Parallel.For() Not Async Friendly

Parallel.For.Async.cs

using System.Threading.Tasks

void Main()
{	
	var options = new ParallelOptions() {
		MaxDegreeOfParallelism = 2
	};
	
	Parallel.For(0, 10, options, i => ExecTaskSync(i));
	
	Parallel.For(0, 10, options, async i => await ExecTask(i));
	
	Console.WriteLine("ALL DONE.");
}

// Define other methods and classes here

async Task<int> ExecTask(int index)
{
	Console.WriteLine($"Task {index} starting.");
	await Task.Delay(1000);
	Console.WriteLine($"Task {index} done.");
	
	return index;
}

int ExecTaskSync(int index)
{
	Console.WriteLine($"Sync Task {index} starting.");
	Thread.Sleep(1000);
	Console.WriteLine($"Sync Task {index} done.");

	return index;
}


/**********  
* OUTPUT  *
***********
Sync Task 0 starting.
Sync Task 5 starting.
Sync Task 0 done.
Sync Task 1 starting.
Sync Task 5 done.
Sync Task 6 starting.
Sync Task 6 done.
Sync Task 7 starting.
Sync Task 1 done.
Sync Task 2 starting.
Sync Task 2 done.
Sync Task 3 starting.
Sync Task 7 done.
Sync Task 8 starting.
Sync Task 3 done.
Sync Task 8 done.
Sync Task 9 starting.
Sync Task 4 starting.
Sync Task 4 done.
Sync Task 9 done.
Task 0 starting.
Task 5 starting.
Task 1 starting.
Task 6 starting.
Task 7 starting.
Task 8 starting.
Task 9 starting.
Task 3 starting.
Task 4 starting.
Task 2 starting.
ALL DONE.
Task 2 done.
Task 4 done.
Task 9 done.
Task 0 done.
Task 8 done.
Task 3 done.
Task 7 done.
Task 5 done.
Task 6 done.
Task 1 done.

*/