沒有UI線程的任務同步

Question

在下面的代碼中，我想同步任務列表的結果報告。這是因爲task.Result阻塞，直到任務完成。但是，任務ID = 3需要很長時間才能完成，並阻止所有其他已完成的任務報告其狀態。

我認爲我可以通過將報告（Console.Write）移動到.ContinueWith指令中，但我沒有UI線程，因此如何獲取TaskScheduler來同步.ContinueWith任務？

我現在擁有的一切：

static void Main(string[] args) 
{ 
    Console.WriteLine("Starting on {0}", Thread.CurrentThread.ManagedThreadId); 

    var tasks = new List<Task<int>>(); 

    for (var i = 0; i < 10; i++) 
    { 
     var num = i; 
     var t = Task<int>.Factory.StartNew(() => 
     { 
      if (num == 3) 
      { 
       Thread.Sleep(20000); 
      } 
      Thread.Sleep(new Random(num).Next(1000, 5000)); 
      Console.WriteLine("Done {0} on {1}", num, Thread.CurrentThread.ManagedThreadId); 
      return num; 
     }); 
     tasks.Add(t); 
    } 

    foreach (var task in tasks) 
    { 
     Console.WriteLine("Completed {0} on {1}", task.Result, Thread.CurrentThread.ManagedThreadId); 
    } 

    Console.WriteLine("End of Main"); 
    Console.ReadKey(); 
} 

我想移動到這個或類似的東西，但我需要的Console.Write（「已完成...」），以一切發生在同一線程上：

static void Main(string[] args) 
{ 
    Console.WriteLine("Starting on {0}", Thread.CurrentThread.ManagedThreadId); 

    for (var i = 0; i < 10; i++) 
    { 
     var num = i; 
     Task<int>.Factory.StartNew(() => 
     { 
      if (num == 3) 
      { 
       Thread.Sleep(20000); 
      } 
      Thread.Sleep(new Random(num).Next(1000, 10000)); 
      Console.WriteLine("Done {0} on {1}", num, Thread.CurrentThread.ManagedThreadId); 
      return num; 
     }).ContinueWith(value => 
     { 
      Console.WriteLine("Completed {0} on {1}", value.Result, Thread.CurrentThread.ManagedThreadId); 
     } 

    /* need syncronization context */); 
    } 

    Console.WriteLine("End of Main"); 
    Console.ReadKey(); 
} 

- 解決方案 - 得到一些意見和閱讀部分的解決方案，這是完整的解決方案，我想要做什麼之後。這裏的目標是儘可能快地處理長時間運行的任務，然後對每個任務的結果進行一次處理。

static void Main(string[] args) 
{ 
    Console.WriteLine("Starting on {0}", Thread.CurrentThread.ManagedThreadId); 

    var results = new BlockingCollection<int>(); 

    Task.Factory.StartNew(() => 
    { 
     while (!results.IsCompleted) 
     { 
      try 
      { 
       var x = results.Take(); 
       Console.WriteLine("Completed {0} on {1}", x, Thread.CurrentThread.ManagedThreadId); 
      } 
      catch (InvalidOperationException) 
      { 
      } 
     } 
     Console.WriteLine("\r\nNo more items to take."); 
    }); 

    var tasks = new List<Task>(); 

    for (var i = 0; i < 10; i++) 
    { 
     var num = i; 
     var t = Task.Factory.StartNew(() => 
     { 
      if (num == 3) 
      { 
       Thread.Sleep(20000); 
      } 
      Thread.Sleep(new Random(num).Next(1000, 10000)); 
      Console.WriteLine("Done {0} on {1}", num, Thread.CurrentThread.ManagedThreadId); 
      results.Add(num); 
     }); 

     tasks.Add(t); 
    } 

    Task.Factory.ContinueWhenAll(tasks.ToArray(), _ => results.CompleteAdding()); 

    Console.WriteLine("End of Main"); 
    Console.ReadKey(); 
} 

Answer 1

你必須建立某種形式的作家的任務，但是，請記住，即使此任務可以被重新安排到其他本地或託管線程！使用TPL中的默認調度程序，您無法控制哪個託管線程接收工作。

public class ConcurrentConsole 
{ 
    private static BlockingCollection<string> output 
     = new BlockingCollection<string>(); 

    public static Task CreateWriterTask(CancellationToken token) 
    { 
     return new Task(
      () => 
      { 
       while (!token.IsCancellationRequested) 
       { 
        string nextLine = output.Take(token); 
        Console.WriteLine(nextLine); 
       } 
      }, 
      token); 
    } 

    public static void WriteLine(Func<string> writeLine) 
    { 
     output.Add(writeLine()); 
    } 
} 

