How Can I Implement a Fixed-Size Queue with Automatic Dequeueing in C#?

Creating a C# Fixed-Size Queue with Automatic Dequeueing

Many applications need a data structure that holds a fixed number of items, removing the oldest when it's full. This is useful for tracking recent events or maintaining a history. Imagine a web browser needing to store the last 100 URLs visited. While ConcurrentQueue<T> could work, managing the dequeuing manually is inefficient. A custom wrapper class provides a cleaner solution.

The FixedSizedQueue<T> Class

This class wraps a ConcurrentQueue<T>, handling both enqueueing and dequeueing to maintain a set size. The class definition includes:

<code class="language-csharp">public class FixedSizedQueue<T>
{
    private readonly ConcurrentQueue<T> queue = new ConcurrentQueue<T>();
    private readonly object lockObject = new object();
    public int Limit { get; set; }
    // ... other methods
}</code>

The Enqueue Method

The Enqueue method adds items. If the queue exceeds the limit, it removes older items:

<code class="language-csharp">public void Enqueue(T item)
{
    queue.Enqueue(item);
    lock (lockObject)
    {
        T overflow;
        while (queue.Count > Limit && queue.TryDequeue(out overflow)) ;
    }
}</code>

Using FixedSizedQueue<T>

To use the class, create an instance and set the limit:

<code class="language-csharp">var urlHistory = new FixedSizedQueue<string> { Limit = 100 };</code>

Adding items automatically maintains the size:

<code class="language-csharp">urlHistory.Enqueue("www.google.com");  // Enqueues the URL
urlHistory.Enqueue("www.microsoft.com"); // The oldest URL is automatically dequeued</code>

This approach provides a more elegant and efficient way to manage fixed-size queues in C#.

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