c# - How to count the amount of concurrent threads in .NET application?

Question

Having read Parallel.ForEach keeps spawning new threads I am still in doubt whether it is a correct method of counting the number of concurrent there threads?

What I see is that method counts the number of simultaneously entered but not completed iterations (loops) in Parallel.ForEach.
Is it synonym of the number of concurrent threads conveying correct number of simultaneously run threads?
I'm not a specialist but I can imagine that:

• the threads can be re-used while its activity swapped somewhere for continuing later.
• theoretically the thread engaged for a loop activity is kept in thread pool after a loop completion but not re-used for another
• Or what are the possibilities of distorting the purity of experiment (of threads counting)?

Anyway, how to directly count the amount of running threads of .NET process, preferably in (C#) code?

Update:

So, if to follow the Jeppe Stig Nielsen's answer and use for count

directThreadsCount = Process.GetCurrentProcess().Threads.Count;

then output is, both in Release (threadsCount == 7) and Debug (threadsCount == 15) mode is very similar:

[Job 0 complete. 2 threads remaining but directThreadsCount == 7
[Job 1 complete. 1 threads remaining but directThreadsCount == 7
[Job 2 complete. 2 threads remaining but directThreadsCount == 7
[Job 4 complete. 2 threads remaining but directThreadsCount == 7
[Job 5 complete. 2 threads remaining but directThreadsCount == 7
[Job 3 complete. 2 threads remaining but directThreadsCount == 7
[Job 6 complete. 2 threads remaining but directThreadsCount == 7
[Job 9 complete. 2 threads remaining but directThreadsCount == 7
[Job 7 complete. 1 threads remaining but directThreadsCount == 7
[Job 8 complete. 0 threads remaining but directThreadsCount == 7
FINISHED

That is, the number of threads are not ever decreasing telling that the cited above method is incorrect while System.Diagnostics.ProcessThread gives "Class name is not valid at this point"

Are my conclusions correct and why cannot ProcessThread be used?

The used code of C# console application:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace Edit4Posting
{
public class Node
{

  public Node Previous { get; private set; }
  public Node(Node previous)
  {
    Previous = previous;
    }
  }
  public class Edit4Posting
  {

    public static void Main(string[] args)
    {
      int concurrentThreads = 0;
      int directThreadsCount = 0;
      int diagThreadCount = 0;

      var jobs = Enumerable.Range(0, 10);
      Parallel.ForEach(jobs, delegate(int jobNr)
      {
        int threadsRemaining = Interlocked.Increment(ref concurrentThreads);

        int heavyness = jobNr % 9;

        //Give the processor and the garbage collector something to do...
        List<Node> nodes = new List<Node>();
        Node current = null;
        //for (int y = 0; y < 1024 * 1024 * heavyness; y++)
        for (int y = 0; y < 1024 * 24 * heavyness; y++)
        {
          current = new Node(current);
          nodes.Add(current);
        }
        //*******************************
        //uncommenting next line gives: "Class name is not valid at this point"
        //diagThreadCount=System.Diagnostics.ProcessThread
        directThreadsCount = Process.GetCurrentProcess().Threads.Count;
        //*******************************
        threadsRemaining = Interlocked.Decrement(ref concurrentThreads);
        Console.WriteLine(
           "[Job {0} complete. {1} threads remaining but directThreadsCount == {2}",
            jobNr, threadsRemaining, directThreadsCount);
      });
      Console.WriteLine("FINISHED");
      Console.ReadLine();
    }
  }
}

Answer 1

There are different kinds of threads, I think. The operating system's threads for the application you're running, can be counted with:

int number = Process.GetCurrentProcess().Threads.Count;

It seems to count System.Diagnostics.ProcessThread instances. Maybe you need to count another kind of thread, like "managed threads", so I'm not sure my answer is what you seek.