Using Task.Wait() for waiting while task is finished (even if it already finished)

Question

Can I use task.Wait(); like that? Note that when I call task.Wait the task is probably already finished.

And probably you can suggest better pattern.

class A {
    private Task task1;
    private Task task2;

    ...
    public void Connect() {
        stayConnected = true;
        task1 = Task.Factory.StartNew(....,
            while (stayConnected) {
                ....
            }
            LongRunning);
        task2 = Task.Factory.StartNew(....,
            while (stayConnected) {
                ....
            }
            LongRunning);
    }

    private volatile bool stayConnected;

    // should be synchronous. when return everything should be disconected
    public void Disconnect() {
        stayConnected = false;
        task1.Wait();
        task1 = null;
        task2.Wait();
        task2 = null;
    }

}

Answer 1

You can use a CancellationToken and Task.WaitAll(...) to do this...

public class A
{
    private readonly CancellationTokenSource tokenSource = new CancellationTokenSource();
    private Task task1;
    private Task task2;

    public void Connect()
    {
        task1 = Task.Factory.StartNew(SomeWork, tokenSource.Token);
        task2 = Task.Factory.StartNew(SomeWork, tokenSource.Token);
    }

    public void Disconnect()
    {
        tokenSource.Cancel();
        Task.WaitAll(task1,task2);
    }

    public void SomeWork(object o)
    {
        CancellationToken token = (CancellationToken)o;
        while (!token.IsCancellationRequested)
        {
            Console.WriteLine("working...");
        }
    }
}

For more information on managed threads check this and this article on MSDN. Enjoy :D

Answer 2

Task.Wait() should just return true if the task is completed, so sure you can. However, you should better use waiting with timeout or TimeSpan parameter if you have actions inside of while { } loop that can possibly cause a freeze.

Answer 3

This seems like a reasonable approach to me. You could improve it a bit by using Task.WaitAll() but that won't change much.

Also, I wouldn't set the fields to null unless I had good reason to do it. Yeah, those Tasks are not useful for anything anymore, but they are also almost free.