package locklib;
   
   import java.util.Collections;
   import java.util.HashSet;
   import java.util.Iterator;
   import java.util.LinkedList;
   import java.util.Set;
   
   import ensure.Ensure;
  
  /**
   * Wait queue that keeps requests in a FIFO queue.
   * @param <LockType> the type of locks
   */
  public class FifoWaitQueue<LockType> extends WaitQueue<LockType> {
  	/**
  	 * Queued requests.
  	 */
  	private LinkedList<LockGrantFuture<LockType>> m_queue;
  	
  	/**
  	 * Set with all lock requests in the queue.
  	 */
  	private Set<LockGrantFuture<LockType>> m_set;
  	
  	/**
  	 * Creates a new wait queue.
  	 */
  	public FifoWaitQueue() {
  		m_queue = new LinkedList<>();
  		m_set = new HashSet<>();
  	}
  	
  	@Override
  	public Iterator<LockGrantFuture<LockType>> iterator() {
  		return Collections.unmodifiableList(m_queue).iterator();
  	}
  
  	@Override
  	protected void enqueue(LockGrantFuture<LockType> r) {
  		Ensure.not_null(r, "r != null");
  		Ensure.is_false(m_set.contains(r), "m_set.contains(r)");
  		m_queue.addLast(r);
  		m_set.add(r);
  	}
  
  	@Override
  	protected void dequeue(LockGrantFuture<LockType> r) {
  		Ensure.not_null(r, "r == null");
  		m_queue.remove(r);
  		m_set.remove(r);
  	}
  }