PaperMC/Spigot-Server-Patches/0448-Reduce-entity-tracker-updates-on-move.patch

From 0fc9d917fe39a561141036c82cca603f2640c7d0 Mon Sep 17 00:00:00 2001
From: froobynooby <froobynooby@froobworld.com>
Date: Thu, 20 Feb 2020 15:50:49 +0930
Subject: [PATCH] Reduce entity tracker updates on move

With this patch, for each player we keep track of a set of
entities that the player is tracking. This is used to split
the entity tracker update logic in the movePlayer method in
PlayerChunkMap in to two parts:
* Full update: Run through all entity trackers and update them
* Partial update: Run through all entity trackers for entities
the player is already tracking and update them

Partial updates will always take less time than full updates,
usually by a considerable amount if players and entities are
spread out over the map. Assuming they are evenly spread,
and given there are x many players, it would be expected to
take 1/x the time of a full update.

Full updates are only run if the following conditions are met:
* It has been 20 ticks since the last full update
* The player has moved over set distance since the last full
update (distance is configurable)

The motivation for the first condition is that the client
sends the server its position once a second, which calls
movePlayer, so at a minimum we want to be sending the player
an updated set of entities it can see every second.

The motivation for the second condition is that looping
through every entity in world to check if it is now within
the tracking range after the player has moved 0.1 blocks is
largely unnecessary. Checking only after the player has moved
1 or 2 blocks is far better for performance, and very unlikely
to give any noticeable side effects.

In testing, this has reduced the time taken for movement
packet processing by up to 4x. Packet processing for movement
packets often show up as a major contributor to TPS loss in
servers with large player counts

diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index 7ca67a4aa5..e93176d8f2 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -668,4 +668,9 @@ public class PaperWorldConfig {
     private void zombieVillagerInfectionChance() {
         zombieVillagerInfectionChance = getDouble("zombie-villager-infection-chance", zombieVillagerInfectionChance);
     }
+
+    public double trackerUpdateDistance = 1;
+    private void trackerUpdateDistance() {
+        trackerUpdateDistance = getDouble("tracker-update-distance", trackerUpdateDistance);
+    }
 }
diff --git a/src/main/java/net/minecraft/server/EntityPlayer.java b/src/main/java/net/minecraft/server/EntityPlayer.java
index e7bfbc3307..43774bc9a5 100644
--- a/src/main/java/net/minecraft/server/EntityPlayer.java
+++ b/src/main/java/net/minecraft/server/EntityPlayer.java
@@ -86,6 +86,10 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
     public final int[] mobCounts = new int[ENUMCREATURETYPE_TOTAL_ENUMS]; // Paper
     public final com.destroystokyo.paper.util.PooledHashSets.PooledObjectLinkedOpenHashSet<EntityPlayer> cachedSingleMobDistanceMap;
     // Paper end
+    // Paper start - Reduce entity tracker updates on move
+    public Vec3D lastTrackedPosition = new Vec3D(0, 0, 0);
+    public long lastTrackedTick;
+    // Paper end
 
     // CraftBukkit start
     public String displayName;
diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
index f564502f81..0186ab9e40 100644
--- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
+++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
@@ -133,6 +133,39 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
     }
 
 
+    // Paper end
+
+    // Paper start - Reduce entity tracker updates on move
+    private double trackerUpdateDistanceSquared;
+    private final Int2ObjectMap<Int2ObjectMap<PlayerChunkMap.EntityTracker>> playerTrackedEntities = new Int2ObjectOpenHashMap<>();
+    private final Int2ObjectMap<Queue<Integer>> playerTrackedEntitiesRemoveQueue = new Int2ObjectOpenHashMap<>();
+
+    void flushRemoveQueue(EntityPlayer entityplayer) {
+        Queue<Integer> removeQueue = getPlayerTrackedEntityMapRemoveQueue(entityplayer.getId());
+        Int2ObjectMap<PlayerChunkMap.EntityTracker> entityMap = getPlayerTrackedEntityMap(entityplayer.getId());
+        for (Integer id = removeQueue.poll(); id != null; id = removeQueue.poll()) {
+            entityMap.remove(id);
+        }
+    }
+
+    void flushRemoveQueues() {
+        for (Int2ObjectMap.Entry<Queue<Integer>> entry : playerTrackedEntitiesRemoveQueue.int2ObjectEntrySet()) {
+            Int2ObjectMap<EntityTracker> entityMap = getPlayerTrackedEntityMap(entry.getKey());
+            Queue<Integer> removeQueue = entry.getValue();
+            for (Integer id = removeQueue.poll(); id != null; id = removeQueue.poll()) {
+                entityMap.remove(id);
+            }
+        }
+    }
+
+    Int2ObjectMap<EntityTracker> getPlayerTrackedEntityMap(int id) {
+        return playerTrackedEntities.computeIfAbsent(id, i -> new Int2ObjectOpenHashMap<>());
+    }
+
+    Queue<Integer> getPlayerTrackedEntityMapRemoveQueue(int id) {
+        return playerTrackedEntitiesRemoveQueue.computeIfAbsent(id, i -> new java.util.ArrayDeque<>());
+    }
+
     // Paper end
 
