package locklib.sx;
   
   import locklib.LockPolicy;
   import ensure.Ensure;
   
   /**
    * Locking policy for SX locking. In an SX locking policy, locking a
    * child requires share-locking its parent.
    */
  public class SxLockPolicy implements LockPolicy<SxLockType> {
  	/**
  	 * Is starvation allowed?
  	 */
  	private boolean m_starvation_allowed;
  	
  	/**
  	 * Creates a new SX locking policy.
  	 * @param starvation_allowed is starvation allowed? (see
  	 * {@link LockPolicy#starvation_allowed()})
  	 */
  	public SxLockPolicy(boolean starvation_allowed) {
  		m_starvation_allowed = starvation_allowed;
  	}
  
  	@Override
  	public boolean is_compatible(SxLockType lock_type_1,
  			SxLockType lock_type_2) {
  		Ensure.not_null(lock_type_1, "lock_type_1 == null");
  		Ensure.not_null(lock_type_2, "lock_type_2 == null");
  		
  		if (lock_type_1 == SxLockType.S_LOCK
  				&& lock_type_2 == SxLockType.S_LOCK) {
  			return true;
  		}
  		
  		return false;
  	}
  
  	@Override
  	public SxLockType parent_lock(SxLockType lock_type) {
  		Ensure.not_null(lock_type, "lock_type == null");
  		
  		return SxLockType.S_LOCK;
  	}
  	
  	@Override
  	public boolean starvation_allowed() {
  		return m_starvation_allowed;
  	}
  }