1 files changed, 67 insertions, 0 deletions
diff --git a/patches/server/0418-Fix-Concurrency-issue-in-ShufflingList.patch b/patches/server/0418-Fix-Concurrency-issue-in-ShufflingList.patch
new file mode 100644
index 0000000000..f04a40e1ac
--- /dev/null
+++ b/patches/server/0418-Fix-Concurrency-issue-in-ShufflingList.patch
@@ -0,0 +1,67 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aikar <[email protected]>
+Date: Mon, 6 Jul 2020 18:36:41 -0400
+Subject: [PATCH] Fix Concurrency issue in ShufflingList
+
+if multiple threads from worldgen sort at same time, it will crash.
+So make a copy of the list for sorting purposes.
+
+diff --git a/src/main/java/net/minecraft/world/entity/ai/behavior/GateBehavior.java b/src/main/java/net/minecraft/world/entity/ai/behavior/GateBehavior.java
+index 334962f1bf5988059fec506f0d3aaf4302205220..6a270c9adb044a6e0b1c8e09b9106d51989fd761 100644
+--- a/src/main/java/net/minecraft/world/entity/ai/behavior/GateBehavior.java
++++ b/src/main/java/net/minecraft/world/entity/ai/behavior/GateBehavior.java
+@@ -18,7 +18,7 @@ public class GateBehavior<E extends LivingEntity> implements BehaviorControl<E>
+     private final Set<MemoryModuleType<?>> exitErasedMemories;
+     private final GateBehavior.OrderPolicy orderPolicy;
+     private final GateBehavior.RunningPolicy runningPolicy;
+-    private final ShufflingList<BehaviorControl<? super E>> behaviors = new ShufflingList<>();
++    private final ShufflingList<BehaviorControl<? super E>> behaviors = new ShufflingList<>(false); // Paper - Fix Concurrency issue in ShufflingList during worldgen
+     private Behavior.Status status = Behavior.Status.STOPPED;
+ 
+     public GateBehavior(
+diff --git a/src/main/java/net/minecraft/world/entity/ai/behavior/ShufflingList.java b/src/main/java/net/minecraft/world/entity/ai/behavior/ShufflingList.java
+index 195eea55fabc7a9a665e0a8f04934a3aaf9f8b71..3fac11bf02652b5f51f30f99bdf516504467d0d2 100644
+--- a/src/main/java/net/minecraft/world/entity/ai/behavior/ShufflingList.java
++++ b/src/main/java/net/minecraft/world/entity/ai/behavior/ShufflingList.java
+@@ -16,12 +16,25 @@ import net.minecraft.util.RandomSource;
+ public class ShufflingList<U> implements Iterable<U> {
+     protected final List<ShufflingList.WeightedEntry<U>> entries;
+     private final RandomSource random = RandomSource.create();
++    private final boolean isUnsafe; // Paper - Fix Concurrency issue in ShufflingList during worldgen
+ 
+     public ShufflingList() {
++        // Paper start - Fix Concurrency issue in ShufflingList during worldgen
++        this(true);
++    }
++    public ShufflingList(boolean isUnsafe) {
++        this.isUnsafe = isUnsafe;
++        // Paper end - Fix Concurrency issue in ShufflingList during worldgen
+         this.entries = Lists.newArrayList();
+     }
+ 
+     private ShufflingList(List<ShufflingList.WeightedEntry<U>> list) {
++        // Paper start - Fix Concurrency issue in ShufflingList during worldgen
++        this(list, true);
++    }
++    private ShufflingList(List<ShufflingList.WeightedEntry<U>> list, boolean isUnsafe) {
++        this.isUnsafe = isUnsafe;
++        // Paper end - Fix Concurrency issue in ShufflingList during worldgen
+         this.entries = Lists.newArrayList(list);
+     }
+ 
+@@ -35,9 +48,12 @@ public class ShufflingList<U> implements Iterable<U> {
+     }
+ 
+     public ShufflingList<U> shuffle() {
+-        this.entries.forEach(entry -> entry.setRandom(this.random.nextFloat()));
+-        this.entries.sort(Comparator.comparingDouble(ShufflingList.WeightedEntry::getRandWeight));
+-        return this;
++        // Paper start - Fix Concurrency issue in ShufflingList during worldgen
++        List<ShufflingList.WeightedEntry<U>> list = this.isUnsafe ? Lists.newArrayList(this.entries) : this.entries;
++        list.forEach(entry -> entry.setRandom(this.random.nextFloat()));
++        list.sort(Comparator.comparingDouble(ShufflingList.WeightedEntry::getRandWeight));
++        return this.isUnsafe ? new ShufflingList<>(list, this.isUnsafe) : this;
++        // Paper end - Fix Concurrency issue in ShufflingList during worldgen
+     }
+ 
+     public Stream<U> stream() {