From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Bjarne Koll <lynxplay101@gmail.com>
Date: Wed, 3 Mar 2021 12:48:48 +0100
Subject: [PATCH] Remove streams from SensorNearest

The behavioural nearby sensors are validated every tick on the entities
that registered the respective sensors and are therefore a good subject
to performance improvements.

More specifically this commit replaces the Stream#filter usage with
ArrayList#removeIf as the removeIf method on an array list is heavily
optimized towards a single internal array re-allocation without any
further overhead on the removeIf call.

The only negative of this change is the rather agressive diff these
patches introduce as the methods are basically being reimplemented
compared to the previous stream-based implementation.

See: https://nipafx.dev/java-stream-performance/

diff --git a/src/main/java/net/minecraft/world/entity/ai/sensing/NearestItemSensor.java b/src/main/java/net/minecraft/world/entity/ai/sensing/NearestItemSensor.java
index 7680c269c2fe0cf2a51d0ebeb34624181826d578..49f3b25d28072b61f5cc97260df61df892a58714 100644
--- a/src/main/java/net/minecraft/world/entity/ai/sensing/NearestItemSensor.java
+++ b/src/main/java/net/minecraft/world/entity/ai/sensing/NearestItemSensor.java
@@ -28,11 +28,15 @@ public class NearestItemSensor extends Sensor<Mob> {
             return true;
         });
         list.sort(Comparator.comparingDouble(entity::distanceToSqr));
-        Optional<ItemEntity> optional = list.stream().filter((itemEntity) -> {
-            return entity.wantsToPickUp(itemEntity.getItem());
-        }).filter((itemEntity) -> {
-            return itemEntity.closerThan(entity, 9.0D);
-        }).filter(entity::hasLineOfSight).findFirst();
-        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_WANTED_ITEM, optional);
+        // Paper start - remove streams in favour of lists
+        ItemEntity nearest = null;
+        for (ItemEntity entityItem : list) {
+            if (entity.wantsToPickUp(entityItem.getItem()) && entityItem.closerThan(entity, 9.0D) && entity.hasLineOfSight(entityItem)) {
+                nearest = entityItem;
+                break;
+            }
+        }
+        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_WANTED_ITEM, Optional.ofNullable(nearest));
+        // Paper end
     }
 }
diff --git a/src/main/java/net/minecraft/world/entity/ai/sensing/NearestLivingEntitySensor.java b/src/main/java/net/minecraft/world/entity/ai/sensing/NearestLivingEntitySensor.java
index 66c90013e52170a657b1a5dbdb99748a19fe55e8..ffd83db0a419ab589e89feeddd3fb038d6ed5839 100644
--- a/src/main/java/net/minecraft/world/entity/ai/sensing/NearestLivingEntitySensor.java
+++ b/src/main/java/net/minecraft/world/entity/ai/sensing/NearestLivingEntitySensor.java
@@ -21,9 +21,11 @@ public class NearestLivingEntitySensor extends Sensor<LivingEntity> {
         list.sort(Comparator.comparingDouble(entity::distanceToSqr));
         Brain<?> brain = entity.getBrain();
         brain.setMemory(MemoryModuleType.NEAREST_LIVING_ENTITIES, list);
-        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_LIVING_ENTITIES, list.stream().filter((livingEntity2) -> {
-            return isEntityTargetable(entity, livingEntity2);
-        }).collect(Collectors.toList()));
+        // Paper start - remove streams in favour of lists
+        List<LivingEntity> visibleMobs = new java.util.ArrayList<>(list);
+        visibleMobs.removeIf(otherEntityLiving -> !Sensor.isEntityTargetable(entity, otherEntityLiving));
+        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_LIVING_ENTITIES, visibleMobs);
+        // Paper end
     }
 
     @Override
diff --git a/src/main/java/net/minecraft/world/entity/ai/sensing/PlayerSensor.java b/src/main/java/net/minecraft/world/entity/ai/sensing/PlayerSensor.java
index b51574548b370f8a86d27835e9888ce1cd1d18be..457ea75137b8b02dc32bf1769ae8d57c470da470 100644
--- a/src/main/java/net/minecraft/world/entity/ai/sensing/PlayerSensor.java
+++ b/src/main/java/net/minecraft/world/entity/ai/sensing/PlayerSensor.java
@@ -21,18 +21,25 @@ public class PlayerSensor extends Sensor<LivingEntity> {
 
     @Override
     protected void doTick(ServerLevel world, LivingEntity entity) {
-        List<Player> list = world.players().stream().filter(EntitySelector.NO_SPECTATORS).filter((serverPlayer) -> {
-            return entity.closerThan(serverPlayer, 16.0D);
-        }).sorted(Comparator.comparingDouble(entity::distanceToSqr)).collect(Collectors.toList());
+        // Paper start - remove streams in favour of lists
+        List<Player> players = new java.util.ArrayList<>(world.players());
+        players.removeIf(player -> !EntitySelector.NO_SPECTATORS.test(player) || !entity.closerThan(player, 16.0D)); // Paper - removeIf only re-allocates once compared to iterator
         Brain<?> brain = entity.getBrain();
-        brain.setMemory(MemoryModuleType.NEAREST_PLAYERS, list);
-        List<Player> list2 = list.stream().filter((player) -> {
-            return isEntityTargetable(entity, player);
-        }).collect(Collectors.toList());
-        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_PLAYER, list2.isEmpty() ? null : list2.get(0));
-        Optional<Player> optional = list2.stream().filter((player) -> {
-            return isEntityAttackable(entity, player);
-        }).findFirst();
-        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_ATTACKABLE_PLAYER, optional);
+
+        brain.setMemory(MemoryModuleType.NEAREST_PLAYERS, players);
+
+        Player nearest = null, nearestTargetable = null;
+        for (Player player : players) {
+            if (Sensor.isEntityTargetable(entity, player)) {
+                if (nearest == null) nearest = player;
+                if (Sensor.isEntityAttackable(entity, player)) {
+                    nearestTargetable = player;
+                    break; // Both variables are assigned, no reason to loop further
+                }
+            }
+        }
+        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_PLAYER, nearest);
+        brain.setMemory(MemoryModuleType.NEAREST_VISIBLE_ATTACKABLE_PLAYER, nearestTargetable);
+        // Paper end
     }
 }