你可能寫了個假異步，並不能提高請求線程池的吞吐量

不知道用什么詞形容，就叫它假異步吧。

寫異步方法，async 和 await 要一路寫到底，否則就是假異步，並不能提高請求線程池的吞吐量。

真正的異步，我的理解是這樣的：比如調用一個查詢接口，在當前線程，把SQL扔給數據庫，當前線程釋放，去干別的事情，數據庫查詢完了，通知我，我再在另一個線程里(也可能是剛才釋放的那個線程，也可能不是)拿查詢結果，返回給客戶端，數據庫查詢比較耗時，數據庫查詢的時候，對線程是0占用。

 

HttpUtil.HttpGet方法：

/// <summary>
/// HttpGet
/// </summary>
/// <param name="url">url路徑名稱</param>
/// <param name="cookie">cookie</param>
public static string HttpGet(string url, CookieContainer cookie = null, WebHeaderCollection headers = null)
{
    try
    {
        // 設置參數
        HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
        request.CookieContainer = cookie;
        request.Method = "GET";
        request.ContentType = "text/plain;charset=utf-8";

        if (headers != null)
        {
            foreach (string key in headers.Keys)
            {
                request.Headers.Add(key, headers[key]);
            }
        }

        //發送請求並獲取相應回應數據
        HttpWebResponse response = request.GetResponse() as HttpWebResponse;
        //直到request.GetResponse()程序才開始向目標網頁發送Post請求
        Stream instream = response.GetResponseStream();
        StreamReader sr = new StreamReader(instream, Encoding.UTF8);
        //返回結果網頁（html）代碼
        string content = sr.ReadToEnd();
        instream.Close();
        return content;
    }
    catch (Exception ex)
    {
        LogUtil.Error(ex);
        return string.Empty;
    }
}

HttpUtil.HttpGetAsync方法：

/// <summary>
/// HttpGetAsync
/// </summary>
/// <param name="url">url路徑名稱</param>
/// <param name="cookie">cookie</param>
public static async Task<string> HttpGetAsync(string url, CookieContainer cookie = null, WebHeaderCollection headers = null)
{
    try
    {
        // 設置參數
        HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
        request.CookieContainer = cookie;
        request.Method = "GET";
        request.ContentType = "text/plain;charset=utf-8";

        if (headers != null)
        {
            foreach (string key in headers.Keys)
            {
                request.Headers.Add(key, headers[key]);
            }
        }

        //發送請求並獲取相應回應數據
        HttpWebResponse response = await request.GetResponseAsync() as HttpWebResponse;
        //直到request.GetResponse()程序才開始向目標網頁發送Post請求
        Stream instream = response.GetResponseStream();
        StreamReader sr = new StreamReader(instream, Encoding.UTF8);
        //返回結果網頁（html）代碼
        string content = sr.ReadToEnd();
        instream.Close();
        return content;
    }
    catch (Exception ex)
    {
        LogUtil.Error(ex);
        return string.Empty;
    }
}

測試代碼：

/// <summary>
/// 測試1
/// </summary>
private async void button1_Click(object sender, EventArgs e)
{
    //task是自己寫的獨立線程池，為了防止測試過程對CLR線程池和異步線程池造成干擾
    _task.Run(() =>
    {
        Thread.Sleep(200);

        int workerThreads1, completionPortThreads1, workerThreads2, completionPortThreads2;
        ThreadPool.GetMaxThreads(out workerThreads1, out completionPortThreads1);
        ThreadPool.GetAvailableThreads(out workerThreads2, out completionPortThreads2);
        Log("假異步 已使用輔助線程：" + (workerThreads1 - workerThreads2) + ", 已使用異步線程：" + (completionPortThreads1 - completionPortThreads2));
    });

    string str = await GetDataAsync();
}

/// <summary>
/// 測試2 
/// </summary>
private async void button2_Click(object sender, EventArgs e)
{
    //task是自己寫的獨立線程池，為了防止測試過程對CLR線程池和異步線程池造成干擾
    _task.Run(() =>
    {
        Thread.Sleep(200);

        int workerThreads1, completionPortThreads1, workerThreads2, completionPortThreads2;
        ThreadPool.GetMaxThreads(out workerThreads1, out completionPortThreads1);
        ThreadPool.GetAvailableThreads(out workerThreads2, out completionPortThreads2);
        Log("真異步 已使用輔助線程：" + (workerThreads1 - workerThreads2) + ", 已使用異步線程：" + (completionPortThreads1 - completionPortThreads2));
    });

    string str = await GetDataAsync2();
}

/// <summary>
/// 假異步
/// </summary>
private async Task<string> GetDataAsync()
{
    return await Task.Run<string>(() =>
    {
        //接口耗時大約1秒
        return HttpUtil.HttpGet("http://localhost:8500/api/test/TestGet?val=1", null, null);
    });
}

/// <summary>
/// 真異步
/// </summary>
/// <returns></returns>
private async Task<string> GetDataAsync2()
{
    //接口耗時大約1秒
    return await HttpUtil.HttpGetAsync("http://localhost:8500/api/test/TestGet?val=1", null, null);
}

測試截圖：

我想知道 WebRequest 類的 GetResponseAsync 方法是怎么實現的，反正使用.NET提供的類，我是無法實現這樣的方法。

這篇隨筆如果有錯誤，請指正，我只是拋磚引玉，提出疑問或者說假設。

async await 要一路寫到底啊，重構壓力真大。

如果在異步方法中調用同步方法，又不想占用CLR線程池的線程，可以把耗時操作放到自己寫的獨立線程池中，例如：

/// <summary>
/// 測試GET請求
/// </summary>
/// <param name="val">測試參數</param>
[HttpGet]
[Route("TestGet")]
[SwaggerResponse(HttpStatusCode.OK, "返回JSON", typeof(JsonListResult<TestGetResult>))]
public async Task<HttpResponseMessage> TestGetAsync(string val)
{
    var task = TaskHelper.RequestTask.Run(() => //使用自己寫的獨立線程池
    {
        List<TestGetResult> list = new List<TestGetResult>();

        Thread.Sleep(5000); //模擬耗時

        for (int i = 1; i <= 10; i++)
        {
            TestGetResult item = new TestGetResult();
            item.testValue1 = i.ToString();
            item.testValue2 = i;
            item.testValue3 = "這是傳入參數：" + val;
            list.Add(item);
        }

        var jsonResult = new JsonListResult<TestGetResult>(list, list.Count);

        return ApiHelper.ToJson(jsonResult);
    });

    return await task;
}