Question

我正在尝试在多线程环境中更新进度条。我知道很多问题已经解决了这个问题，但提议的解决方案都没有对我有用。这是我的代码的主干：

public static void DO_Computation(//parameters) {
  //Intialisation of parameters

  Parallel.For(struct initialisation with local data) {
    //business logic
    //Call to update_progressbar (located in an another class, as the DO_Computation function is in Computation.cs class (not deriving from Form). 
    WinForm.Invoke((Action)delegate {Update_Progress_Bar(i);}); //WinForm is a class that exposes the  progressbar.
  }
}

这不起作用（进度条在达到100％时冻结，这是正常的（我们可以在这个问题上参考microsoft article（实际上，这不是一种线程安全的操作方法））。 Microsoft网站用于将Parallel.For循环包装到Task例程中，如下所示：

public static void DO_Computation(//parameters) {
  //Intialisation of parameters
  Task.Factory.StartNew(() =>
  {
    Parallel.For(struct initialosation with local data) {
      //business logic
      //Call to update_progressbar (ocated in an another class, as the DO_Computation function is in Computation.cs class (not deriving from Form). 
      WinForm.Invoke((Action)delegate {Update_Progress_Bar(i);}); //WinForm is a class that exposes the  progressbar.
      ..
    }
  });
});

然而，当调试线程直接退出Task范围时，这也不起作用。

编辑2：

基本上，我的问题分为3部分：Computation.cs（公开DO_Computation），WinForm这是包含进度条的表单，MainWindow是包含按钮的表单，单击该按钮会打开带有进度条的表单。

我不清楚什么是＆＃34;任务＆＃34;在这种情况下。因为它没有执行任何Parallel.For工作

而超出任务范围

有什么想法吗？

非常感谢，

编辑3：

我在Noseratio的帮助下升级了我的代码（对他来说很多）。但是我遇到了同样的问题，即任务中的代码永远不会被执行。我的代码现在看起来像：



DoComputation method
   //Some Initilasations here 
    Action enableUI = () =>
    {
    frmWinProg.SetProgressText("Grading Transaction...");
    frmWinProg.ChangeVisibleIteration(true);
    };
    Action<Exception> handleError = (ex) =>
    {
    // error reporting
    MessageBox.Show(ex.Message);
    };
    var cts = new CancellationTokenSource();
    var token = cts.Token;
    Action cancel_work = () =>
    {
    frmWinProg.CancelTransaction();
    cts.Cancel();
    };
    var syncConext = SynchronizationContext.Current;
    Action<int> progressReport = (i) =>
    syncConext.Post(_ => frmWinProg.SetIteration(i,GrpModel2F.NumOfSim, true), null);
    var task = Task.Factory.StartNew(() =>
    {
    ParallelLoopResult res = Parallel.For<LocalDataStruct>(1,NbSim, options,
    () => new DataStruct(//Hold LocalData for each thread),
    (iSim, loopState, DataStruct) => 
    //Business Logic 
    if (token.IsCancellationRequested)
    {
    loopState.Stop();
    }
    progressReport(iSim);
    //Business Logic
    return DataStruct;
    },
    (DataStruct) => 
    //Assiginig Results;
    });//Parallel.For end
    }, token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
    task.ContinueWith(_ =>
    {
    try
    {
    task.Wait();
    }
    catch (Exception ex)
    {
    while (ex is AggregateException && ex.InnerException != null)
    ex = ex.InnerException;
    handleError(ex);
    }
    enableUI();
    }, TaskScheduler.FromCurrentSynchronizationContext

（））;

请注意，Do_Computation函数本身是从运行BackGroundWorker的Form调用的。

Answer 1

使用async/await，Progress<T>并使用CancellationTokenSource观看取消。

好的阅读，相关："Async in 4.5: Enabling Progress and Cancellation in Async APIs"。

如果您需要定位.NET 4.0但使用VS2012 +进行开发，您仍然可以使用async/await，Microsoft会为此提供Microsoft.Bcl.Async库。

我已经整理了一个WinForms示例，说明了上述所有内容。它还显示了如何使用Parallel.For：

观察ParallelLoopState.Stop()循环的取消

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication_22487698
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();
        }

