void set_lock_held() { lock_held_ = true; }

  // Returns true if the resource variable reader lock was successfully acquired
  // by this thread.
  bool shared_lock_held() const { return shared_lock_held_; }
  void set_shared_lock_held() { shared_lock_held_ = true; }

  bool read_only() const { return read_only_; }
  void set_read_only() { read_only_ = true; }

  const std::optional<ManagedStackTrace>& definition_stack_trace() const {

    }
    if (variables[i]->read_only()) {
      VLOG(4) << "Acquiring reader lock for variable "
              << reinterpret_cast<void*>(variable);
      mu->lock_shared();
      variables[i]->set_shared_lock_held();
    } else {
      VLOG(4) << "Acquiring lock for variable "
              << reinterpret_cast<void*>(variable);
      mu->lock();
      variables[i]->set_lock_held();
    }
    prev = mu;
  }