private static readonly HttpClient client = new HttpClient
{
    Timeout = TimeSpan.FromSeconds(15) // 設(shè)置超時(shí)時(shí)間
};

// 摘要:
//     Gets or sets the maximum number of concurrent connections allowed by a System.Net.ServicePoint
//     object.
//
// 返回結(jié)果:
//     The maximum number of concurrent connections allowed by a System.Net.ServicePoint
//     object. The default connection limit is 10 for ASP.NET hosted applications and
//     2 for all others. When an app is running as an ASP.NET host, it is not possible
//     to alter the value of this property through the config file if the autoConfig
//     property is set to true. However, you can change the value programmatically when
//     the autoConfig property is true. Set your preferred value once, when the AppDomain
//     loads.
//
// 異常:
//   T:System.ArgumentOutOfRangeException:
//     System.Net.ServicePointManager.DefaultConnectionLimit is less than or equal to
//     0.

ServicePointManager.DefaultConnectionLimit = 100; // 調(diào)高默認(rèn)連接限制

HttpResponseMessage response = await client.PostAsync(url, content);

public async Task<string> PostFormResult(string url, string parm)
{
    Log("PostFormResult 開(kāi)始請(qǐng)求: " + url + ", parm: " + parm);
    try
    {
        byte[] buf = Encoding.UTF8.GetBytes(parm);
        using (HttpContent content = new ByteArrayContent(buf))
        {
        	//這里我是表單，可以換成json
            content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/x-www-form-urlencoded");
			//content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
			//添加Token	
		    //client.DefaultRequestHeaders.Add("Authorization", "Bearer " + token);

            HttpResponseMessage res = await client.PostAsync(url, content);

            if (res.IsSuccessStatusCode)
            {
                string json = await res.Content.ReadAsStringAsync();
                Log("PostFormResult請(qǐng)求成功: " + json);
                return json;
            }
            else
            {
                Warning("PostFormResult請(qǐng)求失敗: " + res.StatusCode);
            }
        }

    }
    catch (HttpRequestException ex)
	{
	    Warning("請(qǐng)求Post出現(xiàn)錯(cuò)誤: " + ex.Message);
	}
	catch (Exception ex)
	{
	    Warning($"請(qǐng)求Post出現(xiàn)錯(cuò)誤: {ex.Message}");
	}
    return string.Empty;
}