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POC# async CTP - How do I mark an async task as canceled without throwing a TaskCanceledException?
 

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  1. POC# async CTP - How do I mark an async task as canceled without throwing a TaskCanceledException?
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    <p>I have a short async task that will frequently need to be canceled after it has started. The "Task" class has an IsCanceled indicator which I think would be convenient to use to indicate that the async task was canceled without running to completion, but as far as I can tell the only way to have an async Task be marked as canceled is to throw a TaskCanceledException in the async function. Throwing an exception routinely, to indicate a situation which occurs unexceptionally, goes against how I understand exceptions should be used. Does anyone know a better way to indicate an async task to be canceled when it is expected to happen frequently? </p> <p>My next-best alternative is to return a structure that has it's own IsCanceled property:</p> <p>(I've ignored some good coding and style practices for brevity here)</p> <pre><code>class MightBeCanceled&lt;T&gt; { public readonly T Value; public readonly bool IsCanceled; public MightBeCanceled(T value) { Value = value; IsCanceled = false; } public static MightBeCanceled&lt;T&gt; Canceled = new MightBeCanceled&lt;T&gt;(default(T), true); private MightBeCanceled(T value, bool isCanceled) { Value = value; IsCanceled = isCanceled; } } ... static async Task&lt;MightBeCanceled&lt;int&gt;&gt; Foo() { if (someCancellationCondition) return MightBeCanceled&lt;int&gt;.Canceled; else return new MightBeCanceled&lt;int&gt;(42); } static async void Bar() { var mightBeCanceled = await Foo(); if (mightBeCanceled.IsCanceled) ; // Take canceled action else ; // Take normal action } </code></pre> <p>But this seems redundant and harder to use. Not to mention it introduces consistency problems because there will be two IsCanceled's (one in the Task and one in the MightBeCanceled).</p>
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    1. COWho is canceling the Foo? It should only be cancellable by the caller, using a CancellationToken
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      1. USArne Claassen
 

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