        self_t& concurrency(std::uint16_t concurrency)
        {
            if (concurrency < 2) // Crow can have a minimum of 2 threads running
                concurrency = 2;
            concurrency_ = concurrency;
            return *this;
        }
        self_t& concurrency(std::uint16_t concurrency)
        {
            if (concurrency < 2)  
                concurrency = 2;
            concurrency_ = concurrency;
            return *this;
        }