// spawn enough connections to satisfy open requests and minpool, while honoring maxpool
void ConnectionPool::SpecificPool::spawnConnections() {
    ...
    for (decltype(allowance) i = 0; i < allowance; ++i) {
        OwnedConnection handle;
        try {
            handle = _parent->_factory->makeConnection(_hostAndPort, _sslMode, _generation);
        } catch (std::system_error& e) {
            ...
        }
        ...
        handle->setup(_parent->_controller->pendingTimeout(),
                      guardCallback([this](auto conn, auto status) {
                          finishRefresh(std::move(conn), std::move(status));
                      }),
                      _parent->getName());
    }
}