Fix MC-218112

src/main/java/org/embeddedt/modernfix/core/config/ModernFixEarlyConfig.java

@@ -36,6 +36,7 @@ public class ModernFixEarlyConfig {
         this.addMixinRule("bugfix.edge_chunk_not_saved", true);
         this.addMixinRule("bugfix.packet_leak", false);
         this.addMixinRule("bugfix.structure_manager_crash", true);
+        this.addMixinRule("bugfix.mc218112", true);
         this.addMixinRule("perf.async_jei", true);
         this.addMixinRule("perf.thread_priorities", true);
         this.addMixinRule("perf.preload_block_classes", false);

src/main/java/org/embeddedt/modernfix/mixin/bugfix/mc218112/SynchedEntityDataMixin.java

@@ -0,0 +1,34 @@
+package org.embeddedt.modernfix.mixin.bugfix.mc218112;
+
+import net.minecraft.network.syncher.EntityDataAccessor;
+import net.minecraft.network.syncher.SynchedEntityData;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+import org.spongepowered.asm.mixin.injection.callback.LocalCapture;
+
+import java.util.Map;
+import java.util.concurrent.locks.ReadWriteLock;
+
+@Mixin(SynchedEntityData.class)
+public class SynchedEntityDataMixin {
+    @Shadow @Final private Map<Integer, SynchedEntityData.DataItem<?>> itemsById;
+
+    @Shadow @Final private ReadWriteLock lock;
+
+    @Shadow private boolean isEmpty;
+
+    @Inject(method = "createDataItem", at = @At(value = "INVOKE", target = "Ljava/util/Map;put(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;"), cancellable = true, locals = LocalCapture.CAPTURE_FAILHARD)
+    private <T> void putWithLock(EntityDataAccessor<T> key, T value, CallbackInfo ci, SynchedEntityData.DataItem<T> item) {
+        ci.cancel();
+        try {
+            this.itemsById.put(key.getId(), item);
+            this.isEmpty = false;
+        } finally {
+            this.lock.writeLock().unlock();
+        }
+    }
+}

src/main/java/org/embeddedt/modernfix/mixin/bugfix/mc218112/SynchedEntityDataMixin_Client.java

@@ -0,0 +1,46 @@
+package org.embeddedt.modernfix.mixin.bugfix.mc218112;
+
+import net.minecraft.network.syncher.SynchedEntityData;
+import net.minecraft.world.entity.Entity;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Overwrite;
+import org.spongepowered.asm.mixin.Shadow;
+
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.locks.ReadWriteLock;
+
+@Mixin(SynchedEntityData.class)
+public abstract class SynchedEntityDataMixin_Client {
+    @Shadow @Final private ReadWriteLock lock;
+
+    @Shadow private boolean isDirty;
+
+    @Shadow protected abstract <T> void assignValue(SynchedEntityData.DataItem<T> target, SynchedEntityData.DataItem<?> source);
+
+    @Shadow @Final private Entity entity;
+
+    @Shadow @Final private Map<Integer, SynchedEntityData.DataItem<?>> itemsById;
+
+    /**
+     * @author embeddedt
+     * @reason always unlock
+     */
+    @Overwrite
+    public void assignValues(List<SynchedEntityData.DataItem<?>> entries) {
+        this.lock.writeLock().lock();
+        try {
+            for(SynchedEntityData.DataItem<?> dataentry : entries) {
+                SynchedEntityData.DataItem<?> dataentry1 = this.itemsById.get(dataentry.getAccessor().getId());
+                if (dataentry1 != null) {
+                    this.assignValue(dataentry1, dataentry);
+                    this.entity.onSyncedDataUpdated(dataentry.getAccessor());
+                }
+            }
+        } finally {
+            this.lock.writeLock().unlock();
+        }
+        this.isDirty = true;
+    }
+}

src/main/resources/modernfix.mixins.json

@@ -52,6 +52,7 @@
     "perf.fast_registry_validation.ForgeRegistryMixin",
     "perf.cache_strongholds.ChunkGeneratorMixin",
     "perf.cache_upgraded_structures.StructureManagerMixin",
+    "bugfix.mc218112.SynchedEntityDataMixin",
     "perf.cache_strongholds.ServerLevelMixin"
   ],
   "client": [
@@ -94,6 +95,7 @@
     "perf.reuse_datapacks.MinecraftServerMixin",
     "perf.use_integrated_resources.LootTableHelperMixin",
     "perf.use_integrated_resources.PiglinBarteringRecipeBuilderMixin",
+    "bugfix.mc218112.SynchedEntityDataMixin_Client",
     "perf.faster_singleplayer_load.MinecraftServerMixin"
   ],
   "injectors": {