGot);
+        }
+    }
+
+    private void addPlayerTo(final EntityPlayer player, final int chunkX, final int chunkZ) {
+       this.playerMap.compute(ChunkCoordIntPair.pair(chunkX, chunkZ), (final Long key, final PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> players) -> {
+           if (players == null) {
+               return player.cachedSingleMobDistanceMap;
+           } else {
+               return PlayerMobDistanceMap.this.pooledHashSets.findMapWith(players, player);
+           }
+        });
+    }
+
+    private void removePlayerFrom(final EntityPlayer player, final int chunkX, final int chunkZ) {
+        this.playerMap.compute(ChunkCoordIntPair.pair(chunkX, chunkZ), (final Long keyInMap, final PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> players) -> {
+            return PlayerMobDistanceMap.this.pooledHashSets.findMapWithout(players, player); // rets null instead of an empty map
+        });
+    }
+
+    private void updatePlayer(final EntityPlayer player, final SectionPosition oldPosition, final SectionPosition newPosition, final int oldViewDistance, final int newViewDistance) {
+        final int toX = newPosition.getX();
+        final int toZ = newPosition.getZ();
+        final int fromX = oldPosition.getX();
+        final int fromZ = oldPosition.getZ();
+
+        final int dx = toX - fromX;
+        final int dz = toZ - fromZ;
+
+        final int totalX = Math.abs(fromX - toX);
+        final int totalZ = Math.abs(fromZ - toZ);
+
+        if (Math.max(totalX, totalZ) > (2 * oldViewDistance)) {
+            // teleported?
+            this.removePlayer(player, oldPosition, oldViewDistance);
+            this.addNewPlayer(player, newPosition, newViewDistance);
+            return;
+        }
+
+        // x axis is width
+        // z axis is height
+        // right refers to the x axis of where we moved
+        // top refers to the z axis of where we moved
+
+        if (oldViewDistance == newViewDistance) {
+            // same view distance
+
+            // used for relative positioning
+            final int up = 1 | (dz >> (Integer.SIZE - 1)); // 1 if dz >= 0, -1 otherwise
+            final int right = 1 | (dx >> (Integer.SIZE - 1)); // 1 if dx >= 0, -1 otherwise
+
+            // The area excluded by overlapping the two view distance squares creates four rectangles:
+            // Two on the left, and two on the right. The ones on the left we consider the "removed" section
+            // and on the right the "added" section.
+            // https://i.imgur.com/MrnOBgI.png is a reference image. Note that the outside border is not actually
+            // exclusive to the regions they surround.
+
+            // 4 points of the rectangle
+            int maxX; // exclusive
+            int minX; // inclusive
+            int maxZ; // exclusive
+            int minZ; // inclusive
+
+            if (dx != 0) {
+                // handle right addition
+
+                maxX = toX + (oldViewDistance * right) + right; // exclusive
+                minX = fromX + (oldViewDistance * right) + right; // inclusive
+                maxZ = fromZ + (oldViewDistance * up) + up; // exclusive
+                minZ = toZ - (oldViewDistance * up); // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.addPlayerTo(player, currX, currZ);
+                    }
+                }
+            }
+
+            if (dz != 0) {
+                // handle up addition
+
+                maxX = toX + (oldViewDistance * right) + right; // exclusive
+                minX = toX - (oldViewDistance * right); // inclusive
+                maxZ = toZ + (oldViewDistance * up) + up; // exclusive
+                minZ = fromZ + (oldViewDistance * up) + up; // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.addPlayerTo(player, currX, currZ);
+                    }
+                }
+            }
+
+            if (dx != 0) {
+                // handle left removal
+
+                maxX = toX - (oldViewDistance * right); // exclusive
+                minX = fromX - (oldViewDistance * right); // inclusive
+                maxZ = fromZ + (oldViewDistance * up) + up; // exclusive
+                minZ = toZ - (oldViewDistance * up); // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.removePlayerFrom(player, currX, currZ);
+                    }
+                }
+            }
+
+            if (dz != 0) {
+                // handle down removal
+
+                maxX = fromX + (oldViewDistance * right) + right; // exclusive
+                minX = fromX - (oldViewDistance * right); // inclusive
+                maxZ = toZ - (oldViewDistance * up); // exclusive
+                minZ = fromZ - (oldViewDistance * up); // inclusive
+
+                for (int currX = minX; currX != maxX; currX += right) {
+                    for (int currZ = minZ; currZ != maxZ; currZ += up) {
+                        this.removePlayerFrom(player, currX, currZ);
+                    }
+                }
+            }
+        } else {
+            // different view distance
+            // for now :)
+            this.removePlayer(player, oldPosition, oldViewDistance);
+            this.addNewPlayer(player, newPosition, newViewDistance);
+        }
+    }
+
+    private void removePlayer(final EntityPlayer player, final SectionPosition position, final int viewDistance) {