     public PlayerChunkMap(WorldServer worldserver, File file, DataFixer datafixer, DefinedStructureManager definedstructuremanager, Executor executor, IAsyncTaskHandler<Runnable> iasynctaskhandler, ILightAccess ilightaccess, ChunkGenerator<?> chunkgenerator, WorldLoadListener worldloadlistener, Supplier<WorldPersistentData> supplier, int i) {
@@ -167,6 +200,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
         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
+        this.trackerUpdateDistanceSquared = Math.pow(this.world.paperConfig.trackerUpdateDistance, 2); // Paper
     }
 
     public void updatePlayerMobTypeMap(Entity entity) {
@@ -1334,8 +1368,19 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
     }
 
     public void movePlayer(EntityPlayer entityplayer) {
-        ObjectIterator objectiterator = this.trackedEntities.values().iterator();
+        // Paper start
+        // ObjectIterator objectiterator = this.trackedEntities.values().iterator();
+        ObjectIterator objectiterator;
 
+        if (MinecraftServer.currentTick - entityplayer.lastTrackedTick >= 20
+            || entityplayer.lastTrackedPosition.distanceSquared(entityplayer.getPositionVector()) >= trackerUpdateDistanceSquared) {
+            entityplayer.lastTrackedPosition = entityplayer.getPositionVector();
+            entityplayer.lastTrackedTick = MinecraftServer.currentTick;
+            objectiterator = this.trackedEntities.values().iterator(); // Update all entity trackers
+        } else {
+            objectiterator = getPlayerTrackedEntityMap(entityplayer.getId()).values().iterator(); // Only update entity trackers for already tracked entities
+        }
+        // Paper end
         while (objectiterator.hasNext()) {
             PlayerChunkMap.EntityTracker playerchunkmap_entitytracker = (PlayerChunkMap.EntityTracker) objectiterator.next();
 
@@ -1345,6 +1390,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
                 playerchunkmap_entitytracker.updatePlayer(entityplayer);
             }
         }
+        flushRemoveQueues(); // Paper
 
         int i = MathHelper.floor(entityplayer.locX()) >> 4;
         int j = MathHelper.floor(entityplayer.locZ()) >> 4;
@@ -1486,12 +1532,21 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
 
                 playerchunkmap_entitytracker.clear(entityplayer);
             }
+            // Paper start
+            playerTrackedEntities.remove(entityplayer.getId());
+            playerTrackedEntitiesRemoveQueue.remove(entityplayer.getId());
+            // Paper end
         }
 
         PlayerChunkMap.EntityTracker playerchunkmap_entitytracker1 = (PlayerChunkMap.EntityTracker) this.trackedEntities.remove(entity.getId());
 
         if (playerchunkmap_entitytracker1 != null) {
             playerchunkmap_entitytracker1.a();
+            // Paper start
+            for (EntityPlayer player : playerchunkmap_entitytracker1.trackedPlayers) {
+                getPlayerTrackedEntityMap(player.getId()).remove(playerchunkmap_entitytracker1.tracker.getId());
+            }
+            // Paper end
         }
         entity.tracker = null; // Paper - We're no longer tracked
     }
@@ -1532,7 +1587,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
             }
             world.timings.tracker2.stopTiming(); // Paper
         }
-
+        flushRemoveQueues(); // Paper
 
     }
 
@@ -1581,6 +1636,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
                 }
             }
         }
+        flushRemoveQueue(entityplayer); // Paper
 
         Iterator iterator;
         Entity entity1;
@@ -1677,6 +1733,7 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
             org.spigotmc.AsyncCatcher.catchOp("player tracker clear"); // Spigot
             if (this.trackedPlayers.remove(entityplayer)) {
                 this.trackerEntry.a(entityplayer);
+                getPlayerTrackedEntityMap(entityplayer.getId()).remove(this.tracker.getId()); // Paper
             }
 
         }
@@ -1713,9 +1770,11 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
 
                     if (flag1 && this.trackedPlayerMap.putIfAbsent(entityplayer, true) == null) { // Paper
                         this.trackerEntry.b(entityplayer);
+                        getPlayerTrackedEntityMap(entityplayer.getId()).put(this.tracker.getId(), this); // Paper
                     }
                 } else if (this.trackedPlayers.remove(entityplayer)) {
                     this.trackerEntry.a(entityplayer);
+                    getPlayerTrackedEntityMapRemoveQueue(entityplayer.getId()).add(this.tracker.getId()); // Paper
                 }
 
             }
-- 
2.25.1