How to deal with ThreadPool and member variables?

Question

Hello everyone,

I am a bit new to ThreadPool in .NET. I was wondering, if I can only send one object to my callback method, how am I able to access the class member variable to call its methods? (see customClass in CallBack())

And how would I load the data from customClass? Do I pass the customClass to a different CallBack method? is this approach alright?

As you can see it is a bit of lack of experience, so any tips along the way would really be appreciated.

Thank you, Kave

class Program
           {
                static void Main(string[] args)
                {
                    CustomClass customClass = new CustomClass();

                ThreadPool.QueueUserWorkItem(CallBack, "Hello"); 


                Console.Read();
            }

            private static void CallBack(object state)
            {
                customClass.SaveData(state.ToString());
            }
        }

Answer 1

The easiest way to do this is to use a closure to capture all the variables you want (i.e. use an anonymous method or a lambda expression). You need to be careful about exactly what's captured if you're using a loop, but it's handier than passing through an object and having to cast it back to the right type etc.

Answer 2

class Program
{
  static void Main(string[] args)
  {
    CustomClass customClass = new CustomClass();
    ThreadPool.QueueUserWorkItem(x => CallBack(customClass, "Hello")); 
    Console.Read();
  }

  private static void CallBack(CustomClass custom, string text)
  {
    customClass.SaveData(text);
  }
}

Answer 3

In addition to what has been said: If CustomClass is under your control and asynchronously invoking SaveData is a common use case, you could think about providing a SaveDataAsync method:

class CustomClass {

    public void SaveDataAsync(string path) {
        ThreadPool.QueueUserWorkItem(state => this.SaveData(path));
    }

    public void SaveData(string path) {
        ...
    }
}

See the Event-based Asynchronous Pattern.