Question

I have a collection which has elements to be processed and at max only four elements can be processed together. At run time all process started together and all goes in waiting state. Only four elements are processed at one time.

Problem is the processing elements are chosen randomly as all threads are waiting for resources to get free. Means first element can be the last one from collection.

But, I need to process elements in order they are in the collection.

Please tell me how can I achieve this?

I am using TPL and C# 4.0

Answer 1

This is how I acheived this task

public delegate void ProcessFinished(IParallelProcess process);
public interface IParallelProcess
{
    void Start();
    event ProcessFinished ProcessFinished;
}

public class ParallelProcessBasket : ConcurrentQueue<IParallelProcess>
{
    public void Put(IParallelProcess process)
    {
        base.Enqueue(process);
    }
    public IParallelProcess Get()
    {
        IParallelProcess process = null;
        base.TryDequeue(out process);
        return process;
    }
}
public class ParallelProcessor<T> where T : class
{
    private ParallelProcessBasket basket;
    private readonly int MAX_DEGREE_OF_PARALLELISM;
    private Action<T> action;
    public ParallelProcessor(int degreeOfParallelism, IEnumerable<IParallelProcess> processes, Action<T> action)
    {
        basket = new ParallelProcessBasket();
        this.action = action;
        processes.ToList().ForEach(
            (p) =>
            {
                basket.Enqueue(p);
                p.ProcessFinished += new ProcessFinished(p_ProcessFinished);
            });
        MAX_DEGREE_OF_PARALLELISM = degreeOfParallelism;
    }

    private void p_ProcessFinished(IParallelProcess process)
    {
        if (!basket.IsEmpty)
        {
            T element = basket.Get() as T;
            if (element != null)
            {
                Task.Factory.StartNew(() => action(element));
            }
        }
    }


    public void StartProcessing()
    {
        // take first level of iteration
        for (int cnt = 0; cnt < MAX_DEGREE_OF_PARALLELISM; cnt++)
        {
            if (!basket.IsEmpty)
            {
                T element = basket.Get() as T;
                if (element != null)
                {
                    Task.Factory.StartNew(() => action(element));
                }
            }
        }
    }
}
static void Main(string[] args)    
{
     ParallelProcessor<ParallelTask> pr = new ParallelProcessor<ParallelTask>(Environment.ProcessorCount, collection, (e) => e.Method1());
            pr.StartProcessing();
}

Thanks..