Threading issue: locking data [modified]

Kelsen

I'm new to C# threads and I was trying to populate a list with a series of threads but my list is not being populated after the threads finish. Some code might help describe my situation: NOTE: I have left some methods out but I don't believe that will be an issue.

public class ManagerClass {
  private List<BeanType> beans = new List<BeanType>();
  private static Object lockObj = new Object();
  private static readonly int MAX_THREADS = 5;

  public List<BeanType> getBeans() {
    string[] keys = null;

    keys = getKeys();
    ThreadPool.SetMaxThreads(MAX_THREADS, MAX_THREADS);

    foreach (string key in keys) {
      ThreadPool.QueueUserWorkItem(new WaitCallback(getValueThreaded), key);
    }
    // Assuming 10000 is enough time for the threads to finish.
    Thread.Sleep(10000);
    Console.WriteLine(beans.Capacity);
    return beans;
  }

  public void getValueThreaded(object obj) {
    string key = (string)obj;
    string value = getValue(key);

    lock(lockObj) {
      beans.Add(new BeanType(key, value));
    }
  }
}

That is the jist of it. BeanType is an arbitrary type for the sake of this example. In the console the list prints out a capacity of 0 every time. Can anyone explain this? -- modified at 11:20 Tuesday 6th March, 2007 -- modified at 12:24 Tuesday 6th March, 2007

Kelsen

Leslie Sanford

foreach (string key in keys) {
ThreadPool.QueueUserWorkItem(new WaitCallback(getValueThreaded), key);
}
Console.WriteLine(beans.Capacity);

Kelsen wrote:

In the console the list prints out a capacity of 0 every time. Can anyone explain this?

Could it be that the console prints out before the thread pool items have a chance to run?

Kelsen

Leslie Sanford wrote:

Could it be that the console prints out before the thread pool items have a chance to run?

I migrated the WriteLine outside of the method and it still outputs 0. The code looks like:

public class SomeClass {
  private static ManagerClass manager = new ManagerClass();

  public static void Main() {
    List beans = manager.getBeans();
    Console.WriteLine(beans.Capacity);
  }
}

I also placed a wait at the end of the getBeans method. Any ideas?

Kelsen

led mike

Kelsen wrote:

but my list is not being populated after the threads finish.

Kelsen wrote:

Can anyone explain this?

The threads are NOT "finished" after they are "queued", they are ummmm... queued.

led mike

Kelsen

led mike wrote:

The threads are NOT "finished" after they are "queued", they are ummmm... queued.

After the foreach completes and finishes waiting the threads should have finished executing. An example I wrote prior to posting this question was:

    public class ThreadTest
    {
        private static readonly int MAX_THREADS = 5;

        public static void Main()
        {
            ThreadPool.SetMaxThreads(MAX_THREADS, MAX_THREADS);
            for (int i = 0; i < 20; i++)
                ThreadPool.QueueUserWorkItem(new WaitCallback(processThread), (i + 1));
            Thread.Sleep(25000);
            Console.WriteLine("Finished!");
        }

        static void processThread(object obj)
        {
            Console.WriteLine("Thread " + (int)obj + " executing.");
            Thread.Sleep(5000);
        }
    }

This is of course assuming the Thread.Sleep(25000) will be long enough for the last 5 threads to execute. In my original post I didn't show my Thread.Sleep() but it was there within my code. I'll better document that to help clear up any confusion.

Kelsen

Kelsen

led mike wrote:

The threads are NOT "finished" after they are "queued", they are ummmm... queued.

Yup. Figured it out.

Kelsen