From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Mon, 15 May 2023 00:20:59 -0700
Subject: [PATCH] Fix concurrenct access to lookups field in RegistryOps

The concurrent access occurs on the Netty IO threads when
serializing packets. Thus, it seems it was an oversight of
the implementator of this function as there are typically
more than one Netty IO thread.

Fixes https://github.com/PaperMC/Folia/issues/11

diff --git a/src/main/java/net/minecraft/resources/RegistryOps.java b/src/main/java/net/minecraft/resources/RegistryOps.java
index e682e40b2c82c6d47dcaa6a3ff56a2e1f14f422f..1722c88c93cf8a09a9acb37e838b137c0e5cde64 100644
--- a/src/main/java/net/minecraft/resources/RegistryOps.java
+++ b/src/main/java/net/minecraft/resources/RegistryOps.java
@@ -19,11 +19,11 @@ public class RegistryOps<T> extends DelegatingOps<T> {
 
     private static RegistryOps.RegistryInfoLookup memoizeLookup(final RegistryOps.RegistryInfoLookup registryInfoGetter) {
         return new RegistryOps.RegistryInfoLookup() {
-            private final Map<ResourceKey<? extends Registry<?>>, Optional<? extends RegistryOps.RegistryInfo<?>>> lookups = new HashMap<>();
+            private final Map<ResourceKey<? extends Registry<?>>, Optional<? extends RegistryOps.RegistryInfo<?>>> lookups = new java.util.concurrent.ConcurrentHashMap<>(); // Paper - fix concurrent access to lookups field
 
             @Override
             public <T> Optional<RegistryOps.RegistryInfo<T>> lookup(ResourceKey<? extends Registry<? extends T>> registryRef) {
-                return this.lookups.computeIfAbsent(registryRef, registryInfoGetter::lookup);
+                return (Optional<RegistryOps.RegistryInfo<T>>)this.lookups.computeIfAbsent(registryRef, registryInfoGetter::lookup); // Paper - fix concurrent access to lookups field
             }
         };
     }