How to wrap ConcurrentDictionary in BlockingCollection?

Question

I try to implement a ConcurrentDictionary by wrapping it in a BlockingCollection but did not seem to be successful.

I understand that one variable declarations work with BlockingCollection such as ConcurrentBag<T>, ConcurrentQueue<T>, etc.

So, to create a ConcurrentBag wrapped in a BlockingCollection I would declare and instantiate like this:

BlockingCollection<int> bag = new BlockingCollection<int>(new ConcurrentBag<int>());

But how to do it for ConcurrentDictionary? I need the blocking functionality of the BlockingCollection on both the producer and consumer side.

Answer 1

Maybe you need a concurrent dictionary of blockingCollection

        ConcurrentDictionary<int, BlockingCollection<string>> mailBoxes = new ConcurrentDictionary<int, BlockingCollection<string>>();
        int maxBoxes = 5;

        CancellationTokenSource cancelationTokenSource = new CancellationTokenSource();
        CancellationToken cancelationToken = cancelationTokenSource.Token;

        Random rnd = new Random();
        // Producer
        Task.Factory.StartNew(() =>
        {
            while (true)
            {
                int index = rnd.Next(0, maxBoxes);
                // put the letter in the mailbox 'index'
                var box = mailBoxes.GetOrAdd(index, new BlockingCollection<string>());
                box.Add("some message " + index, cancelationToken);
                Console.WriteLine("Produced a letter to put in box " + index);

                // Wait simulating a heavy production item.
                Thread.Sleep(1000);
            }
        });

        // Consumer 1
        Task.Factory.StartNew(() =>
        {
            while (true)
            {
                int index = rnd.Next(0, maxBoxes);
                // get the letter in the mailbox 'index'
                var box = mailBoxes.GetOrAdd(index, new BlockingCollection<string>());
                var message = box.Take(cancelationToken);
                Console.WriteLine("Consumed 1: " + message);

                // consume a item cost less than produce it:
                Thread.Sleep(50);
            }
        });

        // Consumer 2
        Task.Factory.StartNew(() =>
        {
            while (true)
            {
                int index = rnd.Next(0, maxBoxes);
                // get the letter in the mailbox 'index'
                var box = mailBoxes.GetOrAdd(index, new BlockingCollection<string>());
                var message = box.Take(cancelationToken);
                Console.WriteLine("Consumed 2: " + message);

                // consume a item cost less than produce it:
                Thread.Sleep(50);
            }
        });

        Console.ReadLine();
        cancelationTokenSource.Cancel();

By this way, a consumer which is expecting something in the mailbox 5, will wait until the productor puts a letter in the mailbox 5.

Answer 2

You'll need to write your own adapter class - something like:

public class ConcurrentDictionaryWrapper<TKey,TValue>
    : IProducerConsumerCollection<KeyValuePair<TKey,TValue>>
{
    private ConcurrentDictionary<TKey, TValue> dictionary;

    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
    {
        return dictionary.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    public void CopyTo(Array array, int index)
    {
        throw new NotImplementedException();
    }

    public int Count
    {
        get { return dictionary.Count; }
    }

    public object SyncRoot
    {
        get { return this; }
    }

    public bool IsSynchronized
    {
        get { return true; }
    }

    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int index)
    {
        throw new NotImplementedException();
    }

    public bool TryAdd(KeyValuePair<TKey, TValue> item)
    {
        return dictionary.TryAdd(item.Key, item.Value);
    }

    public bool TryTake(out KeyValuePair<TKey, TValue> item)
    {
        item = dictionary.FirstOrDefault();
        TValue value;
        return dictionary.TryRemove(item.Key, out value);
    }

    public KeyValuePair<TKey, TValue>[] ToArray()
    {
        throw new NotImplementedException();
    }
}