* number of well-known problems. Here is how you might use this class instead:
 *
 * <pre>{@code
 * 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();

/**
 * Unit test for {@link FinalizableReferenceQueue}.
 *
 * @author Bob Lee
 */
// - depends on details of GC and classloading
// - .class files aren't available
// - possibly no real concept of separate ClassLoaders?
@AndroidIncompatible
@GwtIncompatible
public class FinalizableReferenceQueueTest extends TestCase {

  private @Nullable FinalizableReferenceQueue frq;

  @Override

  /*
   * 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

-keep class sun.misc.JavaLangAccess {
  *** getStackTraceElement(...);
  *** getStackTraceDepth(...);
}

# FinalizableReferenceQueue calls this reflectively
# Proguard is intelligent enough to spot the use of reflection onto this, so we
# only need to keep the names, and allow it to be stripped out if
# FinalizableReferenceQueue is unused.
-keepnames class com.google.common.base.internal.Finalizer {
  *** startFinalizer(...);
}

   * Constructs a new finalizable soft reference.
   *
   * @param referent to softly reference
   * @param queue that should finalize the referent
   */
  protected FinalizableSoftReference(@CheckForNull T referent, FinalizableReferenceQueue queue) {
    super(referent, queue.queue);
    queue.cleanUp();
  }

   *
   * @param referent to phantom reference
   * @param queue that should finalize the referent
   */
  protected FinalizablePhantomReference(@CheckForNull T referent, FinalizableReferenceQueue queue) {
    super(referent, queue.queue);
    queue.cleanUp();
  }

   * Constructs a new finalizable weak reference.
   *
   * @param referent to weakly reference
   * @param queue that should finalize the referent
   */
  protected FinalizableWeakReference(@CheckForNull T referent, FinalizableReferenceQueue queue) {
    super(referent, queue.queue);
    queue.cleanUp();
  }

   * Constructs a new finalizable weak reference.
   *
   * @param referent to weakly reference
   * @param queue that should finalize the referent
   */
  protected FinalizableWeakReference(@CheckForNull T referent, FinalizableReferenceQueue queue) {
    super(referent, queue.queue);
    queue.cleanUp();
  }