Maximum number of threads in a .NET app?


Question

What is the maximum number of threads you can create in a C# application? And what happens when you reach this limit? Is an exception of some kind thrown?

1
127
7/4/2009 11:08:03 PM

Accepted Answer

There is no inherent limit. The maximum number of threads is determined by the amount of physical resources available. See this article by Raymond Chen for specifics.

If you need to ask what the maximum number of threads is, you are probably doing something wrong.

[Update: Just out of interest: .NET Thread Pool default numbers of threads:

  • 1023 in Framework 4.0 (32-bit environment)
  • 32767 in Framework 4.0 (64-bit environment)
  • 250 per core in Framework 3.5
  • 25 per core in Framework 2.0

(These numbers may vary depending upon the hardware and OS)]

137
8/13/2019 2:56:55 PM

Mitch is right. It depends on resources (memory).

Although Raymond's article is dedicated to Windows threads, not to C# threads, the logic applies the same (C# threads are mapped to Windows threads).

However, as we are in C#, if we want to be completely precise, we need to distinguish between "started" and "non started" threads. Only started threads actually reserve stack space (as we could expect). Non started threads only allocate the information required by a thread object (you can use reflector if interested in the actual members).

You can actually test it for yourself, compare:

    static void DummyCall()
    {
        Thread.Sleep(1000000000);
    }

    static void Main(string[] args)
    {
        int count = 0;
        var threadList = new List<Thread>();
        try
        {
            while (true)
            {
                Thread newThread = new Thread(new ThreadStart(DummyCall), 1024);
                newThread.Start();
                threadList.Add(newThread);
                count++;
            }
        }
        catch (Exception ex)
        {
        }
    }

with:

   static void DummyCall()
    {
        Thread.Sleep(1000000000);
    }

    static void Main(string[] args)
    {
        int count = 0;
        var threadList = new List<Thread>();
        try
        {
            while (true)
            {
                Thread newThread = new Thread(new ThreadStart(DummyCall), 1024);
                threadList.Add(newThread);
                count++;
            }
        }
        catch (Exception ex)
        {
        }
    }

Put a breakpoint in the exception (out of memory, of course) in VS to see the value of counter. There is a very significant difference, of course.


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