1 files changed, 69 insertions, 0 deletions
diff --git a/patches/server/0508-Fix-Concurrency-issue-in-WeightedList.patch b/patches/server/0508-Fix-Concurrency-issue-in-WeightedList.patch
new file mode 100644
index 0000000000..4f6d7689d1
--- /dev/null
+++ b/patches/server/0508-Fix-Concurrency-issue-in-WeightedList.patch
@@ -0,0 +1,69 @@
+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 WeightedList
+
+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 c1f22c5e17418f91736237af1495a8a9910a61d5..e644bdd3a6f7c09a44149da03587b796674fa568 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
+@@ -16,7 +16,7 @@ public class GateBehavior<E extends LivingEntity> extends Behavior<E> {
+     private final Set<MemoryModuleType<?>> exitErasedMemories;
+     private final GateBehavior.OrderPolicy orderPolicy;
+     private final GateBehavior.RunningPolicy runningPolicy;
+-    private final ShufflingList<Behavior<? super E>> behaviors = new ShufflingList<>();
++    private final ShufflingList<Behavior<? super E>> behaviors = new ShufflingList<>(false); // Paper  - don't use a clone
+ 
+     public GateBehavior(Map<MemoryModuleType<?>, MemoryStatus> requiredMemoryState, Set<MemoryModuleType<?>> memoriesToForgetWhenStopped, GateBehavior.OrderPolicy order, GateBehavior.RunningPolicy runMode, List<Pair<Behavior<? super E>, Integer>> tasks) {
+         super(requiredMemoryState);
+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 ca4c067ae99f4a1f2e62f8d92928d65ab29bc517..1bc34453933bc7590af45a5559a4fc75eb3e0c5c 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
+@@ -14,12 +14,25 @@ import java.util.stream.Stream;
+ public class ShufflingList<U> {
+     protected final List<ShufflingList.WeightedEntry<U>> entries;
+     private final Random random = new Random();
++    private final boolean isUnsafe; // Paper
+ 
+     public ShufflingList() {
++        // Paper start
++        this(true);
++    }
++    public ShufflingList(boolean isUnsafe) {
++        this.isUnsafe = isUnsafe;
++        // Paper end
+         this.entries = Lists.newArrayList();
+     }
+ 
+     private ShufflingList(List<ShufflingList.WeightedEntry<U>> list) {
++        // Paper start
++        this(list, true);
++    }
++    private ShufflingList(List<ShufflingList.WeightedEntry<U>> list, boolean isUnsafe) {
++        this.isUnsafe = isUnsafe;
++        // Paper end
+         this.entries = Lists.newArrayList(list);
+     }
+ 
+@@ -35,11 +48,12 @@ public class ShufflingList<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 - make concurrent safe, work off a clone of the list
++        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
+     }
+ 
+     public Stream<U> stream() {