import java.util.*;

public class SetLock implements LockInvokable {
   private Set s;
   public SetLock(Set s) { this.s = s; }

   public void lockInvoke(Runnable r) {
      helper(s.iterator(), r);
   }

   private void helper(Iterator i, Runnable r) {
       if (i.hasNext()) {
         synchronized(i.next()) {
            helper(i, r);
         }
       } 
       else r.run();
    }
}