[2008.07.10] Coordinate Data Structures in System.Threading.Collections [Part I/II]

• the IConcurrentCollection<T> interface represents a collection which in a thread safe way you can add or remove from
• some implementations of this are:
  • ConcurrentStack<T>
  • ConcurrentQueue<T>

[1] System.Threading.Collections.ConcurrentQueue<T>

• NOTE: I will drop the System namespace below to avoid overflow but it precedes all the namespaces listed
• Threading.Collections.ConcurrentQueue<T> is a thread-safe and scalable queue data structure
• as with its Collections.Generics.Queue<T> counterpart, ConcurrentQueue<T> provides an Enqueue method for adding an element to the queue
• unlike Queue<T>, however, ConcurrentQueue<T> does not provide a Dequeue method for removing an item from the queue
• instead, it provides a TryDequeue method that returns a Boolean value indicating whether an item could be dequeued and an out parameter containing the dequeued element if one could be retrieved
• while Queue<T> provides Enqueue/Dequeue methods, ConcurrentQueue<T> provides the Enqueue/TryDequeue methods

Example: consider a loop meant to remove each element from the queue and process it

Using Queue<T>

while (queue.Count > 0) {     Data d = stack.Dequeue();     Process(d); }

Using ConcurrentQueue<T>

Data d; while (queue.TryDequeue(out d)) {     Process(d); }

[2] System.Threading.Collections.ConcurrentStack<T>

• ConcurrentStack<T> serves as a thread-safe alternative to Collections.Generics.Stack<T>
• while Stack<T> provides Push/Pop methods, ConcurrentStack<T> provides the Push/TryPop methods

Example:

Using Stack<T>

Stack<T> stack = new Stack<T>(); while (stack.Count > 0) {     Use(stack.Pop()); } // in this stack implmentation one would // have had to lock around the axis // of both stack.Count and stack.Pop

Using ConcurrentStack<T>

ConcurrentStack<T> cStack = new ConcurrentStack<T>(); T data; while (cStack.Count > 0) {     Use(cStack.TryPop()); } // TryPop says try and get something and //  if its available give it to me