Method initialize

src/log/catchup.cpp:196–206

protected:
  void initialize() override
  {
    // Stop when no one cares.
    promise.future().onDiscard(lambda::bind(
        static_cast<void(*)(const UPID&, bool)>(terminate), self(), true));

    // Catch-up sequentially.
    current = positions.lower();

    catchup();
  }

  void finalize() override
  {