Is it possible to execute two async methods in parallel?

Question

If I execute two tasks, I can execute the two tasks at the same time and wait until the two tasks are finished. With this code:

Task<bool> tsk01 = Task.Run(()=> my code; return true);
Task<bool> tsk02 = Task.Run(()=> my code; return true);
Task.WaitAll(tsk01, tsk02);

//next code

In this case the following code is only executed when all tasks are finished. But the application is not blocked.

However if I have this code:

private async void Button_Click_2(object sender, RoutedEventArgs e)
{
    Task<bool> tsk01 = miMetodoAsync01();
    Task<bool> tsk02 = miMetodoAsync02();
    Task.WaitAll(tsk01, tsk02);
}

private async Task<bool> miMetodoAsync02()
{
    return await TaskEx.Run<bool>(() =>
        {
            Int64 resultado = 0;
            for (Int64 i = 1; i < 1000000000; i++)
            {
                resultado = resultado + 1;
            }

            return true;

        }).ConfigureAwait(false);
    }



    private async Task<bool> miMetodoAsync01()
    {
        return await TaskEx.Run<bool>(() =>
        {
            Int64 resultado = 0;
            for (Int64 i = 1; i < 1000000000; i++)
            {
                resultado = resultado + 1;
            }

            return true;

        }).ConfigureAwait(false);
    }

In this second option the application is blocked because the WaitAll seems to wait for a response from the tasks that never happens.

Why in the first case the application is not blocked and in the second one it is?

I think that you are wrong. Task.WaitAll should block the thread. await Task.WhenAll(...) will not — George Mauer
– George Mauer, Commented Oct 21, 2014 at 17:58
I only have available Task.WaitAny and task.WaitAll. I don't have Task.WhenAll. — Álvaro García
– Álvaro García, Commented Oct 21, 2014 at 18:02
Task.WhenAll was added in .Net 4.5 along with async/await msdn.microsoft.com/en-us/library/hh160374(v=vs.110).aspx. — Preston Guillot
– Preston Guillot, Commented Oct 21, 2014 at 18:09

Stephen Cleary · Accepted Answer · 2014-10-21 18:11:47Z

4

Both your examples will block the UI thread. That's what Task.WaitAll means.

However, you can use TaskEx.WhenAll:

await TaskEx.WhenAll(tsk01, tsk02);

answered Oct 21, 2014 at 18:11

Stephen Cleary

460k78 gold badges721 silver badges858 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Scott · Accepted Answer · 2014-10-21 18:39:08Z

The method Task.WaitAll will block the UI thread as it waits for all tasks to return before continuing.

The code examples that you gave for creating a Task are basically the same (albeit written slightly different ways). Both the return Task<bool>.

The difference is the function being run inside both of your lambda expressions. Your first example has a "my code" reference and returns. The second example you created two counters.

If your "my code" is defined differently than the the counters created in the second example, or if you are only returning true in your lambda expression, then you will get the appearance of one waiting over the other.

Simply returning true will end the threads immediately after they are created. Where-as the counter takes time to compute (also depending on your CPU speed).

If you add the same counter into your function of the first example, you will find that both take the same time, and Task.WaitAllblocks your UI. You can use the System.Diagnositics.StopWatch class to time it.

    static void Main(string[] args)
    {
        string test = Console.ReadLine();

        System.Diagnostics.Stopwatch t = new System.Diagnostics.Stopwatch();
        t.Start();
        Task<bool> task1 = Task.Run<bool>(() => { return true; });
        Task<bool> task2 = Task.Run<bool>(() => { return true; });
        Task.WaitAll(task1, task2);
        t.Stop();

        Console.WriteLine("Elapsed time: " + t.Elapsed);

        System.Diagnostics.Stopwatch t2 = new System.Diagnostics.Stopwatch();
        t2.Start();
        Task<bool> task3 = asyncMethod1();
        Task<bool> task4 = asyncMethod2();
        Task.WaitAll(task3, task4);
        t2.Stop();

        Console.WriteLine("Elapsed time: " + t2.Elapsed);
        Console.Read();
    }

Collectives™ on Stack Overflow

Is it possible to execute two async methods in parallel?

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related