Fix CME in BiomeDictionary.Type

Thanks @Asek3 for noticing this

Author: embeddedt

forge/src/main/java/org/embeddedt/modernfix/forge/mixin/bugfix/biome_dictionary_cme/BiomeDictionaryTypeMixin.java

@@ -0,0 +1,30 @@
+package org.embeddedt.modernfix.forge.mixin.bugfix.biome_dictionary_cme;
+
+import net.minecraftforge.common.BiomeDictionary;
+import org.objectweb.asm.Opcodes;
+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.Redirect;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentSkipListMap;
+
+@Mixin(value = BiomeDictionary.Type.class, remap = false)
+public class BiomeDictionaryTypeMixin {
+    @Shadow
+    @Mutable
+    @Final
+    private static Map<String, BiomeDictionary.Type> byName;
+
+    /**
+     * @author embeddedt
+     * @reason Biome types are created concurrently so the backing map needs to be thread-safe
+     */
+    @Redirect(method = "<clinit>", at = @At(value = "FIELD", target = "Lnet/minecraftforge/common/BiomeDictionary$Type;byName:Ljava/util/Map;", opcode = Opcodes.PUTSTATIC))
+    private static void useConcurrentMap(Map<String, BiomeDictionary.Type> treeMap) {
+        byName = new ConcurrentSkipListMap<>();
+    }
+}