* 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();

@RunWith(JUnit4.class)
@NullUnmarked
public class FinalizableReferenceQueueTest {

  private @Nullable FinalizableReferenceQueue frq;

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

  @Test
  public void testFinalizeReferentCalled() {
    MockReference reference = new MockReference(frq = new FinalizableReferenceQueue());

    GcFinalization.awaitDone(() -> reference.finalizeReferentCalled);
  }

  /*
   * 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

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

import com.google.common.annotations.J2ktIncompatible;
import com.google.errorprone.annotations.DoNotMock;

/**
 * Implemented by references that have code to run after garbage collection of their referents.
 *
 * @see FinalizableReferenceQueue
 * @author Bob Lee
 * @since 2.0
 */
@DoNotMock("Use an instance of one of the Finalizable*Reference classes")
@J2ktIncompatible
@GwtIncompatible
public interface FinalizableReference {
  /**

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