Question

What would be the correct usage of either, BlockingCollection or ConcurrentQueue so you can freely dequeue items without burning out half or more of your CPU using a thread ?

I was running some tests using 2 threads and unless I had a Thread.Sleep of at least 50~100ms it would always hit at least 50% of my CPU.

Here is a fictional example:

private void _DequeueItem()
{
    object o = null;
    while(socket.Connected)
    {
        while (!listOfQueueItems.IsEmpty)
        {
            if (listOfQueueItems.TryDequeue(out o))
            {
                // use the data
            }
        }
    }
}

With the above example I would have to set a thread.sleep so the cpu doesnt blow up.

Note: I have also tried it without the while for IsEmpty check, result was the same.

Answer 1

It is not because of the BlockingCollection or ConcurrentQueue, but the while loop:

while(socket.Connected)
{
    while (!listOfQueueItems.IsEmpty)
    { /*code*/ }
}

Of course it will take the cpu down; because of if the queue is empty, then the while loop is just like:

while (true) ;

which in turn will eat the cpu resources.

This is not a good way of using ConcurrentQueue you should use AutoResetEvent with it so whenever item is added you will be notified.
Example:

private ConcurrentQueue<Data> _queue = new ConcurrentQueue<Data>();
private AutoResetEvent _queueNotifier = new AutoResetEvent(false);

//at the producer:
_queue.Enqueue(new Data());
_queueNotifier.Set();

//at the consumer:
while (true)//or some condition
{
    _queueNotifier.WaitOne();//here we will block until receive signal notification.
    Data data;
    if (_queue.TryDequeue(out data))
    {
        //handle the data
    }
}

For a good usage of the BlockingCollection you should use the GetConsumingEnumerable() to wait for the items to be added, Like:

//declare the buffer
private BlockingCollection<Data> _buffer = new BlockingCollection<Data>(new ConcurrentQueue<Data>());

//at the producer method:
_messageBuffer.Add(new Data());

//at the consumer
foreach (Data data in _buffer.GetConsumingEnumerable())//it will block here automatically waiting from new items to be added and it will not take cpu down 
{
    //handle the data here.
}