+        final int x = position.getX();
+        final int z = position.getZ();
+
+        for (int xoff = -viewDistance; xoff <= viewDistance; ++xoff) {
+            for (int zoff = -viewDistance; zoff <= viewDistance; ++zoff) {
+                this.removePlayerFrom(player, x + xoff, z + zoff);
+            }
+        }
+    }
+
+    private void addNewPlayer(final EntityPlayer player, final SectionPosition position, final int viewDistance) {
+        final int x = position.getX();
+        final int z = position.getZ();
+
+        for (int xoff = -viewDistance; xoff <= viewDistance; ++xoff) {
+            for (int zoff = -viewDistance; zoff <= viewDistance; ++zoff) {
+                this.addPlayerTo(player, x + xoff, z + zoff);
+            }
+        }
+    }
+}
diff --git a/src/main/java/com/destroystokyo/paper/util/PooledHashSets.java b/src/main/java/com/destroystokyo/paper/util/PooledHashSets.java
new file mode 100644
index 0000000000..4f13d3ff83
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/util/PooledHashSets.java
@@ -0,0 +1,241 @@
+package com.destroystokyo.paper.util;
+
+import it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ObjectLinkedOpenHashSet;
+import java.lang.ref.WeakReference;
+import java.util.Iterator;
+
+/** @author Spottedleaf */
+public class PooledHashSets<E> {
+
+    // we really want to avoid that equals() check as much as possible...
+    protected final Object2ObjectOpenHashMap<PooledObjectLinkedOpenHashSet<E>, PooledObjectLinkedOpenHashSet<E>> mapPool = new Object2ObjectOpenHashMap<>(64, 0.25f);
+
+    protected void decrementReferenceCount(final PooledObjectLinkedOpenHashSet<E> current) {
+        if (current.referenceCount == 0) {
+            throw new IllegalStateException("Cannot decrement reference count for " + current);
+        }
+        if (current.referenceCount == -1 || --current.referenceCount > 0) {
+            return;
+        }
+
+        this.mapPool.remove(current);
+        return;
+    }
+
+    public PooledObjectLinkedOpenHashSet<E> findMapWith(final PooledObjectLinkedOpenHashSet<E> current, final E object) {
+        final PooledObjectLinkedOpenHashSet<E> cached = current.getAddCache(object);
+
+        if (cached != null) {
+            if (cached.referenceCount != -1) {
+                ++cached.referenceCount;
+            }
+
+            decrementReferenceCount(current);
+
+            return cached;
+        }
+
+        if (!current.add(object)) {
+            return current;
+        }
+
+        // we use get/put since we use a different key on put
+        PooledObjectLinkedOpenHashSet<E> ret = this.mapPool.get(current);
+
+        if (ret == null) {
+            ret = new PooledObjectLinkedOpenHashSet<>(current);
+            current.remove(object);
+            this.mapPool.put(ret, ret);
+            ret.referenceCount = 1;
+        } else {
+            if (ret.referenceCount != -1) {
+                ++ret.referenceCount;
+            }
+            current.remove(object);
+        }
+
+        current.updateAddCache(object, ret);
+
+        decrementReferenceCount(current);
+        return ret;
+    }
+
+    // rets null if current.size() == 1
+    public PooledObjectLinkedOpenHashSet<E> findMapWithout(final PooledObjectLinkedOpenHashSet<E> current, final E object) {
+        if (current.set.size() == 1) {
+            decrementReferenceCount(current);
+            return null;
+        }
+
+        final PooledObjectLinkedOpenHashSet<E> cached = current.getRemoveCache(object);
+
+        if (cached != null) {
+            if (cached.referenceCount != -1) {
+                ++cached.referenceCount;
+            }
+
+            decrementReferenceCount(current);
+
+            return cached;
+        }
+
+        if (!current.remove(object)) {
+            return current;
+        }
+
+        // we use get/put since we use a different key on put
+        PooledObjectLinkedOpenHashSet<E> ret = this.mapPool.get(current);
+
+        if (ret == null) {
+            ret = new PooledObjectLinkedOpenHashSet<>(current);
+            current.add(object);
+            this.mapPool.put(ret, ret);
+            ret.referenceCount = 1;
+        } else {
+            if (ret.referenceCount != -1) {
+                ++ret.referenceCount;
+            }
+            current.add(object);
+        }
+
+        current.updateRemoveCache(object, ret);
+
+        decrementReferenceCount(current);
+        return ret;
+    }
+
+    public static final class PooledObjectLinkedOpenHashSet<E> implements Iterable<E> {
+
+        private static final WeakReference NULL_REFERENCE = new WeakReference(null);
+
+        final ObjectLinkedOpenHashSet<E> set;
+        int referenceCount; // -1 if special
+        int hash; // optimize hashcode
+
+        // add cache
+        WeakReference<E> lastAddObject = NULL_REFERENCE;
+        WeakReference<PooledObjectLinkedOpenHashSet<E>> lastAddMap = NULL_REFERENCE;
+
+        // remove cache
+        WeakReference<E> lastRemoveObject = NULL_REFERENCE;
+        WeakReference<PooledObjectLinkedOpenHashSet<E>> lastRemoveMap = NULL_REFERENCE;
+
+        public PooledObjectLinkedOpenHashSet() {
+            this.set = new ObjectLinkedOpenHashSet<>(2, 0.6f);
+        }
+
+        public PooledObjectLinkedOpenHashSet(final E single) {
