C# - Linq MultiThreading with varying Max/Min Threads?

Question

ThreadPool.SetMinThreads(50, 50);
ServicePointManager.MaxServicePointIdleTime = 8000;
ServicePointManager.DefaultConnectionLimit = 50;

List<Match> Combos = new Regex("^(.{5,}):(.{6,})$", RegexOptions.Multiline).Matches(File.ReadAllText(ofd.FileNames[0])).OfType<Match>().ToList();
var query = Combos.ToObservable().SelectMany(s => Observable.Start(() => new
{
    grab = checkall(s.Groups[1].Value.Replace("\n", "").Replace("\r", ""), s.Groups[2].Value.Replace("\n", "").Replace("\r", ""))
})).ObserveOn(this).Do(x =>
{
    try
    {
        TotalChecked.Text = "Tested: " + (int.Parse(TotalChecked.Text.Substring(7)) + 1).ToString();
        progressBar2.Value = (int)Math.Round((double)(100 * int.Parse(TotalChecked.Text.Substring(7))) / Combos.Count);
    }
    catch (Exception)
    {
        TotalChecked.Text = "Tested: " + (int.Parse(TotalChecked.Text.Substring(7)) + 1).ToString();
        progressBar2.Value = (int)Math.Round((double)(100 * int.Parse(TotalChecked.Text.Substring(7))) / Combos.Count);
    }
});
query.ToArray().ObserveOn(this).Subscribe(x =>
{
    CheckButton.Location = new Point(CheckButton.Location.X + 31, 9);
    CheckButton.Width -= 31;
});

The code above uses regex on a text file and then executes a function. It works just fine, but now I want it to execute multiple DIFFERENT functions and only allow a set amount of threads on some of them.

For example:

var query = Combos.ToObservable().SelectMany(s => Observable.Start(() => new
{
    grab = checkall(s.Groups[1].Value.Replace("\n", "").Replace("\r", ""), s.Groups[2].Value.Replace("\n", "").Replace("\r", "")),
    //This one should be LIMITED to only 5 threads MAX!
    grab2 = checktwo(Hi, Hello)
}))

In the code above I added grab2 which should have a maximum of 5 threads allocate to it.

To be honest I have no idea how I could execute a method like this. Any help would be appreciated.

Answer 1

If you need to some code gets executed only by n threads, you need a semaphore , in this case SemaphoreSlim is enough

// 5 threads to run in parallel, all 5 can start immidiately
var semaphore = new SemaphoreSlim(5, 5);

// ...

try
{
    semaphore.Wait();
    //This one should be LIMITED to only 5 threads MAX!
    grab2 = checktwo(Hi, Hello);
}
finally
{
    // ensure the release of semaphore
    semaphore.Release();
}

You can even wait for it in async methods :

await semaphore.WaitAsync();