        IEnumerable<int> _data = Enumerable.Range(1, 100);
        Action _cancelWork;

        private void DoWorkItem(
            int[] data,
            int item,
            CancellationToken token,
            IProgress<int> progressReport,
            ParallelLoopState loopState)
        {
            // observe cancellation
            if (token.IsCancellationRequested)
            {
                loopState.Stop();
                return;
            }

            // simulate a work item
            Thread.Sleep(500);

            // update progress
            progressReport.Report(item);
        }

        private async void startButton_Click(object sender, EventArgs e)
        {
            // update the UI
            this.startButton.Enabled = false;
            this.stopButton.Enabled = true;

            try
            {
                // prepare to handle cancellation
                var cts = new CancellationTokenSource();
                var token = cts.Token;

                this._cancelWork = () =>
                {
                    this.stopButton.Enabled = false;
                    cts.Cancel();
                };

                var data = _data.ToArray();
                var total = data.Length;

                // prepare the progress updates
                this.progressBar.Value = 0;
                this.progressBar.Minimum = 0;
                this.progressBar.Maximum = total;

                var progressReport = new Progress<int>((i) =>
                {
                    this.progressBar.Increment(1);
                });

                // offload Parallel.For from the UI thread 
                // as a long-running operation
                await Task.Factory.StartNew(() =>
                {
                    Parallel.For(0, total, (item, loopState) =>
                        DoWorkItem(data, item, token, progressReport, loopState));
                    // observe cancellation
                    token.ThrowIfCancellationRequested();
                }, token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            // update the UI
            this.startButton.Enabled = true;
            this.stopButton.Enabled = false;
            this._cancelWork = null;
        }

        private void stopButton_Click(object sender, EventArgs e)
        {
            if (this._cancelWork != null)
                this._cancelWork();
        }
    }
}

已更新，以下是在没有async/await的情况下执行相同操作的方法：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication_22487698
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();
        }

        IEnumerable<int> _data = Enumerable.Range(1, 100);
        Action _cancelWork;

        private void DoWorkItem(
            int[] data,
            int item,
            CancellationToken token,
            Action<int> progressReport,
            ParallelLoopState loopState)
        {
            // observe cancellation
            if (token.IsCancellationRequested)
            {
                loopState.Stop();
                return;
            }

            // simulate a work item
            Thread.Sleep(500);

            // update progress
            progressReport(item);
        }

        private void startButton_Click(object sender, EventArgs e)
        {
            // update the UI
            this.startButton.Enabled = false;
            this.stopButton.Enabled = true;

            Action enableUI = () =>
            {
                // update the UI
                this.startButton.Enabled = true;
                this.stopButton.Enabled = false;
                this._cancelWork = null;
            };

            Action<Exception> handleError = (ex) =>
            {
                // error reporting
                MessageBox.Show(ex.Message);
            };

            try
            {
                // prepare to handle cancellation
                var cts = new CancellationTokenSource();
                var token = cts.Token;

                this._cancelWork = () =>
                {
                    this.stopButton.Enabled = false;
                    cts.Cancel();
                };

                var data = _data.ToArray();
                var total = data.Length;

                // prepare the progress updates
                this.progressBar.Value = 0;
                this.progressBar.Minimum = 0;
                this.progressBar.Maximum = total;

                var syncConext = SynchronizationContext.Current;

                Action<int> progressReport = (i) =>
                    syncConext.Post(_ => this.progressBar.Increment(1), null);

                // offload Parallel.For from the UI thread 
                // as a long-running operation
                var task = Task.Factory.StartNew(() =>
                {
                    Parallel.For(0, total, (item, loopState) =>
                        DoWorkItem(data, item, token, progressReport, loopState));
                    // observe cancellation
                    token.ThrowIfCancellationRequested();
                }, token, TaskCreationOptions.LongRunning, TaskScheduler.Default);

                task.ContinueWith(_ => 
                {
                    try
                    {
                        task.Wait(); // rethrow any error
                    }
                    catch (Exception ex)
                    {
                        while (ex is AggregateException && ex.InnerException != null)
                            ex = ex.InnerException;
                        handleError(ex);
                    }
                    enableUI();
                }, TaskScheduler.FromCurrentSynchronizationContext());
            }
            catch (Exception ex)
            {
                handleError(ex);
                enableUI();
            }
        }

        private void stopButton_Click(object sender, EventArgs e)
        {
            if (this._cancelWork != null)
                this._cancelWork();
        }
    }
}

并行循环调用中的进度条

1 个答案: