Make backing maps in ItemProperties thread-safe

Helps prevent CMEs on Forge 1.16

Author: embeddedt

common/src/main/java/org/embeddedt/modernfix/common/mixin/safety/ItemPropertiesMixin.java

@@ -0,0 +1,30 @@
+package org.embeddedt.modernfix.common.mixin.safety;
+
+import net.minecraft.client.renderer.item.ItemProperties;
+import net.minecraft.client.renderer.item.ItemPropertyFunction;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.item.Item;
+import org.embeddedt.modernfix.annotation.ClientOnlyMixin;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Mutable;
+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 java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+@Mixin(value = ItemProperties.class, priority = 700)
+@ClientOnlyMixin
+public class ItemPropertiesMixin {
+    @Shadow @Final @Mutable private static Map<ResourceLocation, ItemPropertyFunction> GENERIC_PROPERTIES;
+    @Shadow @Final @Mutable private static Map<Item, Map<ResourceLocation, ItemPropertyFunction>> PROPERTIES;
+
+    @Inject(method = "<clinit>", at = @At("RETURN"))
+    private static void useConcurrentMaps(CallbackInfo ci) {
+        GENERIC_PROPERTIES = new ConcurrentHashMap<>(GENERIC_PROPERTIES);
+        PROPERTIES = new ConcurrentHashMap<>(PROPERTIES);
+    }
+}