Question

I’m experiencing a strange issue in a console application (unsure if this has something to do with it) and using Tasks.

Most examples show purposely invoking an Exception to test/explain the concept of WaitAll – but in my case, it seems I’m doing something fundamentally wrong (or don’t fully understand).

Task<int> task1 = Task<int>.Factory.StartNew(()=> foo(arg));
Task<int> task2 = Task<int>.Factory.StartNew(()=> bar(arg));

Task<int>[] tasks = {task1, task2};

try
{
    Task.WaitAll(tasks); //hits this far

     if((int)task1.Result * (int)task2.Result == 99) //this seems to never get hit
     {
         System.Environment.Exit(0); //so this isn't called             
     }
     else
     {
         System.Environment.Exit(1); // neither is this called
     }
 }
 catch
 {
     .....

In the above it seems that the if block isn’t hit so neither Exit Codes are returned – the console app therefore hangs.

No exception is thrown either – I can confirm this because all the tasks are in fact completed – I just didn’t include the catch section above for brevity.

The tasks are completed quickly – they’re not hanging so its not as if Task.WaitAll is still waiting – or perhaps it is, and that’s something I’m missing (what is it waiting for)?

Any thoughts, advice or brutal corrections? Thanks!

Answer 1

Just for the sake of argument I did a little test (shown below) – it demonstrates one of your tasks is hanging, and not returning a value.

        Task<int> task1 = Task<int>.Factory.StartNew(() =>
        {
            Thread.Sleep(2000);
            return 10;
        });
        Task<int> task2 = Task<int>.Factory.StartNew(() => 15);
        Task<int>[] tasks = {task1, task2};
        try
        {
            Stopwatch sw = new Stopwatch();
            sw.Start();
            Task.WaitAll(tasks);
            sw.Stop();
            Console.WriteLine(String.Format("tasks completed in {0}ms", sw.ElapsedMilliseconds));
        }
        catch
        {
            Console.WriteLine("Error");
        }
        Console.ReadLine();

If you run that, it will print tasks completed in 2000ms (give or take a few milliseconds). All I did was copy/paste your code and add in my own tasks.

So where you say "The tasks are [...] not hanging..." that is false – they must be hanging.