static <A> AutoCloseable tempSetThreadLocalIfNecessary_weakRef(ThreadLocal<WeakReference> tl, A a) {
  if (tl == null) null;
  WeakReference prev = tl.get();
  if (eq(getWeakRef(prev), a)) null;
  tl.set(weakRef(a));
  ret autoCloseable { tl.set(prev); };
}