ActiveX objects and the .NET Garbage Collector

Question

I have a problem with multithreading in .net. With the following code:

class Program
{
    private static ManualResetEvent[] resetEvents;

    private void cs(object o)
    {
        int xx = 0;
        while (true)
        {
            xx++;
            System.Xml.XmlDocument document = new System.Xml.XmlDocument();
            document.Load("ConsoleApplication6.exe.config");

            MSScriptControl.ScriptControlClass s = 
                newMSScriptControl.ScriptControlClass();
            s.Language = "JScript";
            object res = s.Eval("1+2");
            Console.WriteLine("thread {0} execution {1}" , o , xx);
            System.Threading.Thread.Sleep(5000);
        }

    }
    static void Main(string[] args)
    {
        Program c = new Program();
        for (int i = 0; i < 1000; i++)
        {
            System.Threading.Thread t = new System.Threading.Thread(
                new System.Threading.ParameterizedThreadStart(c.cs));
            t.Start((object)i);
        }
    }
}

When this code executed, it crashes after some minutes. Why is it crashing? What can I do to prevent the crashes?

Answer 1

You're starting 1000 threads. That is 1000 MB in stack space alone plus all the objects the threads create. My guess is that you're running out of memory. What are you trying to accomplish?

Answer 2

It rarely makes sense to create more threads than processor cores b/c the app will spend alot of time context switching and you will not see much if any performance gain. The only number of threads that will run at the same time equals the number of cores your machine has. Why does this have to be done with 1000 threads? (Obviously I am assuming you don't have a 1000 core machine)

Answer 3

There are probably some aspects of this app that aren't apparent given the provided code. That being said, I haven't been able to reproduce the crash but I am able to run up an obscene amount of memory usage (160MB at 29 "xx++"s).

I suspect that the ScriptControlClass is staying alive in memory. While there may be better ways of solving this problem, I was able to keep the memory at a consistent 60-70MB with this addition:

Console.WriteLine("thread {0} execution {1}" , o , xx);
s = null;

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UPDATE
I had similar results with this code memory-wise but the code below was slightly faster. After several minutes the memory usage was a consistent 51MB when xx < 30 was changed back to true.

class Program
{
    private static ManualResetEvent[] resetEvents;

    [ThreadStatic]
    static ScriptControlClass s;

    private void cs(object o)
    {
        int xx = 0;

        if (s == null)
        {
            s = new ScriptControlClass();
        }

        /* you should be able to see consistent memory usage after 30 iterations */
        while (xx < 30)
        {
            xx++;

            //Unsure why this is here but doesn't seem to affect the memory usage
            //  like the ScriptControlClass object.
            System.Xml.XmlDocument document = new System.Xml.XmlDocument();
            document.Load("ConsoleApplication6.exe.config");

            s.Language = "JScript";
            object res = s.Eval("1+2");
            Console.WriteLine("thread {0} execution {1}", o, xx);

            System.Threading.Thread.Sleep(5000);
        }

        s = null;

    }
    static void Main(string[] args)
    {
        Program c = new Program();
        for (int i = 0; i < 1000; i++)
        {
            System.Threading.Thread t = new System.Threading.Thread(
                new System.Threading.ParameterizedThreadStart(c.cs));
            t.Start((object)i);
        }
    }
}

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UPDATE 2
My Googling can't find anything about using the ScriptControlClass in a multithreaded environment.