[英]how to wait for all background threads to finish (in C#)?
如何讓前台線程等待所有后台(子)線程在C#中完成? 我需要從隊列(數據庫)獲取待處理作業的列表,啟動一個新線程來執行每個作業,最后等待所有子線程完成。 如何在C#中做到這一點? 提前致謝。
您可以將每個啟動的線程存儲在一個數組中。 然后,當您需要等待它們時,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
這是不完整的代碼,但ManualResetEvent
適合您
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());
使用動態數據,您可以傳遞您的對象和WaitHandle(ActionResetEvent),它允許您等待所有后台線程完成而不聲明額外的類:
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();
}
創建一個結構來跟蹤您的工作線程
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已完成的線程數
private int _TotalThreads = 0;
private int _ThreadsHandled = 0;
private List<WorkerThreadElement> _WorkerThreadElements = new List<WorkerThreadElement>();
然后創建一個autoreset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);
您還需要一個委托來創建新線程 - 有多種方法可以做到這一點,但為了這個例子,我選擇了一個簡單的委托
// Delegate to asynchronously invoke an action
private delegate void AsyncActionExecution();
讓我們假設Invoke方法是創建所有線程並等待它們執行的入口點。 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是用於為一個操作創建單個線程的方法。 這里我們需要創建一個工作線程元素並調用實際的線程。
private void InvokeOneThread()
{
WorkerThreadElement threadElement = new WorkerThreadElement();
threadElement.WorkerThread = new AsyncActionExecution();
threadElement.WorkerThreadResult = threadElement.WorkerThread.BeginInvoke(actionParameters, InvokationCompleted, null);
_WorkerThreadElements.Add(threadElement);
}
從線程完成回調
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
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