Paper/Spigot-Server-Patches/0375-implement-optional-per-player-mob-spawns.patch

From 0000000000000000000000000000000000000000 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 a27dc38d1a29ed1d63d2f44b7984c2b65be487d9..96aaaab5b7685c874463505f9d25e8a0a01a6e7c 100644
--- a/src/main/java/co/aikar/timings/WorldTimingsHandler.java
+++ b/src/main/java/co/aikar/timings/WorldTimingsHandler.java
@@ -57,6 +57,7 @@ public class WorldTimingsHandler {
 
 
     public final Timing miscMobSpawning;
+    public final Timing playerMobDistanceMapUpdate;
 
     public final Timing poiUnload;
     public final Timing chunkUnload;
@@ -122,6 +123,7 @@ 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 53ededbb615ec608e91ee87f46301a3c2964a7a3..5479c544ed43bf4e3d04626d5a1ff3c3084f9d4e 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -553,4 +553,9 @@ 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 0000000000000000000000000000000000000000..9ebd7ecb7a0ac73ccacf34c097056598bb5d26e8
--- /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 0000000000000000000000000000000000000000..4f13d3ff8391793a99f067189f854078334499c6
--- /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 7278e39d7fb47737b783c482f4c74a82ded163f8..5b60777c63d54b74b3de5a7373f64ba99fb85d61 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -745,7 +745,22 @@ public class ChunkProviderServer extends IChunkProvider {
             this.world.getMethodProfiler().enter("naturalSpawnCount");
             this.world.timings.countNaturalMobs.startTiming(); // Paper - timings
             int l = this.chunkMapDistance.b();
-            SpawnerCreature.d spawnercreature_d = SpawnerCreature.a(l, this.world.A(), this::a);
+            // Paper start - per player mob spawning
+            SpawnerCreature.d spawnercreature_d; // moved down
+            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);
+                }
+                spawnercreature_d = SpawnerCreature.countMobs(l, this.world.A(), this::a, true);
+            } else {
+                spawnercreature_d = SpawnerCreature.countMobs(l, this.world.A(), this::a, false);
+            }
+            // Paper end
             this.world.timings.countNaturalMobs.stopTiming(); // Paper - timings
 
             this.p = spawnercreature_d;
diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
index 1a8d8bc120fec876c528029dcc2804519caa569f..bb79467c6bb0ed44057802dde6cd40fa81c8d4fd 100644
--- a/src/main/java/net/minecraft/server/EntityPlayer.java
+++ b/src/main/java/net/minecraft/server/EntityPlayer.java
@@ -89,6 +89,11 @@ 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;
@@ -125,6 +130,7 @@ 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.
@@ -1904,6 +1910,7 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
 
     }
 
+    public final SectionPosition getPlayerMapSection() { return this.O(); } // Paper - OBFHELPER
     public SectionPosition O() {
         return this.cj;
     }
diff --git a/src/main/java/net/minecraft/server/EntityTypes.java b/src/main/java/net/minecraft/server/EntityTypes.java
index ebffa433a4df6e573db76d95762a169d02658d72..8540d88f98f5626a79fedd1329782000a2ee7012 100644
--- a/src/main/java/net/minecraft/server/EntityTypes.java
+++ b/src/main/java/net/minecraft/server/EntityTypes.java
@@ -280,6 +280,7 @@ public class EntityTypes<T extends Entity> {
         return this.bl;
     }
 
+    public final EnumCreatureType getEnumCreatureType() { return this.e(); } // Paper - OBFHELPER
     public EnumCreatureType e() {
         return this.bg;
     }
diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
index e7d9674e25c06090d57bba6c8229bc3b75cb67e6..70a291090f022ff7d79a75b94ac54b94ff6db751 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -81,7 +81,8 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
     public final Int2ObjectMap<PlayerChunkMap.EntityTracker> trackedEntities;
     private final Long2ByteMap z;
     private final Queue<Runnable> A; private final Queue<Runnable> getUnloadQueueTasks() { return this.A; } // Paper - OBFHELPER
-    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();
@@ -160,6 +161,24 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
         this.l = supplier;
         this.m = new VillagePlace(new File(this.w, "poi"), datafixer, flag, 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 99d4d6b4bdedcba7964ddc99467b8f8e5229b98a..beaea041dc47635411542fe9d06690809e03bf9e 100644
--- a/src/main/java/net/minecraft/server/SpawnerCreature.java
+++ b/src/main/java/net/minecraft/server/SpawnerCreature.java
@@ -29,6 +29,11 @@ public final class SpawnerCreature {
     });
 
