Task Parallel Library - Know when all tasks are finished - c#-4.0

Question

I use Task Parallel Library to start some tasks, like so:
public static void Main()
{
for (var i = 0; i < 10; i++)
{
var x = i;
Task.Factory.StartNew(() => new WorkerClass(x).Do());
}
// (*) Here I'd like to wait for all tasks to finish
Task.WaitAll();
Console.WriteLine("Ready.");
Console.ReadLine();
}
The problem is that some tasks can create new tasks themselves. This is how WorkerClass looks like:
public class WorkerClass
{
private static readonly NLog.Logger Log = NLog.LogManager.GetCurrentClassLogger();
private readonly int _i;
public WorkerClass(int i)
{
_i = i;
}
public void Do()
{
if (_i % 3 == 0)
Task.Factory.StartNew(() => new WorkerClass(_i + 101).Do());
Log.Info("Started {0}", _i);
Thread.Sleep(2000);
Log.Info("Done {0}", _i);
}
}
For every value of i that's a multiple of 3, a new Task is started.
I'd like to be able to wait until all tasks (including the ones created by other tasks) are finished.
Is there a clean/built-in way to do this (with or without TPL)?

Answer 1

Keep a reference to all top-level tasks and then just use WaitAll:
var tasks = new Task[10];
for (var i = 0; i < 10; i++)
{
var x = i;
tasks[i] = Task.Factory.StartNew(() => new WorkerClass(x).Do());
}
Task.WaitAll( tasks );
As for the child tasks, just make sure you attach them to the parent task. This means that the parent task will not go into a complete state until all child tasks are also finished.
Task.Factory.StartNew(() => { }, TaskCreationOptions.AttachedToParent);