Paper/nms-patches/ChunkGenerator.patch

--- a/net/minecraft/server/ChunkGenerator.java
+++ b/net/minecraft/server/ChunkGenerator.java
@@ -214,6 +214,13 @@
         while (iterator.hasNext()) {
             StructureFeature<?, ?> structurefeature = (StructureFeature) iterator.next();
 
+            // CraftBukkit start
+            if (structurefeature.b == StructureGenerator.STRONGHOLD) {
+                synchronized (structurefeature) {
+                    this.a(structurefeature, structuremanager, ichunkaccess, definedstructuremanager, i, chunkcoordintpair, biomebase);
+                }
+            } else
+            // CraftBukkit end
             this.a(structurefeature, structuremanager, ichunkaccess, definedstructuremanager, i, chunkcoordintpair, biomebase);
         }
 
@@ -293,9 +300,11 @@
     }
 
     static {
-        IRegistry.a(IRegistry.CHUNK_GENERATOR, "noise", (Object) ChunkGeneratorAbstract.d);
-        IRegistry.a(IRegistry.CHUNK_GENERATOR, "flat", (Object) ChunkProviderFlat.d);
-        IRegistry.a(IRegistry.CHUNK_GENERATOR, "debug", (Object) ChunkProviderDebug.e);
+        // CraftBukkit start - decompile errors
+        IRegistry.a(IRegistry.CHUNK_GENERATOR, "noise", ChunkGeneratorAbstract.d);
+        IRegistry.a(IRegistry.CHUNK_GENERATOR, "flat", ChunkProviderFlat.d);
+        IRegistry.a(IRegistry.CHUNK_GENERATOR, "debug", ChunkProviderDebug.e);
+        // CraftBukkit end
         a = IRegistry.CHUNK_GENERATOR.dispatchStable(ChunkGenerator::a, Function.identity());
     }
 }