Striped<ReadWriteLock> striped = Striped.lazyWeakReadWriteLock(1000);
    Object key = new Object();
    Lock readLock = striped.get(key).readLock();
    WeakReference<Object> garbage = new WeakReference<>(new Object());
    GcFinalization.awaitClear(garbage);
    Lock writeLock = striped.get(key).writeLock();
    readLock.lock();
    assertFalse(writeLock.tryLock());
    readLock.unlock();
  }

import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A notification of the removal of a single entry. The key and/or value may be null if they were
 * already garbage collected.
 *
 * <p>Like other {@code Entry} instances associated with {@code CacheBuilder}, this class holds
 * strong references to the key and value, regardless of the type of references the cache may be
 * using.
 *

    Striped<ReadWriteLock> striped = Striped.lazyWeakReadWriteLock(1000);
    Object key = new Object();
    Lock readLock = striped.get(key).readLock();
    WeakReference<Object> garbage = new WeakReference<>(new Object());
    GcFinalization.awaitClear(garbage);
    Lock writeLock = striped.get(key).writeLock();
    readLock.lock();
    assertFalse(writeLock.tryLock());
    readLock.unlock();
  }

    return new InternerBuilder();
  }

  /**
   * Returns a new thread-safe interner which retains a strong reference to each instance it has
   * interned, thus preventing these instances from being garbage-collected. If this retention is
   * acceptable, this implementation may perform better than {@link #newWeakInterner}.
   */
  public static <E> Interner<E> newStrongInterner() {
    return newBuilder().strong().build();

import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import javax.annotation.CheckForNull;

/**
 * Phantom reference with a {@code finalizeReferent()} method which a background thread invokes
 * after the garbage collector reclaims the referent. This is a simpler alternative to using a
 * {@link ReferenceQueue}.
 *
 * <p>Unlike a normal phantom reference, this reference will be cleared automatically.
 *
 * @author Bob Lee

   * and {@code intern(a) == intern(b)} if and only if {@code a.equals(b)}. Note that {@code
   * intern(a)} is permitted to return one instance now and a different instance later if the
   * original interned instance was garbage-collected.
   *
   * <p><b>Warning:</b> do not use with mutable objects.
   *
   * @throws NullPointerException if {@code sample} is null
   */
  E intern(E sample);

import com.google.common.annotations.GwtIncompatible;
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

import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import javax.annotation.CheckForNull;

/**
 * Soft reference with a {@code finalizeReferent()} method which a background thread invokes after
 * the garbage collector reclaims the referent. This is a simpler alternative to using a {@link
 * ReferenceQueue}.
 *
 * @author Bob Lee
 * @since 2.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault

 * loader. That way, this class doesn't prevent the main class loader from getting garbage
 * collected, and this class can detect when the main class loader has been garbage collected and
 * stop itself.
 */
// no @ElementTypesAreNonNullByDefault for the reasons discussed above
public class Finalizer implements Runnable {

  private static final Logger logger = Logger.getLogger(Finalizer.class.getName());

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import javax.annotation.CheckForNull;

/**
 * Weak reference with a {@code finalizeReferent()} method which a background thread invokes after
 * the garbage collector reclaims the referent. This is a simpler alternative to using a {@link
 * ReferenceQueue}.
 *
 * @author Bob Lee
 * @since 2.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault