From 5a79c151ef16461c449db1fb33918b3730ca2a7f Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Mon, 23 Jul 2018 19:13:06 -0400
Subject: [PATCH] Thread Safe Iteration of Chunk Scheduler


diff --git a/src/main/java/net/minecraft/server/ChunkTaskScheduler.java b/src/main/java/net/minecraft/server/ChunkTaskScheduler.java
index 7629e0d05..5ee8bedf3 100644
--- a/src/main/java/net/minecraft/server/ChunkTaskScheduler.java
+++ b/src/main/java/net/minecraft/server/ChunkTaskScheduler.java
@@ -1,8 +1,10 @@
 package net.minecraft.server;
 
+import com.google.common.collect.Lists;
 import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
 import it.unimi.dsi.fastutil.longs.Long2ObjectMaps;
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.EnumMap;
 import java.util.Map;
 import java.util.function.Consumer;
@@ -85,7 +87,13 @@ public class ChunkTaskScheduler extends Scheduler<ChunkCoordIntPair, ChunkStatus
     }
 
     public void a() {
-        this.g.values().forEach((scheduler_a) -> {
+        // Paper start
+        ArrayList<Scheduler.a> list;
+        synchronized (this.g) {
+            list = Lists.newArrayList(this.g.values());
+        }
+        list.forEach((scheduler_a) -> {
+            // Paper end
             ProtoChunk protochunk = (ProtoChunk) scheduler_a.a();
 
             if (protochunk.h() && protochunk.i().d() == ChunkStatus.Type.PROTOCHUNK) {
@@ -93,6 +101,7 @@ public class ChunkTaskScheduler extends Scheduler<ChunkCoordIntPair, ChunkStatus
                     protochunk.setLastSaved(this.c.getTime());
                     this.e.saveChunk(this.c, protochunk);
                     protochunk.a(false);
+
                 } catch (IOException ioexception) {
                     ChunkTaskScheduler.b.error("Couldn\'t save chunk", ioexception);
                 } catch (ExceptionWorldConflict exceptionworldconflict) {
-- 
2.18.0