Resource stack that waits if empty, until an element is pushed

Question

I want to build a stack of resources that will be used by different threads, but want to block to calling thread up to a timeout until a resource becomes available. The method WaitUntilTheStackHasMember() is the part I am lacking. I though of using a method like the one described on MSDN's timer and autoreset event, but it got complicated.

Is there an easier way to do this?

Class ResStack
{

    public TimeSpan TimeOut { get; set; }
    private object lockSync;
    private Stack<Resource> Resources;        

     ResStak()
     {
        // populate Stack
      }

    public void AddResource (Resource resource)
    {
        lock (lockSync)
        {
            Resource.Push(resource);
        }
    }

    private Resource PopRes()
    {
        Resource res = null;
        lock (lockSync)
        {
            if (Resources.Count > 0)
            {
                res = Resources.Pop();
            }
            else 
            {
                WaitUntilTheStackHasMember() // Not implemented
            }
        }
        return res;
    }

Answer 1

If you can use .NET 4, the BCL added a BlockingCollection<T> class that does exactly what you need. You can construct it with a ConcurrentStack<T> to achieve blocking stack semantics.

You'll want to use the TryTake(out T, TimeSpan) method for your timeout requirements.

Answer 2

Your method could repeatedly sleep and test until some time elapsed or a resource showed up. Have it return a flag indicating that it found a resource or timed out:

bool WaitUntilTheStackHasMember()
{
    TimeSpan waitPeriod = TimeSpan.FromSeconds(10);
    int sleepPeriod = 100; // milliseconds
    DateTime startTime = DateTime.Now;
    while ((Resources.Count == 0) && ((DateTime.Now - startTime) < waitPeriod))
    {
        System.Threading.Thread.Sleep(sleepPeriod);
    }
    return Resources.Count > 0;
}