WaitAll与WhenAll

| 异步CTP中的Task.WaitAll()和Task.WhenAll()有什么区别？您能否提供一些示例代码来说明不同的用例？

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4 个回复

Task.WaitAll阻塞当前线程，直到一切完成。 Task.WhenAll返回一个任务，代表等待一切完成的动作。这意味着从异步方法中，您可以使用：

await Task.WhenAll(tasks);

...这意味着您的方法将在所有步骤完成后继续，但是您不会在此之前一直挂起一个线程。

吠强祷豪硅

尽管JonSkeet的答案以一种典型的出色方式为我解释了这种差异，但最大的实际差异是异常处理。编辑：同意-这不是最大的实际差异，而是差异。当任何任务抛出时，2ѭ将抛出an6ѭ，您可以检查所有抛出的异常。 await Task.WhenAll中的await解开AggregateException，并且“返回”只是第一个例外。当下面的程序以“ 10”执行时，输出如下。

19/11/2016 12:18:37 AM: Task 1 started
19/11/2016 12:18:37 AM: Task 3 started
19/11/2016 12:18:37 AM: Task 2 started
Caught Exception in Main at 19/11/2016 12:18:40 AM: Task 1 throwing at 19/11/2016 12:18:38 AM
Done.

当使用Task.WaitAll(taskArray)执行以下程序时，输出如下。

19/11/2016 12:19:29 AM: Task 1 started
19/11/2016 12:19:29 AM: Task 2 started
19/11/2016 12:19:29 AM: Task 3 started
Caught AggregateException in Main at 19/11/2016 12:19:32 AM: Task 1 throwing at 19/11/2016 12:19:30 AM
Caught AggregateException in Main at 19/11/2016 12:19:32 AM: Task 2 throwing at 19/11/2016 12:19:31 AM
Caught AggregateException in Main at 19/11/2016 12:19:32 AM: Task 3 throwing at 19/11/2016 12:19:32 AM
Done.

该程序：

class MyAmazingProgram
{
    public class CustomException : Exception
    {
        public CustomException(String message) : base(message)
        { }
    }

    static void WaitAndThrow(int id, int waitInMs)
    {
        Console.WriteLine($\"{DateTime.UtcNow}: Task {id} started\");

        Thread.Sleep(waitInMs);
        throw new CustomException($\"Task {id} throwing at {DateTime.UtcNow}\");
    }

    static void Main(string[] args)
    {
        Task.Run(async () =>
        {
            await MyAmazingMethodAsync();
        }).Wait();

    }

    static async Task MyAmazingMethodAsync()
    {
        try
        {
            Task[] taskArray = { Task.Factory.StartNew(() => WaitAndThrow(1, 1000)),
                                 Task.Factory.StartNew(() => WaitAndThrow(2, 2000)),
                                 Task.Factory.StartNew(() => WaitAndThrow(3, 3000)) };

            Task.WaitAll(taskArray);
            //await Task.WhenAll(taskArray);
            Console.WriteLine(\"This isn\'t going to happen\");
        }
        catch (AggregateException ex)
        {
            foreach (var inner in ex.InnerExceptions)
            {
                Console.WriteLine($\"Caught AggregateException in Main at {DateTime.UtcNow}: \" + inner.Message);
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($\"Caught Exception in Main at {DateTime.UtcNow}: \" + ex.Message);
        }
        Console.WriteLine(\"Done.\");
        Console.ReadLine();
    }
}