等待单个任务从List< Task<.>中失败.更干净，可能与LINQ有关? [英] Waiting for a single task to fail out of a List<Task<..>> more cleanly, possibly with LINQ?

问题描述

在我的应用程序中，我有一个List<Task<Boolean>>，我可以通过Task.Wait[..]来确定它们是否成功完成(Result = true).虽然如果在等待期间Task完成并返回了falsey值，但是我想取消所有其他Task，则我正在等待并基于此进行操作.

In my application I have a List<Task<Boolean>> that I Task.Wait[..] on to determine if they completed successfully (Result = true). Though if during my waiting a Task completes and returns a falsey value I want to cancel all other Task I am waiting on and do something based on this.

我创建了两个丑陋"的方法来实现这一目的

I have created two "ugly" methods to do this

// Create a CancellationToken and List<Task<..>> to work with
CancellationToken myCToken = new CancellationToken();
List<Task<Boolean>> myTaskList = new List<Task<Boolean>>();

//-- Method 1 --
    // Wait for one of the Tasks to complete and get its result
Boolean finishedTaskResult = myTaskList[Task.WaitAny(myTaskList.ToArray(), myCToken)].Result;

    // Continue waiting for Tasks to complete until there are none left or one returns false
    while (myTaskList.Count > 0 && finishedTaskResult)
    {
        // Wait for the next Task to complete
        finishedTaskResult = myTaskList[Task.WaitAny(myTaskList.ToArray(), myCToken)].Result;
        if (!finishedTaskResult) break;
    }
    // Act on finishTaskResult here

// -- Method 2 -- 
    // Create a label to 
    WaitForOneCompletion:
    int completedTaskIndex = Task.WaitAny(myTaskList.ToArray(), myCToken);

    if (myTaskList[completedTaskIndex].Result)
    {
        myTaskList.RemoveAt(completedTaskIndex);
        goto WaitForOneCompletion;
    }
    else
        ;// One task has failed to completed, handle appropriately 

我想知道是否有更清洁的方法(可能与LINQ一起使用)?

I was wondering if there was a cleaner way to do this, possibly with LINQ?

推荐答案

您可以使用以下方法来执行一系列任务，并创建一个新的任务序列，这些任务序列代表初始任务，但以它们全部完成的顺序返回:

You can use the following method to take a sequence of tasks and create a new sequence of tasks that represents the initial tasks but returned in the order that they all complete:

public static IEnumerable<Task<T>> Order<T>(this IEnumerable<Task<T>> tasks)
{
    var taskList = tasks.ToList();

    var taskSources = new BlockingCollection<TaskCompletionSource<T>>();

    var taskSourceList = new List<TaskCompletionSource<T>>(taskList.Count);
    foreach (var task in taskList)
    {
        var newSource = new TaskCompletionSource<T>();
        taskSources.Add(newSource);
        taskSourceList.Add(newSource);

        task.ContinueWith(t =>
        {
            var source = taskSources.Take();

            if (t.IsCanceled)
                source.TrySetCanceled();
            else if (t.IsFaulted)
                source.TrySetException(t.Exception.InnerExceptions);
            else if (t.IsCompleted)
                source.TrySetResult(t.Result);
        }, CancellationToken.None, TaskContinuationOptions.PreferFairness, TaskScheduler.Default);
    }

    return taskSourceList.Select(tcs => tcs.Task);
}

现在，您可以根据任务的完成顺序对任务进行排序了，您可以基本上完​​全按照您的要求编写代码:

Now that you have the ability to order the tasks based on their completion you can write the code basically exactly as your requirements dictate:

foreach(var task in myTaskList.Order())
    if(!await task)
        cancellationTokenSource.Cancel();

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