Enqueued event for Queue in C#

Question

I am new to event and delegates. How can I implement an enqueued event for an object of type Queue?

I am using C# and .Net 4.0

Answer 1

There are no events fired from the System.Collections.* suite of classes. Since you're using .NET 4.0, you may want to look into BlockingCollection<T> instead which, instead of relying on events, you would use the Producer-Consumer pattern to Take elements from the collection as they arrive from another thread. BlockingCollection<T> will take care of all thread-safety and synchronization for you efficiently.

The default backing type for BlockingCollection<T> is ConcurrentQueue<T> which sounds like what you want, but it should be noted that you can change it to use a ConcurrentStack<T> or ConcurrentBag<T> if you want/don't mind different ordering characteristics.

Another great feature of BlockingCollection<T> is the ability to set bounds which can help block the producer from adding more items to the collection than the consumers can keep up with.

For a great write up on all aspects of this subject, I suggest checking out this blog post from Alexeandra Rusina. The post also covers ways to work with BlockingCollection using the Task Parallel Library.

Answer 2

You can encapsulate the Queue class with your own class, something like:

class MyQueue<T>
{
    private readonly Queue<T> queue = new Queue<T>();     
    public event EventHandler Enqueued;     
    protected virtual void OnEnqueued()     
    {         
        if (Enqueued != null) 
        Enqueued(this, EventArgs e);     
    }     
    public virtual void Enqueue(T item)     
    {         
        queue.Enqueue(item);         
        OnEnqueued();     
    }     
    public int Count 
     {
             get 
             { 
                     return queue.Count; 
             }
     }
    public virtual T Dequeue()     
    {
            T item = queue.Dequeue();         
            OnEnqueued();
            return item;
        }
}