Parallel.Foreach + BackgroundWorker.ReportProgress

Question

如果有任何已知原因我不应该这样做，我正在寻找反馈：将 ReportProgress 放在并行 foreach 语句中。是否有任何类似的方法可以实现相同的目标，但被认为更安全或更好？

代码示例：

        int iterations = 0;
        int count = items.Count;
        Parallel.ForEach(items, new ParallelOptions() { MaxDegreeOfParallelism = 5 }, item =>
        {
            iterations++;
            int percentComplete = (iterations/count) * 100;
            backgroundWorker.ReportProgress(percentComplete);
        };

附加信息：

我有一个需要执行管理项目的特定任务的 Windows 窗体程序。使用多线程使其速度更快。但是，它需要向表单上的进度条报告已完成的整体进度，因此最终用户不会怀疑程序是否冻结。在某些情况下，整个工作可能需要几个小时。因此，必须要有进度条。

Answer 1

我认为这是不明智的，甚至可能不允许让多个线程与同一个BackGroundWorker 通信。

如果您只有有限数量的线程，例如您的示例中的 5 个，请考虑让每个线程使用自己的 BackgroundWorker 来报告自己的进度。

所有进度报告的接收者应在收到报告后确定实际进度并将其报告给感兴趣的人。

class MyLongProgress : IDisposable
{
     public MyLongProgress()
     {
         for (int i=0; i<maxNrOfParallelProcesses; ++i)
         {
             var createdBackGroundWorker = this.CreateBackGroundWorker();
             createdBackGroundWorker.ReportProgress += this.OnProgressReport;
             backGroundWorkers.Add(createdBackGroundWorker);
         }
     }
     // TODO: implement Disposable pattern that Disposes the background workers
     private readonly List<BackGroundWorker> backGroundWorkers = new List<BackGroundWorker>();

     public void StartLongProcess()
     {
         // start your long progress, which involves starting the backGroundWorkers
         // These backGroundWorkers will report progress via OnProgressReport
     }

     private void OnProgressReport(object sender, ...)
     {
         var myBackGroundWorker = (BackGroundWorker)sender;
         // calculate the actual progress using earlier received progress reports
         MyProgressReport report = ...
         OnReportProgress(report);
     }

     public event EventHandler<MyprogressReport> ReportProgrogress;

     protected virtual void OnReportProgress(MyProgressReport report)
     {
         this.ReportProgress?.Invoke(this, report);
     }
}

或者：仅在 StartLongProcess 期间创建和处置 BackGroundWorker。在这种情况下，您不需要 IDisposable。

Answer 2

我认为 Harald 的回答很成功。 在拥有一名后台工作人员的情况下，我使用了this link 中显示的示例。

您可以很好地了解它如何与以下 sn-p 一起工作（从上面的链接复制）。我认为您可以使用它作为基础来允许 DoWorkEventHandler 代表的集合并为每个代表创建一个 BackgroundWorker。

      private void button4_Click(object sender, EventArgs e)
      {
         // Create dialog.
         ProgressWithCancel dlgProgress = new ProgressWithCancel( "Testing progress", LongOperation);

         // Show dialog with Synchronous/blocking call.
         // LongOperation() is called by dialog.
         dlgProgress.ShowDialog(); // Synchronous/blocking call.
      }

      private void LongOperation(object sender, DoWorkEventArgs e)
      {
         BackgroundWorker worker = sender as BackgroundWorker;

         int max = 20;
         for (int i = 0; i < max; i++)
         {
            if (worker.CancellationPending) // See if cacel button was pressed.
            {
               System.Threading.Thread.Sleep(2000); // Similate time for clean-up.
               break;
            }

            int percent = i * 100 / max;

            string userState = percent.ToString(); // render a string to display on the progress dialog.

            // Append to string just to show multi-line user-status info.
            if (percent >= 45 && percent <= 55) { userState += "Half way"; }
            if (percent >= 85) { userState += "Almost done"; }

            worker.ReportProgress(percent, userState); // Report percent and user-status info to dialog.

            System.Threading.Thread.Sleep(800); // Simulate time-consuming operation
         }
      }


// Implementation (in ProgressWithCancel.cs)

namespace ProgressWithCancel
{
   public partial class ProgressWithCancel : Form
   {
      public ProgressWithCancel(string whyWeAreWaiting, DoWorkEventHandler work)
      {
         InitializeComponent();
         this.Text = whyWeAreWaiting; // Show in title bar
         backgroundWorker1.DoWork += work; // Event handler to be called in context of new thread.
      }

      private void btnCancel_Click(object sender, EventArgs e)
      {
         label1.Text = "Cancel pending";
         backgroundWorker1.CancelAsync(); // Tell worker to abort.
         btnCancel.Enabled = false;
      }

      private void Progress_Load(object sender, EventArgs e)
      {
         backgroundWorker1.RunWorkerAsync();
      }

      private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
      {
         progressBar1.Value = e.ProgressPercentage;
         label1.Text = e.UserState as string;
      }

      private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
      {
         Close();
      }

   }
}