*/
@J2ktIncompatible
@GwtIncompatible
public abstract class FinalizablePhantomReference<T> extends PhantomReference<T>
    implements FinalizableReference {
  /**
   * Constructs a new finalizable phantom reference.
   *
   * @param referent to phantom reference
   * @param queue that should finalize the referent
   */
  protected FinalizablePhantomReference(@Nullable T referent, FinalizableReferenceQueue queue) {

 *   // You might also share this between several objects.
 *
 *   private static final Set<Reference<?>> references = Sets.newConcurrentHashSet();
 *   // This ensures that the FinalizablePhantomReference itself is not garbage-collected.
 *
 *   private final ServerSocket serverSocket;
 *
 *   private MyServer(...) {
 *     ...
 *     this.serverSocket = new ServerSocket(...);
 *     ...
 *   }
 *

      MyServerExampleWithFrq myServer = new MyServerExampleWithFrq();
      ServerSocket serverSocket = myServer.serverSocket;
      Reference<?> reference =
          new FinalizablePhantomReference<MyServerExampleWithFrq>(myServer, frq) {
            @Override
            public void finalizeReferent() {
              references.remove(this);
              if (!serverSocket.isClosed()) {