How can I implement a reusable object pool in C#?

imho it's a valid question. Especially when working with socket servers where allocating buffers is done frequently. It's called flyweight pattern.

But I wouldn't take the decision to use it lightly.

class BufferPool<T>
{
    private readonly Func<T> _factoryMethod;
    private ConcurrentQueue<T> _queue = new ConcurrentQueue<T>();

    public BufferPool(Func<T> factoryMethod)
    {
        _factoryMethod = factoryMethod;
    }

    public void Allocate(int count)
    {
        for (int i = 0; i < count; i++)
            _queue.Enqueue(_factoryMethod());
    }

    public T Dequeue()
    {
        T buffer;
        return !_queue.TryDequeue(out buffer) ? _factoryMethod() : buffer;
    }

    public void Enqueue(T buffer)
    {
        _queue.Enqueue(buffer);
    }
}

Usage:

var myPool = new BufferPool<byte[]>(() => new byte[65535]);
myPool.Allocate(1000);

var buffer= myPool.Dequeue();
// .. do something here ..
myPool.Enqueue(buffer);