什么是“cancellationToken”在TaskFactory.StartNew()中用于什么？

发布于 2024-09-19 08:01:52 字数 1787 浏览 3 评论 0原文

http://msdn.microsoft.com/en-us/library/dd988458.aspx

UPD：

那么，让我们讨论这篇文章：http://msdn.microsoft.com/en-us/library/dd997396.aspx

我稍微更改了该代码：

    static void Main()
    {

        var tokenSource2 = new CancellationTokenSource();
        CancellationToken ct = tokenSource2.Token;

        var task = Task.Factory.StartNew(() =>
        {

            // Were we already canceled?
            ct.ThrowIfCancellationRequested();

            bool moreToDo = true;
            Thread.Sleep(5000);
            while (moreToDo)
            {

                // Poll on this property if you have to do
                // other cleanup before throwing.
                if (ct.IsCancellationRequested)
                {
                    Console.WriteLine("exit");
                    // Clean up here, then...
                    ct.ThrowIfCancellationRequested();
                }

            }
        }, tokenSource2.Token); // this parameter useless

        Console.WriteLine("sleep");
        Thread.Sleep(2000);
        Console.WriteLine("cancel");

        tokenSource2.Cancel();

        // Just continue on this thread, or Wait/WaitAll with try-catch:
        try
        {
            task.Wait();
        }
        catch (AggregateException e)
        {
            foreach (var v in e.InnerExceptions)
            {
                Console.WriteLine(e.Message + " " + v.Message);
            }
        }

        Console.ReadKey();
    }

UPD：嗯，这仅更改task.IsCanceled，恕我直言，这是无用的，因为我仍然应该手动实现所有操作。

原文

http://msdn.microsoft.com/en-us/library/dd988458.aspx

UPD:

so, let's discuss this article then: http://msdn.microsoft.com/en-us/library/dd997396.aspx

I've changed that code a little:

    static void Main()
    {

        var tokenSource2 = new CancellationTokenSource();
        CancellationToken ct = tokenSource2.Token;

        var task = Task.Factory.StartNew(() =>
        {

            // Were we already canceled?
            ct.ThrowIfCancellationRequested();

            bool moreToDo = true;
            Thread.Sleep(5000);
            while (moreToDo)
            {

                // Poll on this property if you have to do
                // other cleanup before throwing.
                if (ct.IsCancellationRequested)
                {
                    Console.WriteLine("exit");
                    // Clean up here, then...
                    ct.ThrowIfCancellationRequested();
                }

            }
        }, tokenSource2.Token); // this parameter useless

        Console.WriteLine("sleep");
        Thread.Sleep(2000);
        Console.WriteLine("cancel");

        tokenSource2.Cancel();

        // Just continue on this thread, or Wait/WaitAll with try-catch:
        try
        {
            task.Wait();
        }
        catch (AggregateException e)
        {
            foreach (var v in e.InnerExceptions)
            {
                Console.WriteLine(e.Message + " " + v.Message);
            }
        }

        Console.ReadKey();
    }

UPD: Well, this changes only task.IsCanceled, which is imho useless, due to I still ought to implement all manually.

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我做我的改变 2024-09-26 08:01:52

由于评论，我发布了另一个答案。

考虑以下代码：

var tokenSource = new CancellationTokenSource();
CancellationToken ct = tokenSource.Token;

tokenSource.Cancel(); 

var task = Task.Factory.StartNew(() =>
{    
  // Were we already canceled?
  ct.ThrowIfCancellationRequested();
  // do some processing
});

即使在任务实际启动之前调用 tokenSource.Cancel() ，您仍然会从线程池中分配一个工作线程，因此您会浪费一些系统资源。

但是，当您在 Task.Factory.StartNew 中指定 token 参数时，任务将立即取消，而不分配工作线程。

Due to comments, I'm posting another answer.

Consider the following code:

var tokenSource = new CancellationTokenSource();
CancellationToken ct = tokenSource.Token;

tokenSource.Cancel(); 

var task = Task.Factory.StartNew(() =>
{    
  // Were we already canceled?
  ct.ThrowIfCancellationRequested();
  // do some processing
});

Even if the call tokenSource.Cancel() is issued before the task was actually started, you'll still allocate a worker thread from thread pool, so you'll waste some system resources.

But when you specify token argument in Task.Factory.StartNew, the task will be cancelled immediately, without allocating a worker thread.

回复收藏 0 原文

埖埖迣鎅 2024-09-26 08:01:52

取消任务仍然是合作的。您不希望线程在某些关键操作中被终止。你需要检查一下。

CancellationTokens 比诸如 ManualResetEvent 之类的更简单的结构更好，因为您可以级联或组合它们，例如，您可以将它们用于整个应用程序关闭，也可以将其与一个用于取消的组合一项特定任务。该任务只需查看一个 CancellationToken，但您可以从任一 CancellationTokenSource 取消它。