Task.WhenAll(taskList).Wait()是否与Task.WaitAll(taskList)相同？

Question

这些行的行为是否完全相同(包括通过AggregateException的exactly处理)？

Task.WhenAll(taskList).Wait()
Task.WaitAll(taskList)

谢谢

Answer 1

让我们通过实验来找到答案：

var task1 = Task.FromResult(13);
var task2 = Task.FromCanceled<int>(new CancellationToken(true));
var task3 = Task.FromCanceled<int>(new CancellationToken(true));
var task4 = Task.FromException<int>(new ApplicationException());
var task5 = Task.FromException<int>(new OverflowException());
Test("Successful+Canceled+Canceled", new[] { task1, task2, task3 });
Test("Successful+Failed+Failed", new[] { task1, task4, task5 });
Test("Successful+Canceled+Failed+Failed", new[] { task1, task2, task4, task5 });
Test("Successful+Canceled+Canceled+Failed", new[] { task1, task2, task3, task4 });

static void Test(string title, Task<int>[] tasks)
{
    Console.WriteLine();
    Console.WriteLine(title);
    try { Task.WaitAll(tasks); }
    catch (AggregateException ex)
    {
        Console.WriteLine($"WaitAll():      {ToString(ex)}");
    }
    try { Task.WhenAll(tasks).Wait(); }
    catch (AggregateException ex)
    {
        Console.WriteLine($"WhenAll.Wait(): {ToString(ex)}");
    }
}

static string ToString(AggregateException aex) {
    return $"({aex.InnerExceptions.Count}) " +
        String.Join(", ", aex.InnerExceptions.Select(ex => ex.GetType().Name));
}

输出：

Successful+Canceled+Canceled
WaitAll():      (2) TaskCanceledException, TaskCanceledException
WhenAll.Wait(): (1) TaskCanceledException

Successful+Failed+Failed
WaitAll():      (2) ApplicationException, OverflowException
WhenAll.Wait(): (2) ApplicationException, OverflowException

Successful+Canceled+Failed+Failed
WaitAll():      (3) TaskCanceledException, ApplicationException, OverflowException
WhenAll.Wait(): (2) ApplicationException, OverflowException

Successful+Canceled+Canceled+Failed
WaitAll():      (3) TaskCanceledException, TaskCanceledException, ApplicationException
WhenAll.Wait(): (1) ApplicationException

Try it on Fiddle。

我们所看到的是，Task.WaitAll()方法按原样传播任务的异常，而Task.WhenAll().Wait()方法仅传播单个TaskCanceledException，并且仅当没有其他类型的异常发生时才传播。

还应该提到的是，使用Task.WaitAll可以获得更多开箱即用的选项，比如millisecondsTimeout、cancellationToken，或者两者兼而有之。