public abstract class WorkerBase<S, I, O> {
  public WorkerBase() { }

  public virtual bool Initialize() {
    return true;
  }

  public abstract List<O> Process(S settings, List<I> input);
}

static ObjectPool<MyPool, MyPool.Settings, MyPool.Input, MyPool.Output> myPool = new ObjectPool<MyPool, MyPool.Settings, MyPool.Input, MyPool.Output>();

// Later...
var output = myPool.Process(settings, input);

public class ObjectPool<T, S, I, O> where T : WorkerBase<S, I, O>, new() {
  /* Much implementation omitted for sake of clarity */

  public List<O> Process(S settings, List<I> input) {
    // Indirectly calls worker's Process function
  }
}