package jutil;

/**
 * The methods in this class are meant to mimic the
 * indivisible swap and testAndSet instructions
 * provided by most computers.
 */
public class Lock {
	/**
	 * if true, then lock is locked
	 */
   private boolean locked = false;
   /**
    * @param  val  initial value of lock
    */
   public Lock(boolean val) { locked = val; }
   /**
    * sets lock to false
    */
   public Lock() { this(false); }
   /**
    * @return state of lock
    */
   public synchronized boolean isLocked() { return locked; }
   /**
    * sets lock to true without interruption.
    */
   public synchronized void lock() { locked = true; }
   /**
    * Sets lock to false without interruption.
    */
   public synchronized void unlock() { locked = false; }
   /**
    * sets lock to true without interruption
    * @return former value of lock
    */
   public synchronized boolean testAndSet() {
	   boolean temp = locked;
	   locked = true;
	   return temp;
   }
   /**
    * Swaps this locks state with the state of another
    * lock without interruption.
    * @param other  some other lock
    */
   public synchronized void swap(Lock other) {
	   boolean temp = locked;
	   locked = other.locked;
	   other.locked = temp;
   }
}