From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Shane Freeder <theboyetronic@gmail.com>
Date: Wed, 29 May 2019 04:01:22 +0100
Subject: [PATCH] ChunkMapDistance CME


diff --git a/src/main/java/net/minecraft/server/level/ChunkHolder.java b/src/main/java/net/minecraft/server/level/ChunkHolder.java
index 165e72873da877f7a29d58e4da489f68979725ad..ddaf9d682772d5dbbe6ee4891f9995a8ee365329 100644
--- a/src/main/java/net/minecraft/server/level/ChunkHolder.java
+++ b/src/main/java/net/minecraft/server/level/ChunkHolder.java
@@ -73,6 +73,7 @@ public class ChunkHolder {
     private boolean resendLight;
     private CompletableFuture<Void> pendingFullStateConfirmation;
 
+    boolean isUpdateQueued = false; // Paper
     private final ChunkMap chunkMap; // Paper
 
     public ChunkHolder(ChunkPos pos, int level, LevelHeightAccessor world, LevelLightEngine lightingProvider, ChunkHolder.LevelChangeListener levelUpdateListener, ChunkHolder.PlayerProvider playersWatchingChunkProvider) {
diff --git a/src/main/java/net/minecraft/server/level/DistanceManager.java b/src/main/java/net/minecraft/server/level/DistanceManager.java
index 48bb57d3a431ea466425eb7da821c0aea900bd4c..45c7ebe67019cdbe88b6617a95d5c40d3a68286c 100644
--- a/src/main/java/net/minecraft/server/level/DistanceManager.java
+++ b/src/main/java/net/minecraft/server/level/DistanceManager.java
@@ -47,7 +47,16 @@ public abstract class DistanceManager {
     private final DistanceManager.ChunkTicketTracker ticketTracker = new DistanceManager.ChunkTicketTracker();
     private final DistanceManager.FixedPlayerDistanceChunkTracker naturalSpawnChunkCounter = new DistanceManager.FixedPlayerDistanceChunkTracker(8);
     private final DistanceManager.PlayerTicketTracker playerTicketManager = new DistanceManager.PlayerTicketTracker(33);
-    final Set<ChunkHolder> chunksToUpdateFutures = Sets.newHashSet();
+    // Paper start use a queue, but still keep unique requirement
+    public final java.util.Queue<ChunkHolder> pendingChunkUpdates = new java.util.ArrayDeque<ChunkHolder>() {
+        @Override
+        public boolean add(ChunkHolder o) {
+            if (o.isUpdateQueued) return true;
+            o.isUpdateQueued = true;
+            return super.add(o);
+        }
+    };
+    // Paper end
     final ChunkTaskPriorityQueueSorter ticketThrottler;
     final ProcessorHandle<ChunkTaskPriorityQueueSorter.Message<Runnable>> ticketThrottlerInput;
     final ProcessorHandle<ChunkTaskPriorityQueueSorter.Release> ticketThrottlerReleaser;
@@ -108,26 +117,14 @@ public abstract class DistanceManager {
             ;
         }
 
-        if (!this.chunksToUpdateFutures.isEmpty()) {
-            // CraftBukkit start
-            // Iterate pending chunk updates with protection against concurrent modification exceptions
-            java.util.Iterator<ChunkHolder> iter = this.chunksToUpdateFutures.iterator();
-            int expectedSize = this.chunksToUpdateFutures.size();
-            do {
-                ChunkHolder playerchunk = iter.next();
-                iter.remove();
-                expectedSize--;
-
-                playerchunk.updateFutures(playerchunkmap, this.mainThreadExecutor);
-
-                // Reset iterator if set was modified using add()
-                if (this.chunksToUpdateFutures.size() != expectedSize) {
-                    expectedSize = this.chunksToUpdateFutures.size();
-                    iter = this.chunksToUpdateFutures.iterator();
-                }
-            } while (iter.hasNext());
-            // CraftBukkit end
-
+        // Paper start
+        if (!this.pendingChunkUpdates.isEmpty()) {
+            while(!this.pendingChunkUpdates.isEmpty()) {
+                ChunkHolder remove = this.pendingChunkUpdates.remove();
+                remove.isUpdateQueued = false;
+                remove.updateFutures(playerchunkmap, this.mainThreadExecutor);
+            }
+            // Paper end
             return true;
         } else {
             if (!this.ticketsToRelease.isEmpty()) {
@@ -385,7 +382,7 @@ public abstract class DistanceManager {
             if (k != level) {
                 playerchunk = DistanceManager.this.updateChunkScheduling(id, level, playerchunk, k);
                 if (playerchunk != null) {
-                    DistanceManager.this.chunksToUpdateFutures.add(playerchunk);
+                    DistanceManager.this.pendingChunkUpdates.add(playerchunk);
                 }
 
             }