How to cancel Parallel.ForEach

static void Main(string[] args)
{
    List<RandomWait> waiters = new List<RandomWait>();
    for (int i = 0; i < 1000; i++)
    {
        waiters.Add(new RandomWait());
    }

    int counter = 0;

    ParallelOptions options = new ParallelOptions();
    CancellationTokenSource cancelToken = new CancellationTokenSource();
    options.MaxDegreeOfParallelism = 15;
    options.CancellationToken = cancelToken.Token;

    Task.Factory.StartNew(() =>
        {
            Parallel.ForEach(waiters, options,
                (waiter) =>
                {
                    counter++;
                    Console.WriteLine(counter);
                    waiter.Pause();
                    counter--;
                    Console.WriteLine(counter);
                });
        });

    Console.ReadLine();
    cancelToken.Cancel();
    Console.ReadLine();
}

public class RandomWait
{
    public void Pause()
    {
        Random rnd = new Random();
        Thread.Sleep(rnd.Next(2000));
    }
}