我有一个像这样的班级工人：
public class Worker
{
private List<SomeObject> _someObjectList = null;
public Worker(SomeObject someObjectList)
{
_someObjectList = someObjectList;
}
public void Run(CancellationToken cancellationToken)
{
// Some time-consuming operation here
foreach(var elem in _someObjectList)
{
cancellationToken.ThrowIfCancellationRequested();
elem.DoSomethingLong();
}
}
}
我在工作中使用的一个表单：
public partial class SomeForm : Form
{
private Worker _worker = null;
public SomeForm(Worker worker)
{
InitializeComponent();
_worker = worker;
}
async void RunButtonClick(object sender, EventArgs e)
{
// I have a way to cancel worker from MyForm but
// I would like to be able to cancel it directly from Worker
// so object would be intuitive.
var tokenSource = new CancellationTokenSource();
var task = Task.Factory.StartNew(() => _worker.Run(tokenSource.Token), tokenSource.Token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
await task;
}
}
我需要一个更明确的解决方案来取消工人。像这样：
_worker.Cancel();
我还想像这样暂停和恢复工作人员：
_worker.Pause();
_worker.Resume();
因为我在Worker类之外实例化CancellationTokenSource，所以我看不到实现自己的Cancel方法。我已经用这样的CancellationToken实现了Pause和Resume（我觉得这是一个非常糟糕的想法，但它确实有效）：
public class Worker
{
private List<SomeObject> _someObjectList = null;
private CancellationTokenSource _pauseToken = null;
public bool Paused { get; private set; }
public Worker(SomeObject someObjectList)
{
_someObjectList = someObjectList;
}
public void Run(CancellationToken cancellationToken)
{
// Some time-consuming operation here
foreach(var elem in _someObjectList)
{
if(Paused)
_pauseToken.Token.WaitHandle.WaitOne(Timeout.Infinite);
cancellationToken.ThrowIfCancellationRequested();
elem.DoSomethingLong();
}
}
public void Pause()
{
if(!Paused)
{
// For pausing and resuming...
_pauseToken = new CancellationTokenSource();
Paused = true;
}
}
public void Resume()
{
if(Paused && _pauseToken != null)
{
_pauseToken.Cancel();
Paused = false;
}
}
}
我需要有关如何以最合适的方式实现Cancel方法和Resume / Pause方法的建议。
答案 0 :(得分：1)
如果要将取消行为封装在Worker类中，显然必须在适当的时间在适当的对象上调用CancellationTokenSource.Cancel()。有两种明显的方法可以实现这一点：
CancellationTokenSource对象嵌入Worker类本身。Worker.Cancel()方法时，它会将实际操作委托给其他类。第二种方法对我来说似乎是任意的错综复杂，而第一种方法似乎很适合你希望自己暴露Cancel()方法的类。
至于暂停和恢复，我同意你的问题下面的评论，建议使用CancellationTokenSource是为此目的滥用该类型。也就是说，在现代C＃代码中，没有理由使用ManualResetEvent之类的内容以及随之而来的伴随内容代码。
相反，您可以将Run()方法实施为async，并在await可用时将其TaskCompletionSource。然后它将有公共方法Pause()和Resume()，其中Pause()方法将创建TaskCompletionSource对象，而Resume()方法将设置结果对象
这样做，您可以正常实现Run()方法，无需额外的工作来编写管家代码以允许方法暂停和恢复。编译器将为您生成所有代码，使用await语句作为方法在暂停时可以返回的位置，然后再继续执行。
替代方法是自己编写所有管家代码（容易出错），或者甚至不从Run()方法返回，而是直接阻塞线程直到操作恢复（这是不必要的当你等待用户释放它时绑定一个帖子。）
如果您只有一个任务和一个非常简单的用户场景，这可能有点过分。阻止线程可能就足够了。但是如果你有更复杂的场景，这种方法将完全支持这些方法，同时仍然提供最有效的线程池使用。
这是一个简短的代码示例，演示了我上面描述的技术：
<强> Worker.cs
class Worker
{
private static readonly TimeSpan _ktotalDuration = TimeSpan.FromSeconds(5);
private const int _kintervalCount = 20;
public bool IsPaused { get { return _pauseCompletionSource != null; } }
public event EventHandler IsPausedChanged;
private readonly object _lock = new object();
private CancellationTokenSource _cancelSource;
private volatile TaskCompletionSource<object> _pauseCompletionSource;
public async Task Run(IProgress<int> progress)
{
_cancelSource = new CancellationTokenSource();
TimeSpan sleepDuration = TimeSpan.FromTicks(_ktotalDuration.Ticks / _kintervalCount);
for (int i = 0; i < 100; i += (100 / _kintervalCount))
{
progress.Report(i);
Thread.Sleep(sleepDuration);
_cancelSource.Token.ThrowIfCancellationRequested();
TaskCompletionSource<object> pauseCompletionSource;
lock (_lock)
{
pauseCompletionSource = _pauseCompletionSource;
}
if (pauseCompletionSource != null)
{
RaiseEvent(IsPausedChanged);
try
{
await pauseCompletionSource.Task;
}
finally
{
lock (_lock)
{
_pauseCompletionSource = null;
}
RaiseEvent(IsPausedChanged);
}
}
}
progress.Report(100);
lock (_lock)
{
_cancelSource.Dispose();
_cancelSource = null;
// Just in case pausing lost the race with cancelling or finishing
_pauseCompletionSource = null;
}
}
public void Cancel()
{
lock (_lock)
{
if (_cancelSource != null)
{
if (_pauseCompletionSource == null)
{
_cancelSource.Cancel();
}