+            this();
+            this.referenceCount = -1;
+            this.add(single);
+        }
+
+        public PooledObjectLinkedOpenHashSet(final PooledObjectLinkedOpenHashSet<E> other) {
+            this.set = other.set.clone();
+            this.hash = other.hash;
+        }
+
+        // from https://github.com/Spottedleaf/ConcurrentUtil/blob/master/src/main/java/ca/spottedleaf/concurrentutil/util/IntegerUtil.java
+        // generated by https://github.com/skeeto/hash-prospector
+        static int hash0(int x) {
+            x *= 0x36935555;
+            x ^= x >>> 16;
+            return x;
+        }
+
+        public PooledObjectLinkedOpenHashSet<E> getAddCache(final E element) {
+            final E currentAdd = this.lastAddObject.get();
+
+            if (currentAdd == null || !(currentAdd == element || currentAdd.equals(element))) {
+                return null;
+            }
+
+            final PooledObjectLinkedOpenHashSet<E> map = this.lastAddMap.get();
+            if (map == null || map.referenceCount == 0) {
+                // we need to ret null if ref count is zero as calling code will assume the map is in use
+                return null;
+            }
+
+            return map;
+        }
+
+        public PooledObjectLinkedOpenHashSet<E> getRemoveCache(final E element) {
+            final E currentRemove = this.lastRemoveObject.get();
+
+            if (currentRemove == null || !(currentRemove == element || currentRemove.equals(element))) {
+                return null;
+            }
+
+            final PooledObjectLinkedOpenHashSet<E> map = this.lastRemoveMap.get();
+            if (map == null || map.referenceCount == 0) {
+                // we need to ret null if ref count is zero as calling code will assume the map is in use
+                return null;
+            }
+
+            return map;
+        }
+
+        public void updateAddCache(final E element, final PooledObjectLinkedOpenHashSet<E> map) {
+            this.lastAddObject = new WeakReference<>(element);
+            this.lastAddMap = new WeakReference<>(map);
+        }
+
+        public void updateRemoveCache(final E element, final PooledObjectLinkedOpenHashSet<E> map) {
+            this.lastRemoveObject = new WeakReference<>(element);
+            this.lastRemoveMap = new WeakReference<>(map);
+        }
+
+        boolean add(final E element) {
+            boolean added =  this.set.add(element);
+
+            if (added) {
+                this.hash += hash0(element.hashCode());
+            }
+
+            return added;
+        }
+
+        boolean remove(Object element) {
+            boolean removed = this.set.remove(element);
+
+            if (removed) {
+                this.hash -= hash0(element.hashCode());
+            }
+
+            return removed;
+        }
+
+        @Override
+        public Iterator<E> iterator() {
+            return this.set.iterator();
+        }
+
+        @Override
+        public int hashCode() {
+            return this.hash;
+        }
+
+        @Override
+        public boolean equals(final Object other) {
+            if (!(other instanceof PooledObjectLinkedOpenHashSet)) {
+                return false;
+            }
+            if (this.referenceCount == 0) {
+                return other == this;
+            } else {
+                if (other == this) {
+                    // Unfortunately we are never equal to our own instance while in use!
+                    return false;
+                }
+                return this.hash == ((PooledObjectLinkedOpenHashSet)other).hash && this.set.equals(((PooledObjectLinkedOpenHashSet)other).set);
+            }
+        }
+
+        @Override
+        public String toString() {
+            return "PooledHashSet: size: " + this.set.size() + ", reference count: " + this.referenceCount + ", hash: " +
+                this.hashCode() + ", identity: " + System.identityHashCode(this) + " map: " + this.set.toString();
+        }
+    }
+}
diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index ea1117dc86..fe894a68bc 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -741,7 +741,22 @@ public class ChunkProviderServer extends IChunkProvider {
             this.world.timings.countNaturalMobs.startTiming(); // Paper - timings
             int l = this.chunkMapDistance.b();
             EnumCreatureType[] aenumcreaturetype = EnumCreatureType.values();
-            Object2IntMap<EnumCreatureType> object2intmap = this.world.l();
+            // Paper start - per player mob spawning
+            int[] worldMobCount;
+            if (this.playerChunkMap.playerMobDistanceMap != null) {
+                // update distance map
+                this.world.timings.playerMobDistanceMapUpdate.startTiming();
+                this.playerChunkMap.playerMobDistanceMap.update(this.world.players, this.playerChunkMap.viewDistance);
+                this.world.timings.playerMobDistanceMapUpdate.stopTiming();
+                // re-set mob counts
+                for (EntityPlayer player : this.world.players) {
+                    Arrays.fill(player.mobCounts, 0);
+                }
+                worldMobCount = this.world.countMobs(true);
+            } else {
+                worldMobCount = this.world.countMobs(false);
+            }
+            // Paper end
 
