如何等待所有後臺線程完成（在C＃中）？

Question

如何讓前臺線程等待所有後臺（子）線程在C＃中完成？我需要從隊列（數據庫）中獲取待處理作業的列表，啓動一個新線程來執行它們中的每一個，並最終等待所有子線程完成。如何在C＃中做到這一點？提前致謝。

Answer 1

考慮使用線程池。你想要的大部分已經完成了。有一個example from Microsoft它幾乎完成你的整個任務。將「fibonacci」替換爲「數據庫任務」，聽起來像是你的問題。

Answer 2

您可以將每個啓動的線程存儲在一個數組中。然後當你需要等待它們全部時，在循環中的數組中的每個線程上調用Join方法。

Thread child = new Thread(...); 
Threads.Add(child); 
child.Start() 

... 

foreach(Thread t in Threads) 
{ 
    t.Join(); 
} 

HTH

Answer 3

這是不完整的代碼，但ManualResetEvent爲你的作品

var waitEvents = new List<ManualResetEvent>(); 
foreach (var action in actions) 
{ 
    var evt = new ManualResetEvent(false); 
    waitEvents.Add(evt); 
    ThreadPool.RegisterWaitForSingleObject(asyncResult.AsyncWaitHandle, TimeoutCallback, state, 5000, true); 
} 

if (waitEvents.Count > 0) 
    WaitHandle.WaitAll(waitEvents.ToArray()); 

Answer 4

創建一個結構，讓您的工作線程的跟蹤

private struct WorkerThreadElement 
{ 
    public IAsyncResult WorkerThreadResult; 
    public AsyncActionExecution WorkerThread; 
} 

您還需要跟蹤預期要創建的線程總數以及當前有多少個線程完成

private int _TotalThreads = 0; 
private int _ThreadsHandled = 0; 
private List<WorkerThreadElement> _WorkerThreadElements = new List<WorkerThreadElement>(); 

然後創建一個自動復位句柄以等待線程完成。

// The wait handle thread construct to signal the completion of this process 
private EventWaitHandle _CompletedHandle = new AutoResetEvent(false); 

你還需要一個委託創建新主題 - 這樣做有多種方式，但我選擇了一個簡單的委託爲這個例子的目的

// Delegate to asynchronously invoke an action 
private delegate void AsyncActionExecution(); 

讓asume的Invoke方法是創建所有線程並等待其執行的入口點。所以我們有：

public void Invoke() 
{ 
    _TotalThreads = N; /* Change with the total number of threads expected */ 

    foreach (Object o in objects) 
    { 
     this.InvokeOneThread(); 
    }    

    // Wait until execution has been completed 
    _CompletedHandle.WaitOne(); 

    // Collect any exceptions thrown and bubble them up 
    foreach (WorkerThreadElement workerThreadElement in _WorkerThreadElements) 
    { 
     workerThreadElement.WorkerThread.EndInvoke(workerThreadElement.WorkerThreadResult); 
    } 
}   

InvokeOneThread是用於爲一個操作創建單個線程的方法。這裏我們需要創建一個工作線程元素並調用實際的線程。從線程完成

private void InvokeOneThread() 
{ 
    WorkerThreadElement threadElement = new WorkerThreadElement(); 
    threadElement.WorkerThread = new AsyncActionExecution(); 
    threadElement.WorkerThreadResult = threadElement.WorkerThread.BeginInvoke(actionParameters, InvokationCompleted, null); 

    _WorkerThreadElements.Add(threadElement); 
} 

回調

private object _RowLocker = new object(); 

/// <summary> 
/// Increment the number of rows that have been fully processed 
/// </summary> 
/// <param name="ar"></param> 
private void InvokationCompleted(IAsyncResult ar) 
{ 
    lock (_RowLocker) 
    { 
     _RowsHandled++; 
    } 

    if (_TotalThreads == _ThreadsHandled) 
     _CompletedHandle.Set(); 
} 

完成

Answer 5

使用動態數據，你可以通過你的對象和WaitHandle的（ActionResetEvent），讓你等待所有的後臺線程完成不宣而一個額外的類：[C＃產生多個線程的

static void Main(string[] args) 
{ 
    List<AutoResetEvent> areList = new List<AutoResetEvent>(); 
    foreach (MyObject o in ListOfMyObjects) 
    { 
     AutoResetEvent are = new AutoResetEvent(false); 
     areList.Add(are); 
     ThreadPool.QueueUserWorkItem(DoWork, new { o, are }); 
    }; 

    Console.WriteLine("Time: {0}", DateTime.Now); 
    WaitHandle.WaitAll(areList.ToArray()); 
    Console.WriteLine("Time: {0}", DateTime.Now); 
    Console.ReadKey(); 
} 

static void DoWork(object state) 
{ 
    dynamic o = state; 
    MyObject myObject = (MyObject)o.o; 
    AutoResetEvent are = (AutoResetEvent)o.are; 

    myObject.Execute(); 
    are.Set(); 
}