* number of well-known problems. Here is how you might use this class instead:
 *
 * {@snippet :
 * public class MyServer implements Closeable {
 *   private static final FinalizableReferenceQueue frq = new FinalizableReferenceQueue();
 *   // You might also share this between several objects.
 *
 *   private static final Set<Reference<?>> references = Sets.newConcurrentHashSet();

 * number of well-known problems. Here is how you might use this class instead:
 *
 * {@snippet :
 * public class MyServer implements Closeable {
 *   private static final FinalizableReferenceQueue frq = new FinalizableReferenceQueue();
 *   // You might also share this between several objects.
 *
 *   private static final Set<Reference<?>> references = Sets.newConcurrentHashSet();

  /*
   * The following tests check that the use of FinalizableReferenceQueue does not prevent the
   * ClassLoader that loaded that class from later being garbage-collected. If anything continues
   * to reference the FinalizableReferenceQueue class then its ClassLoader cannot be
   * garbage-collected, even if there are no more instances of FinalizableReferenceQueue itself.
   * The code in FinalizableReferenceQueue goes to considerable trouble to ensure that there are

import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/**
 * Unit test for {@link FinalizableReferenceQueue}.
 *
 * @author Bob Lee
 */
@J2ktIncompatible
@GwtIncompatible
@RunWith(JUnit4.class)
@NullUnmarked
public class FinalizableReferenceQueueTest {

  private @Nullable FinalizableReferenceQueue frq;

  @After
  public void tearDown() throws Exception {
    frq = null;
  }

  @Test

  /*
   * The following tests check that the use of FinalizableReferenceQueue does not prevent the
   * ClassLoader that loaded that class from later being garbage-collected. If anything continues
   * to reference the FinalizableReferenceQueue class then its ClassLoader cannot be
   * garbage-collected, even if there are no more instances of FinalizableReferenceQueue itself.
   * The code in FinalizableReferenceQueue goes to considerable trouble to ensure that there are

  /**
   * Starts the Finalizer thread. FinalizableReferenceQueue calls this method reflectively.
   *
   * @param finalizableReferenceClass FinalizableReference.class.
   * @param queue a reference queue that the thread will poll.
   * @param frqReference a phantom reference to the FinalizableReferenceQueue, which will be queued
   *     either when the FinalizableReferenceQueue is no longer referenced anywhere, or when its

  /**
   * Starts the Finalizer thread. FinalizableReferenceQueue calls this method reflectively.
   *
   * @param finalizableReferenceClass FinalizableReference.class.
   * @param queue a reference queue that the thread will poll.
   * @param frqReference a phantom reference to the FinalizableReferenceQueue, which will be queued
   *     either when the FinalizableReferenceQueue is no longer referenced anywhere, or when its

    return new WeakReference<>(referent);
  }

  private static final class FinalizableReference extends FinalizablePhantomReference<Object> {
    static final FinalizableReferenceQueue referenceQueue = new FinalizableReferenceQueue();
    static final Set<FinalizableReference> references = newConcurrentHashSet();

    static void register(Object referent, CountDownLatch latch) {

    return new WeakReference<>(referent);
  }

  private static final class FinalizableReference extends FinalizablePhantomReference<Object> {
    static final FinalizableReferenceQueue referenceQueue = new FinalizableReferenceQueue();
    static final Set<FinalizableReference> references = newConcurrentHashSet();

    static void register(Object referent, CountDownLatch latch) {

      FinalizableReference.register(byteSource);
    }
  }

  private static final class FinalizableReference extends FinalizablePhantomReference<ByteSource> {
    static final FinalizableReferenceQueue referenceQueue = new FinalizableReferenceQueue();
    static final Set<FinalizableReference> references = newConcurrentHashSet();

    static void register(FbosByteSource referent) {