Checking a Queue Continuously

Question

I would like a function to check a Queue for new additions continuously on one thread

Obviously there is the option of a continuous loop with sleeps, but I want somethin

Answer 1

Try the blocking queue: Creating a blocking Queue<T> in .NET?

The basic idea is that when you call TryDequeue it will block until there is something in the queue. As you can see "beauty" of the blocking queue is that you don't have to poll/sleep or do anything crazy like that... it's the fundamental backbone for a Producer/Consumer pattern.

My version of the blocking queue is:

public class BlockingQueue<T> where T : class
{
    private bool closing;
    private readonly Queue<T> queue = new Queue<T>();

    public int Count
    {
        get
        {
            lock (queue)
            {
                return queue.Count;
            }
        }
    }

    public BlockingQueue()
    {
        lock (queue)
        {
            closing = false;
            Monitor.PulseAll(queue);
        }
    }

    public bool Enqueue(T item)
    {
        lock (queue)
        {
            if (closing || null == item)
            {
                return false;
            }

            queue.Enqueue(item);

            if (queue.Count == 1)
            {
                // wake up any blocked dequeue
                Monitor.PulseAll(queue);
            }

            return true;
        }
    }


    public void Close()
    {
        lock (queue)
        {
            if (!closing)
            {
                closing = true;
                queue.Clear();
                Monitor.PulseAll(queue);
            }
        }
    }


    public bool TryDequeue(out T value, int timeout = Timeout.Infinite)
    {
        lock (queue)
        {
            while (queue.Count == 0)
            {
                if (closing || (timeout < Timeout.Infinite) || !Monitor.Wait(queue, timeout))
                {
                    value = default(T);
                    return false;
                }
            }

            value = queue.Dequeue();
            return true;
        }
    }

    public void Clear()
    {
        lock (queue)
        {
            queue.Clear();
            Monitor.Pulse(queue);
        }
    }
}

Many thanks to Marc Gravell for this one!