NotSupportedException on WaitHandle.WaitAll

Question

我正在尝试执行以下代码。代码试图以并行方式下载和保存图像。我传递要下载的图像列表。我用C# 3.0编写了这篇文章，并使用.NET Framework4 (VS.NET速成版)编译了它。每次尝试运行程序时，WaitAll操作都会导致NotSupportedException (不支持STA线程上的多个句柄的WaitAlll)。我试着删除SetMaxThreads，但这并没有什么区别。

public static void SpawnThreads(List<string> imageList){
    imageList = new List<string>(imageList);
    ManualResetEvent[] doneEvents = new ManualResetEvent[imageList.Count];
    PicDownloader[] picDownloaders = new PicDownloader[imageList.Count];
    ThreadPool.SetMaxThreads(MaxThreadCount, MaxThreadCount);
    for (int i = 0; i < imageList.Count; i++) {
        doneEvents[i] = new ManualResetEvent(false);
        PicDownloader p = new PicDownloader(imageList[i], doneEvents[i]);
        picDownloaders[i] = p;
        ThreadPool.QueueUserWorkItem(p.DoAction);
    }
    // The following line is resulting in "NotSupportedException"     
    WaitHandle.WaitAll(doneEvents);
    Console.WriteLine("All pics downloaded");
}

你能让我明白我遇到了什么问题吗？

谢谢

Answer 1

您用[STAThread]属性标记了其中一个方法吗？

Answer 2

我建议不要使用多个WaitHandle实例等待完成。使用CountdownEvent类代替。它带来了更优雅和更可伸缩的代码。此外，WaitHandle.WaitAll方法最多只支持64个句柄，不能在STA线程上调用。通过重构您的代码以使用规范模式，我想出了以下内容。

public static void SpawnThreads(List<string> imageList)
{ 
  imageList = new List<string>(imageList); 
  var finished = new CountdownEvent(1);
  var picDownloaders = new PicDownloader[imageList.Count]; 
  ThreadPool.SetMaxThreads(MaxThreadCount, MaxThreadCount); 
  for (int i = 0; i < imageList.Count; i++) 
  { 
    finished.AddCount();    
    PicDownloader p = new PicDownloader(imageList[i]); 
    picDownloaders[i] = p; 
    ThreadPool.QueueUserWorkItem(
      (state) =>
      {
        try
        {
          p.DoAction
        }
        finally
        {
          finished.Signal();
        }
      });
  } 
  finished.Signal();
  finished.Wait();
  Console.WriteLine("All pics downloaded"); 
} 

Answer 3

你试过为线程设置公寓状态吗？

thread.SetApartmentState (System.Threading.Apartmentstate.MTA );