Parallel.For and Task.CurrentID strange behavior

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I've discovered the following strange behavior for Parallel.For when option MaxDegreeOfParallelism is set.

I have the following program.

using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace CurrentId
{
    internal class Program
    {
        private static void Main(string[] args)
        {

            ParallelOptions po = new ParallelOptions();
            po.MaxDegreeOfParallelism = 3;

            Console.WriteLine("Parallel.For without delay.");
            Parallel.For(0, 19, po, i =>
            {
                Console.WriteLine("{0} on Task {1}", i, Task.CurrentId);
            });

            Console.WriteLine("Parallel.For with delay - Thread.Sleep.");
            Parallel.For(0, 19, po, i =>
            {
                Thread.Sleep(100);
                Console.WriteLine("{0} on Task {1}", i, Task.CurrentId);
            });

            Console.WriteLine("Press any key to exit.");
            Console.ReadLine();
        }
    }
}

While executing a program I get the following output. As you can see, when first Parallel.For is executing there are only three different kind task id = 1,2,3. But when the second Parallel.For is executing there are SIX different kind task id = 3,4,5,6,7,8. As I suppose the maximum count of different kind of task must correspond to the MaxDegreeOfParallelism option. I don't know how to deal with it. Any ideas?

asked 22 secs ago

Humpt

1

Parallel.For and Task.CurrentID strange behavior