不同請求中的共享對象

Question

我正在使用.NET 3.5和一個簡單的http請求處理程序。現在，在每個http請求中，我的處理程序會打開一個與3個遠程服務器的tcp連接，以便從它們接收一些信息。然後關閉套接字並將服務器狀態寫回Context.Response。

但是，我寧願有一個單獨的對象，每隔5分鐘通過tcp連接到遠程服務器，獲取信息並保留它。所以每個請求上的HttpRequest只要求這個對象提供信息就快得多。

所以我的問題在這裏是，如何保持一個共享的全局對象在內存中所有可也「喚醒」的做那些TCP連接連時候沒有HTTP請求來了，有對象入店到HTTP請求處理程序。

Answer 1

一個服務可能是這個矯枉過正。

您可以在您的應用程序啓動中創建一個全局對象，並讓它創建一個後臺線程，每5分鐘執行一次查詢。將響應（或響應中處理的內容）放到單獨的類中，爲每個響應創建該類的新實例，並在每次檢索響應時使用System.Threading.Interlocked.Exchange來替換靜態實例。當你想要查看響應時，只需將靜態實例的引用複製到堆棧引用，並且您將擁有最新的數據。

但請記住，只要沒有一定的時間（空閒時間）請求，ASP.NET就會終止您的應用程序，因此您的應用程序將停止並重新啓動，導致您的全局對象被破壞並重建。

你可能在其他地方看過你不能或不應該在ASP.NET中做背景的東西，但事實並非如此 - 你只需要瞭解它的含義。我在處理超過1000 req/sec峯值（跨多個服務器）的ASP.NET站點上使用與以下示例類似的代碼。

例如，在的global.asax.cs：

public class BackgroundResult 
    { 
     public string Response; // for simplicity, just use a public field for this example--for a real implementation, public fields are probably bad 
    } 
    class BackgroundQuery 
    { 
     private BackgroundResult _result; // interlocked 
     private readonly Thread _thread; 

     public BackgroundQuery() 
     { 
      _thread = new Thread(new ThreadStart(BackgroundThread)); 
      _thread.IsBackground = true; // allow the application to shut down without errors even while this thread is still running 
      _thread.Name = "Background Query Thread"; 
      _thread.Start(); 

      // maybe you want to get the first result here immediately?? Otherwise, the first result may not be available for a bit 
     } 

     /// <summary> 
     /// Gets the latest result. Note that the result could change at any time, so do expect to reference this directly and get the same object back every time--for example, if you write code like: if (LatestResult.IsFoo) { LatestResult.Bar }, the object returned to check IsFoo could be different from the one used to get the Bar property. 
     /// </summary> 
     public BackgroundResult LatestResult { get { return _result; } } 

     private void BackgroundThread() 
     { 
      try 
      { 
       while (true) 
       { 
        try 
        { 
         HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("http://example.com/samplepath?query=query"); 
         request.Method = "GET"; 
         using (HttpWebResponse response = (HttpWebResponse)request.GetResponse()) 
         { 
          using (StreamReader reader = new StreamReader(response.GetResponseStream(), System.Text.Encoding.UTF8)) 
          { 
           // get what I need here (just the entire contents as a string for this example) 
           string result = reader.ReadToEnd(); 
           // put it into the results 
           BackgroundResult backgroundResult = new BackgroundResult { Response = result }; 
           System.Threading.Interlocked.Exchange(ref _result, backgroundResult); 
          } 
         } 
        } 
        catch (Exception ex) 
        { 
         // the request failed--cath here and notify us somehow, but keep looping 
         System.Diagnostics.Trace.WriteLine("Exception doing background web request:" + ex.ToString()); 
        } 
        // wait for five minutes before we query again. Note that this is five minutes between the END of one request and the start of another--if you want 5 minutes between the START of each request, this will need to change a little. 
        System.Threading.Thread.Sleep(5 * 60 * 1000); 
       } 
      } 
      catch (Exception ex) 
      { 
       // we need to get notified of this error here somehow by logging it or something... 
       System.Diagnostics.Trace.WriteLine("Error in BackgroundQuery.BackgroundThread:" + ex.ToString()); 
      } 
     } 
    } 
    private static BackgroundQuery _BackgroundQuerier; // set only during application startup 

    protected void Application_Start(object sender, EventArgs e) 
    { 
     // other initialization here... 
     _BackgroundQuerier = new BackgroundQuery(); 
     // get the value here (it may or may not be set quite yet at this point) 
     BackgroundResult result = _BackgroundQuerier.LatestResult; 
     // other initialization here... 
    }