* </ul>
 *
 * <p>Invalid:
 *
 * <ul>
 *   <li>Expired: time expired (key/value may still be set)
 *   <li>Collected: key/value was partially collected, but not yet cleaned up
 *   <li>Unset: marked as unset, awaiting cleanup or reuse
 * </ul>
 */
@GwtIncompatible
@ElementTypesAreNonnullByDefault
interface ReferenceEntry<K, V> {
  /** Returns the value reference from this entry. */
  @CheckForNull

   *
   * <p>The {@code shutdownNow} method of the returned executor always returns an empty list despite
   * the fact that everything is still technically awaiting execution. The {@code getDelay} method
   * of any {@link ScheduledFuture} returned by the executor will always return the max long value
   * instead of the time until the user-specified delay.
   */

    }

    val isRunning = promoteAndExecute()

    if (!isRunning && idleCallback != null) {
      idleCallback.run()
    }
  }

  /** Returns a snapshot of the calls currently awaiting execution. */
  fun queuedCalls(): List<Call> =
    this.withLock {
      return Collections.unmodifiableList(readyAsyncCalls.map { it.call })
    }

   *
   * <p>Among the improvements that this method and {@code LoadingCache.get(K)} both provide are:
   *
   * <ul>
   *   <li>{@linkplain LoadingCache#get(Object) awaiting the result of a pending load} rather than
   *       starting a redundant one
   *   <li>eliminating the error-prone caching boilerplate
   *   <li>tracking load {@linkplain #stats statistics}
   * </ul>
   *

   *
   * <p>Among the improvements that this method and {@code LoadingCache.get(K)} both provide are:
   *
   * <ul>
   *   <li>{@linkplain LoadingCache#get(Object) awaiting the result of a pending load} rather than
   *       starting a redundant one
   *   <li>eliminating the error-prone caching boilerplate
   *   <li>tracking load {@linkplain #stats statistics}
   * </ul>
   *