Paper/patches/server/0987-Optimize-Pathfinder-Remove-Streams-Optimized-collect.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Tue, 4 Aug 2020 22:24:15 +0200
Subject: [PATCH] Optimize Pathfinder - Remove Streams / Optimized collections

I utilized the IDE to convert streams to non streams code, so shouldn't
be any risk of behavior change. Only did minor optimization of the
generated code set to remove unnecessary things.

I expect us to just drop this patch on next major update and re-apply
it with the IDE again and re-apply the collections optimization.

Optimize collection by creating a list instead of a set of the key and value.

This lets us get faster foreach iteration, as well as avoids map lookups on
the values when needed.

Feature patch

diff --git a/src/main/java/net/minecraft/world/level/pathfinder/PathFinder.java b/src/main/java/net/minecraft/world/level/pathfinder/PathFinder.java
index 17006cd22152cf942455437ff7b21a8645259578..cc7d94144e39f7dace7b569b4567def98396e8f9 100644
--- a/src/main/java/net/minecraft/world/level/pathfinder/PathFinder.java
+++ b/src/main/java/net/minecraft/world/level/pathfinder/PathFinder.java
@@ -43,8 +43,12 @@ public class PathFinder {
         if (node == null) {
             return null;
         } else {
-            Map<Target, BlockPos> map = positions.stream()
-                .collect(Collectors.toMap(pos -> this.nodeEvaluator.getTarget((double)pos.getX(), (double)pos.getY(), (double)pos.getZ()), Function.identity()));
+            // Paper start - Perf: remove streams and optimize collection
+            List<Map.Entry<Target, BlockPos>> map = Lists.newArrayList();
+            for (final BlockPos pos : positions) {
+                map.add(new java.util.AbstractMap.SimpleEntry<>(this.nodeEvaluator.getTarget(pos.getX(), pos.getY(), pos.getZ()), pos));
+            }
+            // Paper end - Perf: remove streams and optimize collection
             Path path = this.findPath(node, map, followRange, distance, rangeMultiplier);
             this.nodeEvaluator.done();
             return path;
@@ -52,19 +56,20 @@ public class PathFinder {
     }
 
     @Nullable
-    private Path findPath(Node startNode, Map<Target, BlockPos> positions, float followRange, int distance, float rangeMultiplier) {
+    // Paper start - Perf: remove streams and optimize collection
+    private Path findPath(Node startNode, List<Map.Entry<Target, BlockPos>> positions, float followRange, int distance, float rangeMultiplier) {
         ProfilerFiller profilerFiller = Profiler.get();
         profilerFiller.push("find_path");
         profilerFiller.markForCharting(MetricCategory.PATH_FINDING);
-        Set<Target> set = positions.keySet();
+        // Set<Target> set = positions.keySet();
         startNode.g = 0.0F;
-        startNode.h = this.getBestH(startNode, set);
+        startNode.h = this.getBestH(startNode, positions); // Paper - optimize collection
         startNode.f = startNode.h;
         this.openSet.clear();
         this.openSet.insert(startNode);
-        Set<Node> set2 = ImmutableSet.of();
+        // Set<Node> set2 = ImmutableSet.of(); // Paper - unused - diff on change
         int i = 0;
-        Set<Target> set3 = Sets.newHashSetWithExpectedSize(set.size());
+        List<Map.Entry<Target, BlockPos>> entryList = Lists.newArrayListWithExpectedSize(positions.size()); // Paper - optimize collection
         int j = (int)((float)this.maxVisitedNodes * rangeMultiplier);
 
         while (!this.openSet.isEmpty()) {
@@ -75,14 +80,18 @@ public class PathFinder {
             Node node = this.openSet.pop();
             node.closed = true;
 
-            for (Target target : set) {
+            // Paper start - optimize collection
+            for (int i1 = 0; i1 < positions.size(); i1++) {
+                final Map.Entry<Target, BlockPos> entry = positions.get(i1);
+                Target target = entry.getKey();
                 if (node.distanceManhattan(target) <= (float)distance) {
                     target.setReached();
-                    set3.add(target);
+                    entryList.add(entry);
+                    // Paper end - Perf: remove streams and optimize collection
                 }
             }
 
-            if (!set3.isEmpty()) {
+            if (!entryList.isEmpty()) { // Paper - Perf: remove streams and optimize collection; rename
                 break;
             }
 
@@ -97,7 +106,7 @@ public class PathFinder {
                     if (node2.walkedDistance < followRange && (!node2.inOpenSet() || g < node2.g)) {
                         node2.cameFrom = node;
                         node2.g = g;
-                        node2.h = this.getBestH(node2, set) * 1.5F;
+                        node2.h = this.getBestH(node2, positions) * 1.5F; // Paper - Perf: remove streams and optimize collection
                         if (node2.inOpenSet()) {
                             this.openSet.changeCost(node2, node2.g + node2.h);
                         } else {
@@ -109,23 +118,32 @@ public class PathFinder {
             }
         }
 
-        Optional<Path> optional = !set3.isEmpty()
-            ? set3.stream().map(node -> this.reconstructPath(node.getBestNode(), positions.get(node), true)).min(Comparator.comparingInt(Path::getNodeCount))
-            : set.stream()
-                .map(targetx -> this.reconstructPath(targetx.getBestNode(), positions.get(targetx), false))
-                .min(Comparator.comparingDouble(Path::getDistToTarget).thenComparingInt(Path::getNodeCount));
+        // Paper start - Perf: remove streams and optimize collection
+        Path best = null;
+        boolean entryListIsEmpty = entryList.isEmpty();
+        Comparator<Path> comparator = entryListIsEmpty ? Comparator.comparingInt(Path::getNodeCount)
+            : Comparator.comparingDouble(Path::getDistToTarget).thenComparingInt(Path::getNodeCount);
+        for (Map.Entry<Target, BlockPos> entry : entryListIsEmpty ? positions : entryList) {
+            Path path = this.reconstructPath(entry.getKey().getBestNode(), entry.getValue(), !entryListIsEmpty);
+            if (best == null || comparator.compare(path, best) < 0)
+                best = path;
+        }
         profilerFiller.pop();
-        return optional.isEmpty() ? null : optional.get();
+        return best;
+        // Paper end - Perf: remove streams and optimize collection
     }
 
     protected float distance(Node a, Node b) {
         return a.distanceTo(b);
     }
 
-    private float getBestH(Node node, Set<Target> targets) {
+    private float getBestH(Node node, List<Map.Entry<Target, BlockPos>> targets) { // Paper - Perf: remove streams and optimize collection; Set<Target> -> List<Map.Entry<Target, BlockPos>>
         float f = Float.MAX_VALUE;
 
-        for (Target target : targets) {
+        // Paper start - Perf: remove streams and optimize collection
+        for (int i = 0, targetsSize = targets.size(); i < targetsSize; i++) {
+            final Target target = targets.get(i).getKey();
+            // Paper end - Perf: remove streams and optimize collection
             float g = node.distanceTo(target);
             target.updateBest(g, node);
             f = Math.min(g, f);