使用CancellationToken取消特定任务
使用CancellationToken取消特定任务
提问于 2016-03-05 23:47:07
我有以下循环，它可能会动态创建一系列任务，也可能不会：
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，我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？可能有6-7个任务在任何时候运行，我需要的功能，以了解哪些正在运行，并取消一个特定的。
回答 2
Stack Overflow用户
发布于 2016-03-05 23:52:47
您可以使用DTO：class Item { Task Task; CancellationTokenSource CTS; }来跟踪每个这样的任务。保留这些项目的列表。然后，您可以随意取消它们。
Stack Overflow用户
发布于 2016-03-06 02:10:48
TL;DR;
我认为第三方物流数据流(https://msdn.microsoft.com/en-us/library/hh228603(v=vs.110).aspx在这里是一个更好的选择，但我将使用第三方物流来回答
应答
要限制并发性，您需要一个限制并发性的调度程序。我建议你在https://msdn.microsoft.com/library/system.threading.tasks.taskscheduler.aspx上搜索LimitedConcurrencyLevelTaskScheduler。
下面的代码是您试图实现的一个简单示例。
[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被尽快取消，任务1继续处理。此示例未显示，但永远不会超过7个并发任务。
不幸的是，TAP模式不能与排定程序的AttachToParent选项一起使用，或者这段代码可能会更整洁。请参阅：TaskCreationOptions.AttachedToParent is not waiting for child task
要管理CancellationTokens，您可以创建一个特定的TaskFactory，它允许如下所示：
taskFactory.StartNew(0 , () => {...});
taskFactory.Cancel(0);没有一个TaskFactory方法是虚拟的，因此您必须创建重载方法。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/35816146
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