     public static SpawnerCreature.d a(int i, Iterable<Entity> iterable, SpawnerCreature.b spawnercreature_b) {
+        // Paper start - add countMobs parameter
+        return countMobs(i, iterable, spawnercreature_b, false);
+    }
+    public static SpawnerCreature.d countMobs(int i, Iterable<Entity> iterable, SpawnerCreature.b spawnercreature_b, boolean countMobs) {
+        // Paper end - add countMobs parameter
         SpawnerCreatureProbabilities spawnercreatureprobabilities = new SpawnerCreatureProbabilities();
         Object2IntOpenHashMap<EnumCreatureType> object2intopenhashmap = new Object2IntOpenHashMap();
         Iterator iterator = iterable.iterator();
@@ -66,6 +71,11 @@ public final class SpawnerCreature {
                     }
 
                     object2intopenhashmap.addTo(enumcreaturetype, 1);
+                    // Paper start
+                    if (countMobs) {
+                        ((WorldServer)chunk.world).getChunkProvider().playerChunkMap.updatePlayerMobTypeMap(entity);
+                    }
+                    // Paper end
                 });
             }
         }
@@ -124,13 +134,33 @@ public final class SpawnerCreature {
                 continue;
             }
 
-            if ((flag || !enumcreaturetype.d()) && (flag1 || enumcreaturetype.d()) && (flag2 || !enumcreaturetype.e()) && spawnercreature_d.a(enumcreaturetype, limit)) {
+            // Paper start - only allow spawns upto the limit per chunk and update count afterwards
+            int currEntityCount = spawnercreature_d.getEntityCountsByType().getInt(enumcreaturetype);
+            int k1 = limit * spawnercreature_d.getSpawnerChunks() / SpawnerCreature.b;
+            int difference = k1 - currEntityCount;
+
+            if (worldserver.paperConfig.perPlayerMobSpawns) {
+                int minDiff = Integer.MAX_VALUE;
+                for (EntityPlayer entityplayer : worldserver.getChunkProvider().playerChunkMap.playerMobDistanceMap.getPlayersInRange(chunk.getPos())) {
+                    minDiff = Math.min(limit - worldserver.getChunkProvider().playerChunkMap.getMobCountNear(entityplayer, enumcreaturetype), minDiff);
+                }
+                difference = (minDiff == Integer.MAX_VALUE) ? 0 : minDiff;
+            }
+            // Paper end
+
+            // Paper start - per player mob spawning
+            if ((flag || !enumcreaturetype.d()) && (flag1 || enumcreaturetype.d()) && (flag2 || !enumcreaturetype.e()) && difference > 0) {
                 // CraftBukkit end
-                a(enumcreaturetype, worldserver, chunk, (entitytypes, blockposition, ichunkaccess) -> {
+                int spawnCount = spawnMobs(enumcreaturetype, worldserver, chunk, (entitytypes, blockposition, ichunkaccess) -> {
                     return spawnercreature_d.a(entitytypes, blockposition, ichunkaccess);
                 }, (entityinsentient, ichunkaccess) -> {
                     spawnercreature_d.a(entityinsentient, ichunkaccess);
+                },
+                difference, worldserver.paperConfig.perPlayerMobSpawns ? worldserver.getChunkProvider().playerChunkMap::updatePlayerMobTypeMap : null);
+                spawnercreature_d.getEntityCountsByType().mergeInt(enumcreaturetype, spawnCount, (keyInMap, valueInMap) -> {
+                    return Integer.valueOf(spawnCount + valueInMap.intValue());
                 });
+                // Paper end - per player mob spawning
             }
         }
 
@@ -139,22 +169,34 @@ public final class SpawnerCreature {
     }
 
     public static void a(EnumCreatureType enumcreaturetype, WorldServer worldserver, Chunk chunk, SpawnerCreature.c spawnercreature_c, SpawnerCreature.a spawnercreature_a) {
+        // Paper start - add parameters and int ret type
+        spawnMobs(enumcreaturetype, worldserver, chunk, spawnercreature_c, spawnercreature_a, Integer.MAX_VALUE, null);
+    }
+    public static int spawnMobs(EnumCreatureType enumcreaturetype, WorldServer worldserver, Chunk chunk, SpawnerCreature.c spawnercreature_c, SpawnerCreature.a spawnercreature_a, int maxSpawns, Consumer<Entity> trackEntity) {
+        // Paper end - add parameters and int ret type
         BlockPosition blockposition = getRandomPosition(worldserver, chunk);
 
         if (blockposition.getY() >= 1) {
-            a(enumcreaturetype, worldserver, (IChunkAccess) chunk, blockposition, spawnercreature_c, spawnercreature_a);
+            return spawnMobsInternal(enumcreaturetype, worldserver, (IChunkAccess) chunk, blockposition, spawnercreature_c, spawnercreature_a, maxSpawns, trackEntity);
         }
+        return 0; // Paper
     }
 
