* @since 10.0
 */
@GwtCompatible
@FunctionalInterface
@ElementTypesAreNonnullByDefault
public interface RemovalListener<K, V> {
  /**
   * Notifies the listener that a removal occurred at some point in the past.
   *
   * <p>This does not always signify that the key is now absent from the cache, as it may have
   * already been re-added.
   */
  // Technically should accept RemovalNotification<? extends K, ? extends V>, but because

   *
   * Past underutilization could mean that excess resources are available. Then, the RateLimiter
   * should speed up for a while, to take advantage of these resources. This is important when the
   * rate is applied to networking (limiting bandwidth), where past underutilization typically
   * translates to "almost empty buffers", which can be filled immediately.
   *

    return requireNonNull(DEST_TL.get());
  }

  /**
   * A thread-local destination buffer to keep us from creating new buffers. The starting size is
   * 1024 characters. If we grow past this we don't put it back in the threadlocal, we just keep
   * going and grow as needed.
   */
  private static final ThreadLocal<char[]> DEST_TL =
      new ThreadLocal<char[]>() {
        @Override

   *     arbitrary past or present time
   */
  abstract long queryEarliestAvailable(long nowMicros);

  /**
   * Reserves the requested number of permits and returns the time that those permits can be used
   * (with one caveat).
   *
   * @return the time that the permits may be used, or, if the permits may be used immediately, an
   *     arbitrary past or present time
   */

     *
     * The exception is the *InValueSet fields of multimapHeaderEntry, which are never set. (That
     * works out fine as long as we continue to be careful not to try to delete them or iterate
     * past them.)
     *
     * We could consider "lying" and omitting @CheckNotNull from all these fields. Normally, I'm not
     * a fan of that: What if we someday implement (presumably to be enabled during tests only)

     *
     * The exception is the *InValueSet fields of multimapHeaderEntry, which are never set. (That
     * works out fine as long as we continue to be careful not to try to delete them or iterate
     * past them.)
     *
     * We could consider "lying" and omitting @CheckNotNull from all these fields. Normally, I'm not
     * a fan of that: What if we someday implement (presumably to be enabled during tests only)

                // we dangerously assume E is a string
                List<E> extremeValues = (List<E>) getExtremeValues();
                @SuppressWarnings("unchecked")
                // map generators must past entry objects
                List<E> normalValues = (List<E>) Arrays.asList(entries);

                // prepare extreme values to be filtered out of view
                Collections.sort(extremeValues, comparator);

        if (lastFromForgetMeNot != null) {
          canRemove = true;
          return lastFromForgetMeNot;
        }
      }
      throw new NoSuchElementException("iterator moved past last element in queue.");
    }

    @Override
    public void remove() {
      checkRemove(canRemove);
      checkModCount();
      canRemove = false;
      expectedModCount++;

   *
   * <p>This is designed for generating persistent fingerprints of strings. It isn't
   * cryptographically secure, but it produces a high-quality hash with fewer collisions than some
   * alternatives we've used in the past.
   *
   * <p>FarmHash fingerprints are encoded by {@link HashCode#asBytes} in little-endian order. This
   * means {@link HashCode#asLong} is guaranteed to return the same value that

   * checkNotNull *should* be annotated to require it to be non-null.
   *
   * However, for a variety of reasons, Google developers have written a ton of code over the past
   * decade that assumes that they can use checkNotNull for non-precondition checks. I had hoped to
   * take a principled stand on this, but the amount of such code is simply overwhelming. To avoid