fix MC-271899

PATCHED.md

@@ -62,6 +62,7 @@
 | Basic    | [MC-224729](https://bugs.mojang.com/browse/MC-224729) | Partially generated chunks are not saved in some situations                                                                                    |
 | Basic    | [MC-231743](https://bugs.mojang.com/browse/MC-231743) | minecraft.used:minecraft.POTTABLE_PLANT doesn't increase when placing plants into flower pots                                                  |
 | Basic    | [MC-232869](https://bugs.mojang.com/browse/MC-232869) | Adult striders can spawn with saddles in peaceful mode                                                                                         |
+| Basic    | [MC-271899](https://bugs.mojang.com/browse/MC-271899) | StructureTemplate Palette's caches are not thread safe                                                                                         |
 
 ## Previously patched
 Bugs that this mod has patched but has been superseded by a vanilla update.

src/main/java/dev/isxander/debugify/mixins/basic/mc271899/StructureTemplateMixin.java

@@ -0,0 +1,31 @@
+package dev.isxander.debugify.mixins.basic.mc271899;
+
+import com.google.common.collect.Maps;
+import dev.isxander.debugify.fixes.BugFix;
+import dev.isxander.debugify.fixes.FixCategory;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.levelgen.structure.templatesystem.StructureTemplate;
+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.List;
+import java.util.Map;
+
+@BugFix(id = "MC-271899", category = FixCategory.BASIC, env = BugFix.Env.SERVER, description = "StructureTemplate Palette's caches are not thread safe")
+@Mixin(StructureTemplate.Palette.class)
+public class StructureTemplateMixin {
+    @Mutable
+    @Shadow
+    @Final
+    private Map<Block, List<StructureTemplate.StructureBlockInfo>> cache;
+
+    @Inject(method = "<init>", at = @At(value = "TAIL"))
+    private void newHashMap(List list, CallbackInfo ci) {
+        this.cache = Maps.newConcurrentMap();
+    }
+}

src/main/resources/debugify.mixins.json

@@ -30,6 +30,7 @@
     "basic.mc224729.ChunkMapMixin",
     "basic.mc231743.FlowerPotBlockMixin",
     "basic.mc232869.StriderMixin",
+    "basic.mc271899.StructureTemplateMixin",
     "basic.mc30391.LivingEntityMixin",
     "basic.mc69216.ServerPlayerMixin",
     "basic.mc7569.RconConsoleSourceMixin",