Paper/Spigot-Server-Patches/0540-Fix-Concurrency-issue-in-WeightedList.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
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/server/WeightedList.java b/src/main/java/net/minecraft/server/WeightedList.java
index 73e5969b2a15f1639b6285286820e9f7871c7db8..b4e871140e7a0ab5e402e415ea4ff04605157d54 100644
--- a/src/main/java/net/minecraft/server/WeightedList.java
+++ b/src/main/java/net/minecraft/server/WeightedList.java
@@ -14,7 +14,7 @@ import java.util.stream.Stream;
 
 public class WeightedList<U> {
 
-    protected final List<WeightedList.a<U>> a;
+    protected final List<WeightedList.a<U>> list; // Paper - decompile conflict
     private final Random b;
 
     public WeightedList() {
@@ -23,17 +23,17 @@ public class WeightedList<U> {
 
     private WeightedList(List<WeightedList.a<U>> list) {
         this.b = new Random();
-        this.a = Lists.newArrayList(list);
+        this.list = Lists.newArrayList(list); // Paper - decompile conflict
     }
 
     public static <U> Codec<WeightedList<U>> a(Codec<U> codec) {
-        return WeightedList.a.a(codec).listOf().xmap(WeightedList::new, (weightedlist) -> {
-            return weightedlist.a;
+        return WeightedList.a.a(codec).listOf().xmap(WeightedList::new, (weightedlist) -> { // Paper - decompile conflict
+            return weightedlist.list; // Paper - decompile conflict
         });
     }
 
     public WeightedList<U> a(U u0, int i) {
-        this.a.add(new WeightedList.a<>(u0, i));
+        this.list.add(new WeightedList.a<>(u0, i)); // Paper - decompile conflict
         return this;
     }
 
@@ -42,21 +42,20 @@ public class WeightedList<U> {
     }
 
     public WeightedList<U> a(Random random) {
-        this.a.forEach((weightedlist_a) -> {
-            weightedlist_a.a(random.nextFloat());
-        });
-        this.a.sort(Comparator.comparingDouble((object) -> {
-            return ((WeightedList.a) object).c();
-        }));
-        return this;
+        // Paper start - make concurrent safe, work off a clone of the list
+        java.util.ArrayList<WeightedList.a<U>> list = new java.util.ArrayList<WeightedList.a<U>>(this.list);
+        list.forEach((weightedlist_a) -> weightedlist_a.a(random.nextFloat()));
+        list.sort(Comparator.comparingDouble(a::c));
+        return new WeightedList<>(list);
+        // Paper end
     }
 
     public boolean b() {
-        return this.a.isEmpty();
+        return this.list.isEmpty(); // Paper - decompile conflict
     }
 
     public Stream<U> c() {
-        return this.a.stream().map(WeightedList.a::a);
+        return this.list.stream().map(WeightedList.a::a); // Paper - decompile conflict
     }
 
     public U b(Random random) {
@@ -64,7 +63,7 @@ public class WeightedList<U> {
     }
 
     public String toString() {
-        return "WeightedList[" + this.a + "]";
+        return "WeightedList[" + this.list + "]"; // Paper - decompile conflict
     }
 
     public static class a<T> {
@@ -98,11 +97,7 @@ public class WeightedList<U> {
             return new Codec<WeightedList.a<E>>() {
                 public <T> DataResult<Pair<WeightedList.a<E>, T>> decode(DynamicOps<T> dynamicops, T t0) {
                     Dynamic<T> dynamic = new Dynamic(dynamicops, t0);
-                    OptionalDynamic optionaldynamic = dynamic.get("data");
-                    Codec codec1 = codec;
-
-                    codec.getClass();
-                    return optionaldynamic.flatMap(codec1::parse).map((object) -> {
+                    return dynamic.get("data").flatMap(codec::parse).map((object) -> { // Paper - decompile error
                         return new WeightedList.a<>(object, dynamic.get("weight").asInt(1));
                     }).map((weightedlist_a) -> {
                         return Pair.of(weightedlist_a, dynamicops.empty());