code: public static TStructDescriptor getInstance(Class<? extends TBase<?, ?>> tClass) {
      synchronized (structMap) {
        TStructDescriptor desc = structMap.get(tClass);
        if (desc == null) {
          desc = new TStructDescriptor();
          desc.tClass = tClass;
          structMap.put(tClass, desc);
          desc.build(tClass);
        }
        return desc;
      }
    }
docs: Creates a descriptor for a Thrift class