else
{
_pauseCompletionSource.SetCanceled();
}
}
}
}
public void Pause()
{
lock (_lock)
{
if (_pauseCompletionSource == null)
{
_pauseCompletionSource = new TaskCompletionSource<object>();
}
}
}
public void Resume()
{
lock (_lock)
{
if (_pauseCompletionSource != null)
{
_pauseCompletionSource.SetResult(null);
}
}
}
private void RaiseEvent(EventHandler handler)
{
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
<强> Form1.cs的
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private Worker _worker;
private async void button1_Click(object sender, EventArgs e)
{
Progress<int> progress = new Progress<int>(i => progressBar1.Value = i);
_worker = new Worker();
_worker.IsPausedChanged += (sender1, e1) =>
{
Invoke((Action)(() =>
{
button3.Enabled = !_worker.IsPaused;
button4.Enabled = _worker.IsPaused;
}));
};
button1.Enabled = false;
button2.Enabled = button3.Enabled = true;
try
{
await Task.Run(() => _worker.Run(progress));
// let the progress bar catch up before we clear it
await Task.Delay(1000);
}
catch (OperationCanceledException)
{
MessageBox.Show("Operation was cancelled");
}
progressBar1.Value = 0;
button2.Enabled = button3.Enabled = button4.Enabled = false;
button1.Enabled = true;
}
private void button2_Click(object sender, EventArgs e)
{
_worker.Cancel();
}
private void button3_Click(object sender, EventArgs e)
{
_worker.Pause();
}
private void button4_Click(object sender, EventArgs e)
{
_worker.Resume();
}
}
<强> Form1.Designer.cs
partial class Form1
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.progressBar1 = new System.Windows.Forms.ProgressBar();
this.button1 = new System.Windows.Forms.Button();
this.button2 = new System.Windows.Forms.Button();
this.button3 = new System.Windows.Forms.Button();
this.button4 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// progressBar1
//
this.progressBar1.Anchor = ((System.Windows.Forms.AnchorStyles)(((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left)
| System.Windows.Forms.AnchorStyles.Right)));
this.progressBar1.Location = new System.Drawing.Point(12, 42);
this.progressBar1.Name = "progressBar1";
this.progressBar1.Size = new System.Drawing.Size(427, 23);
this.progressBar1.TabIndex = 0;
//
// button1
//
this.button1.Location = new System.Drawing.Point(13, 13);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(75, 23);
this.button1.TabIndex = 1;
this.button1.Text = "Start";
this.button1.UseVisualStyleBackColor = true;
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// button2
//
this.button2.Enabled = false;
this.button2.Location = new System.Drawing.Point(94, 13);
this.button2.Name = "button2";
this.button2.Size = new System.Drawing.Size(75, 23);
this.button2.TabIndex = 2;
this.button2.Text = "Cancel";
this.button2.UseVisualStyleBackColor = true;
this.button2.Click += new System.EventHandler(this.button2_Click);
//
// button3
//
this.button3.Enabled = false;
this.button3.Location = new System.Drawing.Point(175, 13);
this.button3.Name = "button3";
this.button3.Size = new System.Drawing.Size(75, 23);
this.button3.TabIndex = 3;
this.button3.Text = "Pause";
this.button3.UseVisualStyleBackColor = true;
this.button3.Click += new System.EventHandler(this.button3_Click);
//
// button4
//
this.button4.Enabled = false;
this.button4.Location = new System.Drawing.Point(256, 13);
this.button4.Name = "button4";
this.button4.Size = new System.Drawing.Size(75, 23);
this.button4.TabIndex = 4;
this.button4.Text = "Resume";
this.button4.UseVisualStyleBackColor = true;
this.button4.Click += new System.EventHandler(this.button4_Click);
//
// Form1
//
this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(451, 287);
this.Controls.Add(this.button4);
this.Controls.Add(this.button3);
this.Controls.Add(this.button2);
this.Controls.Add(this.button1);
this.Controls.Add(this.progressBar1);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);
}
#endregion
private System.Windows.Forms.ProgressBar progressBar1;
private System.Windows.Forms.Button button1;
private System.Windows.Forms.Button button2;
private System.Windows.Forms.Button button3;
private System.Windows.Forms.Button button4;
}