什么时候应该 TaskCompletionSource<T>使用? [英] When should TaskCompletionSource&lt;T&gt; be used?

问题描述

AFAIK，它只知道在某个时刻，它的 SetResult 或 SetException 方法被调用以完成 Task通过其 Task 属性公开.

AFAIK, all it knows is that at some point, its SetResult or SetException method is being called to complete the Task<T> exposed through its Task property.

换句话说，它充当Task及其完成的生产者.

In other words, it acts as the producer for a Task<TResult> and its completion.

我在这里看到了例子:

I saw here the example:

如果我需要一种方法来异步执行 Func 并有一个 Task表示该操作.

If I need a way to execute a Func<T> asynchronously and have a Task<T> to represent that operation.

public static Task<T> RunAsync<T>(Func<T> function) 
{ 
    if (function == null) throw new ArgumentNullException("function"); 
    var tcs = new TaskCompletionSource<T>(); 
    ThreadPool.QueueUserWorkItem(_ => 
    { 
        try 
        {  
            T result = function(); 
            tcs.SetResult(result);  
        } 
        catch(Exception exc) { tcs.SetException(exc); } 
    }); 
    return tcs.Task; 
}

如果我没有 Task.Factory.StartNew 可以使用 -但我确实有Task.Factory.StartNew.

Which could be used if I didn’t have Task.Factory.StartNew - But I do have Task.Factory.StartNew.

问题:

谁能通过例子解释一个直接与TaskCompletionSource相关的场景而不是我没有 Task.Factory.StartNew 的假设情况?

Can someone please explain by example a scenario related directly to TaskCompletionSource and not to a hypothetical situation in which I don't have Task.Factory.StartNew?

推荐答案

我主要在只有基于事件的 API 可用时使用它 (例如 Windows Phone 8 套接字):

I mostly use it when only an event based API is available (for example Windows Phone 8 sockets):

public Task<Args> SomeApiWrapper()
{
    TaskCompletionSource<Args> tcs = new TaskCompletionSource<Args>(); 

    var obj = new SomeApi();

    // will get raised, when the work is done
    obj.Done += (args) => 
    {
        // this will notify the caller 
        // of the SomeApiWrapper that 
        // the task just completed
        tcs.SetResult(args);
    }

    // start the work
    obj.Do();

    return tcs.Task;
}

所以当它与 C#5 async 关键字一起使用时特别有用.

So it's especially useful when used together with the C#5 async keyword.

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