并行循环调用中的进度条
本文关键字：循环 调用 并行 | 更新日期: 2023-09-27 17:50:46
我正在尝试在多线程环境中更新进度条。我知道有很多问题已经涉及到这个问题，但没有一个建议的解决方案对我有效。下面是我的代码的主干:
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(进度条在到达100%时冻结，这是正常的(我们可以参考微软关于这个问题的文章(实际上，这不是一个线程安全的操作方法))。Microsoft站点规定将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.
..
}
});
});
但是，当调试线程直接退出Task作用域时，这就不能正常工作了。
编辑2:
基本上，我的问题分为3部分:Computation.cs(其中DO_Computation暴露)，WinForm这是包含进度条的表单，和MainWindow这是包含按钮的表单，当点击打开与进度条的表单。
我不清楚"Task"在这种情况下有什么用。因为它在没有执行任何Parallel.For工作的情况下离开了Task范围
任何想法?
Many Thanks，
编辑3:
我在Noseratio的帮助下升级了我的代码(感谢他)。然而，我有同样的问题，这是代码内的任务是永远不会执行。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之前());
注意，Do_Computation函数本身是从一个运行BackGroundWorker的Form中调用的。
使用async/await, Progress<T>并观察与CancellationTokenSource相消
值得一读，相关:"Async in 4.5:在Async api中启用进度和取消"。
如果你需要以。net 4.0为目标，但使用VS2012+开发，你仍然可以使用async/await，微软为此提供了Microsoft.Bcl.Async库。
我把一个WinForms的例子放在一起来说明上面的所有内容。它还展示了如何使用ParallelLoopState.Stop():
Parallel.For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();
}
}
}
更新了，这里是如何在没有async/await的情况下做同样的事情:
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();
}
}
}