             this.world.timings.countNaturalMobs.stopTiming(); // Paper - timings
             this.world.getMethodProfiler().exit();
@@ -809,8 +824,23 @@ public class ChunkProviderServer extends IChunkProvider {
                                 if (enumcreaturetype != EnumCreatureType.MISC && (!enumcreaturetype.c() || this.allowAnimals) && (enumcreaturetype.c() || this.allowMonsters) && (!enumcreaturetype.d() || flag2)) {
                                     int k1 = limit * l / ChunkProviderServer.b; // CraftBukkit - use per-world limits
 
-                                    if (object2intmap.getInt(enumcreaturetype) <= k1) {
-                                        SpawnerCreature.a(enumcreaturetype, this.world, chunk, blockposition);
+                                    // Paper start - only allow spawns upto the limit per chunk and update count afterwards
+                                    int currEntityCount = worldMobCount[enumcreaturetype.ordinal()];
+                                    int difference = k1 - currEntityCount;
+
+                                    if (this.world.paperConfig.perPlayerMobSpawns) {
+                                        int minDiff = Integer.MAX_VALUE;
+                                        for (EntityPlayer entityplayer : this.playerChunkMap.playerMobDistanceMap.getPlayersInRange(chunk.getPos())) {
+                                            minDiff = Math.min(limit - this.playerChunkMap.getMobCountNear(entityplayer, enumcreaturetype), minDiff);
+                                        }
+                                        difference = (minDiff == Integer.MAX_VALUE) ? 0 : minDiff;
+                                    }
+
+                                    if (difference > 0) {
+                                        int spawnCount = SpawnerCreature.spawnMobs(enumcreaturetype, this.world, chunk, blockposition, difference,
+                                            this.world.paperConfig.perPlayerMobSpawns ? this.playerChunkMap::updatePlayerMobTypeMap : null);
+                                        worldMobCount[enumcreaturetype.ordinal()] += spawnCount;
+                                        // Paper end
                                     }
                                 }
                             }
diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
index f375c9507c..fcd887ce30 100644
--- a/src/main/java/net/minecraft/server/EntityPlayer.java
+++ b/src/main/java/net/minecraft/server/EntityPlayer.java
@@ -81,6 +81,11 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
     public boolean queueHealthUpdatePacket = false;
     public net.minecraft.server.PacketPlayOutUpdateHealth queuedHealthUpdatePacket;
     // Paper end
+    // Paper start - mob spawning rework
+    public static final int ENUMCREATURETYPE_TOTAL_ENUMS = EnumCreatureType.values().length;
+    public final int[] mobCounts = new int[ENUMCREATURETYPE_TOTAL_ENUMS]; // Paper
+    public final com.destroystokyo.paper.util.PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> cachedSingleMobDistanceMap;
+    // Paper end
 
     // CraftBukkit start
     public String displayName;
@@ -116,6 +121,7 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
         this.displayName = this.getName();
         this.canPickUpLoot = true;
         this.maxHealthCache = this.getMaxHealth();
+        this.cachedSingleMobDistanceMap = new com.destroystokyo.paper.util.PooledHashSets.PooledObjectLinkedOpenHashSet<>(this); // Paper
     }
 
     // Yes, this doesn't match Vanilla, but it's the best we can do for now.
@@ -1766,6 +1772,7 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
 
     }
 
+    public SectionPosition getPlayerMapSection() { return this.K(); } // Paper - OBFHELPER
     public SectionPosition K() {
         return this.cs;
     }
diff --git a/src/main/java/net/minecraft/server/EntityTypes.java b/src/main/java/net/minecraft/server/EntityTypes.java
index 8427ee2ee8..0f04bcc8b7 100644
--- a/src/main/java/net/minecraft/server/EntityTypes.java
+++ b/src/main/java/net/minecraft/server/EntityTypes.java
@@ -254,6 +254,7 @@ public class EntityTypes<T extends Entity> {
         return this.bf;
     }
 
+    public EnumCreatureType getEnumCreatureType() { return this.e(); } // Paper - OBFHELPER
     public EnumCreatureType e() {
         return this.bb;
     }
diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
index 19603343b2..a7b981f299 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -78,7 +78,8 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
     private final PlayerMap playerMap;
     public final Int2ObjectMap<PlayerChunkMap.EntityTracker> trackedEntities;
     private final Queue<Runnable> z;
-    private int viewDistance;
+    int viewDistance; // Paper - private -> package private
+    public final com.destroystokyo.paper.util.PlayerMobDistanceMap playerMobDistanceMap; // Paper
 
     // CraftBukkit start - recursion-safe executor for Chunk loadCallback() and unloadCallback()
     public final CallbackExecutor callbackExecutor = new CallbackExecutor();
@@ -165,6 +166,24 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
         this.l = supplier;
         this.m = new VillagePlace(new File(this.w, "poi"), datafixer, this.world); // Paper
         this.setViewDistance(i);
+        this.playerMobDistanceMap = this.world.paperConfig.perPlayerMobSpawns ? new com.destroystokyo.paper.util.PlayerMobDistanceMap() : null; // Paper
+    }
+
+    public void updatePlayerMobTypeMap(Entity entity) {
+        if (!this.world.paperConfig.perPlayerMobSpawns) {
+            return;
+        }
+        int chunkX = (int)Math.floor(entity.locX()) >> 4;
+        int chunkZ = (int)Math.floor(entity.locZ()) >> 4;
+        int index = entity.getEntityType().getEnumCreatureType().ordinal();
+
+        for (EntityPlayer player : this.playerMobDistanceMap.getPlayersInRange(chunkX, chunkZ)) {
+            ++player.mobCounts[index];
+        }
+    }
+
+    public int getMobCountNear(EntityPlayer entityPlayer, EnumCreatureType enumCreatureType) {
+        return entityPlayer.mobCounts[enumCreatureType.ordinal()];
     }
 
     private static double a(ChunkCoordIntPair chunkcoordintpair, Entity entity) {
diff --git a/src/main/java/net/minecraft/server/SpawnerCreature.java b/src/main/java/net/minecraft/server/SpawnerCreature.java
index fdac5bb3a2..58bbf2f9d2 100644
--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
+++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
@@ -3,6 +3,7 @@ package net.minecraft.server;
 import java.util.List;
 import java.util.Objects;
 import java.util.Random;
+import java.util.function.Consumer; // Paper
 import javax.annotation.Nullable;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -16,9 +17,14 @@ public final class SpawnerCreature {
 
     private static final Logger LOGGER = LogManager.getLogger();
 
