How to detect Tasks in a cycle

Question

class Program
{
    private static Task[] tasks;

    static void Main(string[] args)
    {
        tasks = new Task[]
        {
            new Task(() => Task.WaitAll(tasks[1])),
            new Task(() => Task.WaitAll(tasks[2])),
            new Task(() => Task.WaitAll(tasks[0])),
        };

        tasks[0].Start();
        tasks[1].Start();
        tasks[2].Start();

        Console.WriteLine(Task.WaitAll(tasks, 5000));
        Console.ReadLine();
    }
}

In the code sample above, I have set up three tasks "a", "b", "c" where "a" waits on "b" waits on "c" waits on "a".

Clearly, the WaitAll then returns false, since it is impossible for all tasks to complete.

My question is - is there any way, using Task Parallel Library, to detect the situation where Tasks are waiting in a cycle and, preferably, disallow it?

(This is to allow us to detect cyclic regions through reusing existing tasks)

@i3arnon - just because its closer to what we are doing in reality - this is obviously very cut down! — Fergus Bown, Apr 07 '15 at 15:52
Are you looking for compile time detection or run time dectection? Also what version of Visual Studio are you using (the options available to you may differ). — Scott Chamberlain, Apr 07 '15 at 16:37
@Scott it would be at runtime, in reality we wouldn't be adding tasks statically, they would vary based on many factors — Fergus Bown, Apr 07 '15 at 16:58

score 1 · Answer 1 · edited May 23 '17 at 10:24

1

You need to look into directed graphs and strongly connected component.

You could build a graph of your Tasks as you instantiate them and then compute the strongly connected components. For that you could use Tarjan's algorithm, here is an implementation in C#.

Or you could use a library like Quickgraph which handle that.

edited May 23 '17 at 10:24

Community

1
1

answered Apr 08 '15 at 08:15

Nicolas C

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How to detect Tasks in a cycle

1 Answers1