使用取消令牌取消特定任务

本文关键字：取消 任务 令牌 | 更新日期: 2023-09-27 18:37:27

我有以下循环，它可能会也可能不会动态创建一系列任务：

While(CreateNewTask == true)
{
 if(isWorkerFree() && isValidJob() && isExecutable())
 {
   CancellationTokenSource cs = new  CancellationTokenSource();
   var myTask = Task.Run(() => Execute(cs.token);
 }
}

现在，由于这些任务是动态创建的，因此如何跟踪它们并取消特定任务或向特定任务发送取消令牌？任何时候都可能有 6-7 个任务在运行，我需要功能来知道哪些任务正在运行并取消特定的任务。

使用取消令牌取消特定任务

您可以使用 DTO： class Item { Task Task; CancellationTokenSource CTS; } 跟踪每个此类任务。保留这些项目的列表。然后，您可以随意取消它们。

TL;DR;
我认为TPL数据流（https://msdn.microsoft.com/en-us/library/hh228603（v=vs.110）.aspx）在这里是一个更好的选择，但我将使用TPL回答

答
要限制并发性，您需要一个限制并发性的调度程序。我建议你查看 https://msdn.microsoft.com/library/system.threading.tasks.taskscheduler.aspx 并搜索LimitedConcurrencyLevelTaskScheduler。

下面的代码是您要实现的目标的简单示例。

[TestClass]
public class UnitTest1
{
    [TestMethod]
    public async Task TestMethod1()
    {
        var factoryCancellation = new CancellationTokenSource();
        var scheduler = new LimitedConcurrencyLevelTaskScheduler(maxDegreeOfParallelism: 7);
        var taskFactory = new TaskFactory(factoryCancellation.Token, TaskCreationOptions.None, TaskContinuationOptions.None, scheduler);
        var taskCancellation1 = new CancellationTokenSource();
        var taskCancellation2 = new CancellationTokenSource();
        var token1 = taskCancellation1.Token;
        var token2 = taskCancellation2.Token;
        var myTask1 = taskFactory.StartNew(async () => await Execute(0, token1), token1).Unwrap();
        var myTask2 = taskFactory.StartNew(async () => await Execute(1, token2), token2).Unwrap();
        taskCancellation1.CancelAfter(500);
        try
        {
            await Task.WhenAll(myTask1, myTask2);
        }
        catch
        {
            //ThrowIfCancellationRequested Exception
        }
    }
    private async Task Execute(int i, CancellationToken token)
    {
        Console.WriteLine($"Running Task {i} : Before Delay 1");
        await Task.Delay(1000);
        token.ThrowIfCancellationRequested();
        Console.WriteLine($"Running Task {i} : Before Delay 2");
        await Task.Delay(1000);
        token.ThrowIfCancellationRequested();
        Console.WriteLine($"Running Task {i} : Before Delay 3");
        await Task.Delay(1000);
        token.ThrowIfCancellationRequested();
    }
}

这将生成以下日志

QueueTask 1  WaitingToRun
QueueTask 2  WaitingToRun
TryExecuteTask Start 1  WaitingToRun CreationOptions None
TryExecuteTask Start 2  WaitingToRun CreationOptions None
Running Task 1 : Before Delay 1
Running Task 0 : Before Delay 1
TryExecuteTask End 2 RanToCompletion IsCanceled False IsCompleted True IsFaulted False
TryExecuteTask End 1 RanToCompletion IsCanceled False IsCompleted True IsFaulted False
TryExecuteTaskInline Start 5 taskWasPreviouslyQueued False
TryExecuteTaskInline End 5 WaitingToRun IsCanceled False IsCompleted False IsFaulted False
QueueTask 5 System.Action WaitingToRun
TryExecuteTask Start 5 System.Action WaitingToRun CreationOptions None
Running Task 1 : Before Delay 2
TryExecuteTask End 5 RanToCompletion IsCanceled False IsCompleted True IsFaulted False
TryExecuteTaskInline Start 6 taskWasPreviouslyQueued False
TryExecuteTaskInline End 6 WaitingToRun IsCanceled False IsCompleted False IsFaulted False
QueueTask 6 System.Action WaitingToRun
TryExecuteTask Start 6 System.Action WaitingToRun CreationOptions None
TryExecuteTaskInline Start 8 taskWasPreviouslyQueued False
TryExecuteTaskInline End 8 RanToCompletion IsCanceled False IsCompleted True IsFaulted False
TryExecuteTask End 6 RanToCompletion IsCanceled False IsCompleted True IsFaulted False
TryExecuteTaskInline Start 12 taskWasPreviouslyQueued False
TryExecuteTaskInline End 12 WaitingToRun IsCanceled False IsCompleted False IsFaulted False
QueueTask 12 System.Action WaitingToRun
TryExecuteTask Start 12 System.Action WaitingToRun CreationOptions None
Running Task 1 : Before Delay 3
TryExecuteTask End 12 RanToCompletion IsCanceled False IsCompleted True IsFaulted False
TryExecuteTaskInline Start 14 taskWasPreviouslyQueued False
TryExecuteTaskInline End 14 WaitingToRun IsCanceled False IsCompleted False IsFaulted False
QueueTask 14 System.Action WaitingToRun
TryExecuteTask Start 14 System.Action WaitingToRun CreationOptions None
TryExecuteTaskInline Start 16 taskWasPreviouslyQueued False
TryExecuteTaskInline End 16 RanToCompletion IsCanceled False IsCompleted True IsFaulted False
TryExecuteTask End 14 RanToCompletion IsCanceled False IsCompleted True IsFaulted False

您可以看到任务 0 已尽快取消，任务 1 继续处理。此示例不显示，但永远不会超过 7 个并发任务。

不幸的是，TAP模式不适用于调度程序的AttachToParent选项，或者此代码可能更干净。请参阅：任务创建选项。附加到父任务未等待子任务

要管理CancelTokens，您可以创建一个特定的任务工厂，该任务工厂允许如下操作：

taskFactory.StartNew(0 , () => {...});
taskFactory.Cancel(0);

没有一个任务工厂方法都是虚拟的，因此您必须创建重载方法。

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