儿童任务与等待

Question

当我可以让父任务等待它创建的所有任务时,我不确定创建子任务有什么好处.我运行以下代码,它在两种情况下产生相同的结果.

public static void Main(string[] args)
{
    RunWithChildren();
    RunWithWait();
}


private static void RunWithChildren()
{
    Task<Int32[]> parent = Task.Run(() =>
    {
        var results = new Int32[3];
        new Task(r => results[0] = 0, TaskContinuationOptions.AttachedToParent).Start();
        new Task(r => results[1] = 1, TaskContinuationOptions.AttachedToParent).Start();
        new Task(r => results[2] = 2, TaskContinuationOptions.AttachedToParent).Start();
        return results;
    });

    var finalTask = parent.ContinueWith(parentTask =>
    {
        foreach (int i in parentTask.Result)
            Console.WriteLine(i);
    });

    finalTask.Wait();
}


private static void RunWithWait()
{
    Task<Int32[]> parent = Task.Run(() =>
    {
        var results = new Int32[3];
        Task t1 = Task.Run(() => results[0] = 0);
        Task t2 = Task.Run(() => results[1] = 1);
        Task t3 = Task.Run(() => results[2] = 2);

        Task.WaitAll(t1, t2, t3);
        return results;
    });

    var finalTask = parent.ContinueWith(parentTask =>
    {
        foreach (int i in parentTask.Result)
            Console.WriteLine(i);
    });

    finalTask.Wait();
}

Answer 1

AttachedToParent为您提供了一种构建代码的不同方法.如果孩子Task可以在父母的代码中的不同位置开始Task,使用AttachedToParent意味着您不必担心将所有孩子Task收集到一个集合中.

在实践中,我认为这Task.WaitAll()更清楚,收集Task实际上并不是一个问题,所以我几乎从不使用AttachedToParent.