當我打開你的代碼中使用這個我收到了以下的輸出：

End of Main 
Done 1 on 6 
Completed 1 on 6 
Done 5 on 9 
Completed 5 on 9 
Done 0 on 4 
Completed 0 on 4 
Done 2 on 5 
Completed 2 on 13 
Done 7 on 10 
Completed 7 on 10 
Done 4 on 8 
Completed 4 on 5 
Done 9 on 12 
Completed 9 on 9 
Done 6 on 6 
Completed 6 on 5 
Done 8 on 11 
Completed 8 on 4 
Done 3 on 7 
Completed 3 on 7 

即使你的代碼發送() => String.Format("Completed {0} on {1}"...到ConcurrentConsole.WriteLine，確保ManagedThreadId將是對ConcurrentConsole任務回升，它仍然會改變它運行的線程。儘管比正在執行的任務更少變化。

Answer 2

我建議：

1）創建的鎖定對象
2）創建一個字符串列表寫入
3）因爲它產生的循環，睡了一下線程，然後鎖定字符串列表，然後如果它不是空的，寫入所有這些並清空列表
4）其他線程然後鎖定列表，添加它們的狀態，解鎖並繼續。

object writeListLocker = new object(); 
List<string> linesToWrite = new List<string>(); 

// Main thread loop 
for (; ;) 
{ 
    lock (writerListLocker) 
    { 
     foreach (string nextLine in linesToWrite) 
      Console.WriteLine(nextLine); 
     linesToWrite.Clear(); 
    } 
    Thread.Sleep(500); 
} 

// Reporting threads 
lock (writerListLocker) 
{ 
    linesToWrite.Add("Completed (etc.)"); 
} 

Answer 3

您可以使用OrderedTaskScheduler確保一次只運行一個任務;但是，它們將在線程池線程上運行（不一定全部在同一個線程上）。

如果你真的需要在同一個線程上（而不是一次一個），那麼你可以使用ActionThread從Nito.Async library。它爲其代碼提供SynchronizationContext，可以通過FromCurrentSynchronizationContext找到。

Answer 4

我想你會期待像下面這樣的結果。

Starting on 8 
Done 1 on 11 
Completed 1 on 9 
Done 5 on 11 
Completed 5 on 9 
Done 0 on 10 
Completed 0 on 9 
Done 2 on 12 
Completed 2 on 9 
Done 7 on 16 
Completed 7 on 9 
Done 4 on 14 
Completed 4 on 9 
Done 9 on 18 
Completed 9 on 9 
Done 6 on 15 
Completed 6 on 9 
Done 8 on 17 
Completed 8 on 9 
Done 3 on 13 
Completed 3 on 9 

如下，我用StaSynchronizationContext在我的代碼從the Understanding SynchronizationContext其中一個線程同步調用很好地解釋。請參考它。

我的代碼片斷是：

static void Main(string[] args) 
{ 
    StaSynchronizationContext context = new StaSynchronizationContext(); 
    StaSynchronizationContext.SetSynchronizationContext(context); 
    Console.WriteLine("Starting on {0}", Thread.CurrentThread.ManagedThreadId); 
    for (var i = 0; i < 10; i++) 
    { 
     var num = i; 
     Task<int>.Factory.StartNew(() => 
     { 
      if (num == 3) 
      { 
       Thread.Sleep(20000); 
      } 
      Thread.Sleep(new Random(num).Next(1000, 10000)); 
      Console.WriteLine("Done {0} on {1}", num, Thread.CurrentThread.ManagedThreadId); 
      return num; 
     }).ContinueWith(
     value => 
     { 
      Console.WriteLine("Completed {0} on {1}", value.Result, Thread.CurrentThread.ManagedThreadId); 
     } 
     ,TaskScheduler.FromCurrentSynchronizationContext()); 
    } 
    Console.WriteLine("End of Main"); 
    Console.ReadKey(); 
}