From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <spottedleaf@spottedleaf.dev>
Date: Thu, 7 May 2020 05:48:54 -0700
Subject: [PATCH] Optimise chunk tick iteration

Use a dedicated list of entity ticking chunks to reduce the cost

diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index b5c8f3f57d09de4caffeb9f3e20e9bf4daba1cdd..d6981bbcf480c5856b51960013d144beba2361b3 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -1007,19 +1007,35 @@ public class ServerChunkCache extends ChunkSource {
 
             this.lastSpawnState = spawnercreature_d;
             this.level.getProfiler().pop();
-            List<ChunkHolder> list = Lists.newArrayList(this.chunkMap.getChunks());
-
-            Collections.shuffle(list);
+            // Paper - moved down, enabled if per-player = false
             // Paper - moved natural spawn event up
             this.level.timings.chunkTicks.startTiming(); // Paper
-            list.forEach((playerchunk) -> {
-                Optional<LevelChunk> optional = ((Either) playerchunk.getTickingChunkFuture().getNow(ChunkHolder.UNLOADED_LEVEL_CHUNK)).left();
-
-                if (optional.isPresent()) {
-                    LevelChunk chunk = (LevelChunk) optional.get();
+            // Paper start
+            java.util.Iterator<LevelChunk> iterator;
+            if (this.level.paperConfig.perPlayerMobSpawns) {
+                iterator = this.entityTickingChunks.iterator();
+            } else {
+                iterator = this.entityTickingChunks.unsafeIterator();
+                List<LevelChunk> shuffled = new java.util.ArrayList<>(this.entityTickingChunks.size());
+                while (iterator.hasNext()) {
+                    shuffled.add(iterator.next());
+                }
+                Collections.shuffle(shuffled);
+                iterator = shuffled.iterator();
+            }
+            try { while (iterator.hasNext()) {
+                LevelChunk chunk = iterator.next();
+                ChunkHolder playerchunk = chunk.playerChunk;
+                if (playerchunk != null) {
+                    this.level.getProfiler().push("broadcast");
+                    this.level.timings.broadcastChunkUpdates.startTiming(); // Paper - timings
+                    playerchunk.broadcastChanges(chunk);
+                    this.level.timings.broadcastChunkUpdates.stopTiming(); // Paper - timings
+                    this.level.getProfiler().pop();
+                    // Paper end
                     ChunkPos chunkcoordintpair = chunk.getPos();
 
-                    if (this.level.isPositionEntityTicking(chunkcoordintpair) && !this.chunkMap.isOutsideOfRange(playerchunk, chunkcoordintpair, false)) { // Paper - optimise isOutsideOfRange
+                    if ((true || this.level.isPositionEntityTicking(chunkcoordintpair)) && !this.chunkMap.isOutsideOfRange(playerchunk, chunkcoordintpair, false)) { // Paper - optimise isOutsideOfRange // Paper - we only iterate entity ticking chunks
                         chunk.setInhabitedTime(chunk.getInhabitedTime() + j);
                         if (flag1 && (this.spawnEnemies || this.spawnFriendlies) && this.level.getWorldBorder().isWithinBounds(chunk.getPos()) && !this.chunkMap.isOutsideOfRange(playerchunk, chunkcoordintpair, true)) { // Spigot // Paper - optimise isOutsideOfRange
                             NaturalSpawner.spawnForChunk(this.level, chunk, spawnercreature_d, this.spawnFriendlies, this.spawnEnemies, flag2);
@@ -1030,7 +1046,13 @@ public class ServerChunkCache extends ChunkSource {
                         // this.level.timings.doTickTiles.stopTiming(); // Spigot // Paper
                     }
                 }
-            });
+            } // Paper start - optimise chunk tick iteration
+            } finally {
+                if (iterator instanceof io.papermc.paper.util.maplist.IteratorSafeOrderedReferenceSet.Iterator) {
+                    ((io.papermc.paper.util.maplist.IteratorSafeOrderedReferenceSet.Iterator<LevelChunk>)iterator).finishedIterating();
+                }
+            }
+            // Paper end - optimise chunk tick iteration
             this.level.timings.chunkTicks.stopTiming(); // Paper
             this.level.getProfiler().push("customSpawners");
             if (flag1) {
@@ -1039,21 +1061,7 @@ public class ServerChunkCache extends ChunkSource {
                 } // Paper - timings
             }
 
-            this.level.getProfiler().popPush("broadcast");
-            this.chunkMap.getChunks().forEach((playerchunk) -> { // Paper - no... just no...
-                Optional<LevelChunk> optional = ((Either) playerchunk.getTickingChunkFuture().getNow(ChunkHolder.UNLOADED_LEVEL_CHUNK)).left(); // CraftBukkit - decompile error
-
-                Objects.requireNonNull(playerchunk);
-
-                // Paper start - timings
-                optional.ifPresent(chunk -> {
-                    this.level.timings.broadcastChunkUpdates.startTiming(); // Paper - timings
-                    playerchunk.broadcastChanges(chunk);
-                    this.level.timings.broadcastChunkUpdates.stopTiming(); // Paper - timings
-                });
-                // Paper end
-            });
-            this.level.getProfiler().pop();
+            // Paper - no, iterating just ONCE is expensive enough! Don't do it TWICE! Code moved up
             this.level.getProfiler().pop();
         }