+    // Paper start - add maxSpawns parameter and return spawned mobs
     public static void a(EnumCreatureType enumcreaturetype, WorldServer worldserver, Chunk chunk, BlockPosition blockposition) {
+        spawnMobs(enumcreaturetype, worldserver, chunk, blockposition, Integer.MAX_VALUE, null);
+    }
+    public static int spawnMobs(EnumCreatureType enumcreaturetype, WorldServer worldserver, Chunk chunk, BlockPosition blockposition, int maxSpawns, Consumer<Entity> trackEntity) {
+        // Paper end
         ChunkGenerator<?> chunkgenerator = worldserver.getChunkProvider().getChunkGenerator();
-        int i = 0;
+        int i = 0; // Paper - force diff on name change
         BlockPosition blockposition1 = getRandomPosition(worldserver, chunk);
         int j = blockposition1.getX();
         int k = blockposition1.getY();
@@ -88,7 +94,7 @@ public final class SpawnerCreature {
                                                         );
                                                         if (!event.callEvent()) {
                                                             if (event.shouldAbortSpawn()) {
-                                                                return;
+                                                                return i; // Paper
                                                             }
                                                             ++i2;
                                                             continue;
@@ -107,7 +113,7 @@ public final class SpawnerCreature {
                                                         } catch (Exception exception) {
                                                             SpawnerCreature.LOGGER.warn("Failed to create mob", exception);
                                                             ServerInternalException.reportInternalException(exception); // Paper
-                                                            return;
+                                                            return i; // Paper
                                                         }
 
                                                         entityinsentient.setPositionRotation((double) f, (double) k, (double) f1, worldserver.random.nextFloat() * 360.0F, 0.0F);
@@ -115,12 +121,16 @@ public final class SpawnerCreature {
                                                             groupdataentity = entityinsentient.prepare(worldserver, worldserver.getDamageScaler(new BlockPosition(entityinsentient)), EnumMobSpawn.NATURAL, groupdataentity, (NBTTagCompound) null);
                                                             // CraftBukkit start
                                                             if (worldserver.addEntity(entityinsentient, SpawnReason.NATURAL)) {
-                                                                ++i;
+                                                                ++i; // Paper - force diff on name change
                                                                 ++i2;
+                                                                if (trackEntity != null) {
+                                                                    trackEntity.accept(entityinsentient); // Paper
+                                                                }
                                                             }
+                                                            if (i >= maxSpawns) { return i; } // Paper
                                                             // CraftBukkit end
                                                             if (i >= entityinsentient.getMaxSpawnGroup()) {
-                                                                return;
+                                                                return i; // Paper
                                                             }
 
                                                             if (entityinsentient.c(i2)) {
@@ -146,6 +156,7 @@ public final class SpawnerCreature {
 
             }
         }
+        return i; // Paper
     }
 
     @Nullable
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index f9aed78188..fd8ca2a510 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -1028,7 +1028,20 @@ public class WorldServer extends World {
     }
 
     public Object2IntMap<EnumCreatureType> l() {
-        Object2IntMap<EnumCreatureType> object2intmap = new Object2IntOpenHashMap();
+        // Paper start
+        int[] values = this.countMobs(false);
+        EnumCreatureType[] byId = EnumCreatureType.values();
+        Object2IntMap<EnumCreatureType> ret = new Object2IntOpenHashMap<>();
+
+        for (int i = 0, len = values.length; i < len; ++i) {
+            ret.put(byId[i], values[i]);
+        }
+
+        return ret;
+    }
+    public int[] countMobs(boolean updatePlayerCounts) {
+        int[] ret = new int[EntityPlayer.ENUMCREATURETYPE_TOTAL_ENUMS];
+        // Paper end
         ObjectIterator objectiterator = this.entitiesById.values().iterator();
 
         while (objectiterator.hasNext()) {
@@ -1053,11 +1066,16 @@ public class WorldServer extends World {
                     continue;
                 }
                 // Paper end
-                object2intmap.mergeInt(enumcreaturetype, 1, Integer::sum);
+                // Paper start - rework mob spawning
+                if (updatePlayerCounts) {
+                    this.getChunkProvider().playerChunkMap.updatePlayerMobTypeMap(entity);
+                }
+                ++ret[enumcreaturetype.ordinal()];
+                // Paper end
             }
         }
 
-        return object2intmap;
+        return ret;
     }
 
     @Override
-- 
2.26.2