PingUrl 的异步版本

    static void Main(string[] args)
    {
        string url = "www.stackoverflow.com";
        var pingTask = PingUrlAsync(url);
        Console.WriteLine($"Waiting for response from {url}");
        Task.WaitAll(pingTask);            
        Console.WriteLine(pingTask.Result);
    }

    static async Task<string> PingUrlAsync(string url)
    {
        string response = string.Empty;
        var ping = new System.Net.NetworkInformation.Ping();

        var result = await ping.SendPingAsync(url);

        await Task.Delay(5000); //simulate slow internet

        if (result.Status == System.Net.NetworkInformation.IPStatus.Success)
        {
            response = $"{url} is online";
        }

        return response;
    }