     public static void a(EnumCreatureType enumcreaturetype, WorldServer worldserver, IChunkAccess ichunkaccess, BlockPosition blockposition, SpawnerCreature.c spawnercreature_c, SpawnerCreature.a spawnercreature_a) {
+        // Paper start - add maxSpawns parameter and return spawned mobs
+        spawnMobsInternal(enumcreaturetype, worldserver, ichunkaccess, blockposition, spawnercreature_c, spawnercreature_a, Integer.MAX_VALUE, null);
+    }
+    public static int spawnMobsInternal(EnumCreatureType enumcreaturetype, WorldServer worldserver, IChunkAccess ichunkaccess, BlockPosition blockposition, SpawnerCreature.c spawnercreature_c, SpawnerCreature.a spawnercreature_a, int maxSpawns, Consumer<Entity> trackEntity) {
+        // Paper end - add maxSpawns parameter and return spawned mobs
         StructureManager structuremanager = worldserver.getStructureManager();
         ChunkGenerator chunkgenerator = worldserver.getChunkProvider().getChunkGenerator();
         int i = blockposition.getY();
         IBlockData iblockdata = worldserver.getTypeIfLoadedAndInBounds(blockposition); // Paper - don't load chunks for mob spawn
+        int j = 0; // Paper - moved up
 
         if (iblockdata != null && !iblockdata.isOccluding(ichunkaccess, blockposition)) { // Paper - don't load chunks for mob spawn
             BlockPosition.MutableBlockPosition blockposition_mutableblockposition = new BlockPosition.MutableBlockPosition();
-            int j = 0;
+            // Paper - moved up
             int k = 0;
 
             while (k < 3) {
@@ -194,7 +236,7 @@ public final class SpawnerCreature {
                                     // Paper start
                                     Boolean doSpawning = a(worldserver, enumcreaturetype, structuremanager, chunkgenerator, biomesettingsmobs_c, blockposition_mutableblockposition, d2);
                                     if (doSpawning == null) {
-                                        return;
+                                        return j; // Paper
                                     }
                                     if (doSpawning && spawnercreature_c.test(biomesettingsmobs_c.c, blockposition_mutableblockposition, ichunkaccess)) {
                                         // Paper end
@@ -202,7 +244,7 @@ public final class SpawnerCreature {
 
 
                                         if (entityinsentient == null) {
-                                            return;
+                                            return j; // Paper
                                         }
 
                                         entityinsentient.setPositionRotation(d0, (double) i, d1, worldserver.random.nextFloat() * 360.0F, 0.0F);
@@ -210,13 +252,18 @@ public final class SpawnerCreature {
                                             groupdataentity = entityinsentient.prepare(worldserver, worldserver.getDamageScaler(entityinsentient.getChunkCoordinates()), EnumMobSpawn.NATURAL, groupdataentity, (NBTTagCompound) null);
                                             // CraftBukkit start
                                             if (worldserver.addAllEntities(entityinsentient, SpawnReason.NATURAL)) {
-                                                ++j;
+                                                ++j; // Paper - force diff on name change - we expect this to be the total amount spawned
                                                 ++k1;
                                                 spawnercreature_a.run(entityinsentient, ichunkaccess);
+                                                // Paper start
+                                                if (trackEntity != null) {
+                                                    trackEntity.accept(entityinsentient);
+                                                }
+                                                // Paper end
                                             }
                                             // CraftBukkit end
-                                            if (j >= entityinsentient.getMaxSpawnGroup()) {
-                                                return;
+                                            if (j >= entityinsentient.getMaxSpawnGroup() || j >= maxSpawns) { // Paper
+                                                return j; // Paper
                                             }
 
                                             if (entityinsentient.c(k1)) {
@@ -238,6 +285,7 @@ public final class SpawnerCreature {
             }
 
         }
+        return j; // Paper
     }
 
     private static boolean a(WorldServer worldserver, IChunkAccess ichunkaccess, BlockPosition.MutableBlockPosition blockposition_mutableblockposition, double d0) {
@@ -478,8 +526,8 @@ public final class SpawnerCreature {
 
     public static class d {
 
-        private final int a;
-        private final Object2IntOpenHashMap<EnumCreatureType> b;
+        private final int a; final int getSpawnerChunks() { return this.a; } // Paper - OBFHELPER
+        private final Object2IntOpenHashMap<EnumCreatureType> b; final Object2IntMap<EnumCreatureType> getEntityCountsByType() { return this.b; } // Paper - OBFHELPER
         private final SpawnerCreatureProbabilities c;
         private final Object2IntMap<EnumCreatureType> d;
         @Nullable
@@ -540,7 +588,7 @@ public final class SpawnerCreature {
 
         // CraftBukkit start
         private boolean a(EnumCreatureType enumcreaturetype, int limit) {
-            int i = limit * this.a / SpawnerCreature.b;
+            int i = limit * this.a / SpawnerCreature.b; // Paper - diff on change, needed in the spawn method
             // CraftBukkit end
 
             return this.b.getInt(enumcreaturetype) < i;