Running tasks in sequence inside an infinite loop

Question

I have a several tasks that are run in sequence; one after the other.

Task.Factory.StartNew(() => DoWork1())
            .ContinueWith((t1) => DoWork2())
            .ContinueWith(t2 => DoWork3());

I want to put this inside a loop so they run indefinitely (After DoWork3() is done, go back to DoWork1(). I tried putting inside a while loop, but the loop goes to the next iteration as soon the task is launched, creating a boatload of new tasks.

Would also be nice to have a way to exit condition to break out of the loop, maybe pass a cancellation token.

Thanks!

Ended up following @MickyD advise on using successive awaits and replaced the ContinueWith's. Either one works, but awaits seems to more readable / flexible. — user1957413, Mar 03 '18 at 03:28

score 2 · Accepted Answer · answered Mar 01 '18 at 05:29

The simplest way would be to use async/await:

async void DoStuff()
{
    while (true)
    {
        await Task.Factory.StartNew(() => DoWork1())
            .ContinueWith((t1) => DoWork2())
            .ContinueWith(t2 => DoWork3());
    }
}

Or you can call the method again after the last task is completed, simulating a while(true) :

void DoStuff()
{
    Task.Factory.StartNew(() => DoWork1())
        .ContinueWith((t1) => DoWork2())
        .ContinueWith(t2 => DoWork3())
        .ContinueWith(t3=> DoStuff());
}

You could also Wait for the task explicitly, but this will block the thread you are executing on:

void DoStuff()
{
    while (true)
    {
        Task.Factory.StartNew(() => DoWork1())
            .ContinueWith((t1) => DoWork2())
            .ContinueWith(t2 => DoWork3())
            .Wait();
    }
}

score 1 · Answer 2 · answered Mar 01 '18 at 05:29

1

You can wait for the task to complete before starting the next iteration of while loop.

while(true) 
{
    var task = Task.Factory.StartNew(() => DoWork1())
            .ContinueWith((t1) => DoWork2())
            .ContinueWith(t2 => DoWork3());
    task.Wait(); 
}

Without task.Wait() (or a similar mechanism) the tasks will be scheduled to run, but the next iteration of while loop will begin without waiting for these tasks to complete.

answered Mar 01 '18 at 05:29

Nisarg Shah

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Though nice, in this day and age successive inline `await`s are kinder to kittens than `.ContinueWith()` – Mar 01 '18 at 05:33
@MickyD how would you write the above using inline awaits? I'd like to know! – user1957413 Mar 01 '18 at 05:57
`await Task.Run(() => DoWork()); await Task.Run(() => DoWork2()); await Task.Run(() => DoWork());` Not hard. Also [check out the dangers](https://stackoverflow.com/a/36798058/585968) of `ContinueWith` – Mar 01 '18 at 07:12

score 0 · Answer 3 · answered Mar 01 '18 at 05:38

You can do something as follows:

List<Task> tasks = new List<Task>();

for (int i = 0; i < 10; i++) //your loop
{
    var task = Task.Factory.StartNew(() => DoWork1()).ContinueWith((t1) => DoWork2()).ContinueWith(t2 => DoWork3());
    tasks.Add(task);
}

Task.WaitAll(tasks.ToArray());

Running tasks in sequence inside an infinite loop

3 Answers3

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