@SuppressWarnings("unchecked") // implementation is "fully variant"
    SupplierFunction<T> sf = (SupplierFunction<T>) SupplierFunctionImpl.INSTANCE;
    return sf;
  }

  private interface SupplierFunction<T extends @Nullable Object> extends Function<Supplier<T>, T> {}

  private enum SupplierFunctionImpl implements SupplierFunction<@Nullable Object> {
    INSTANCE;

   * the discussion in the {@link #addListener} documentation. All its warnings about heavyweight
   * listeners are also applicable to heavyweight callbacks passed to this method.
   *
   * <p>For a more general interface to attach a completion listener, see {@link #addListener}.
   *
   * <p>This method is similar to {@link java.util.concurrent.CompletableFuture#whenComplete} and

  private static List<Object> subListCopy(Object[] source, int size) {
    final Object[] copy = new Object[size];
    System.arraycopy(source, 0, copy, 0, size);
    return Arrays.asList(copy);
  }

  private interface IteratorOperation {
    @Nullable Object execute(Iterator<?> iterator);
  }

  /**
   * Apply this method to both iterators and return normally only if both produce the same response.
   *

  public static class SimpleThreadFactory implements ThreadFactory {
    @Override
    public Thread newThread(Runnable r) {
      return new Thread(r);
    }
  }

  public interface TrackedRunnable extends Runnable {
    boolean isDone();
  }

  public static TrackedRunnable trackedRunnable(final long timeoutMillis) {
    return new TrackedRunnable() {

    implements Serializable {

  /**
   * Creates a new, empty multiset, sorted according to the elements' natural order. All elements
   * inserted into the multiset must implement the {@code Comparable} interface. Furthermore, all
   * such elements must be <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
   * {@code ClassCastException} for any elements {@code e1} and {@code e2} in the multiset. If the

  //
  // This idea has come up from time to time, and I think one of my
  // earlier versions of Monitor even did something like this. I ended
  // up strongly favoring the current interface.
  //
  // I probably can't remember all the reasons (it's possible you
  // could find them in the code review archives), but here are a few:
  //
  // 1. What about leaving/unlocking? Are you going to do

 * (doing so results in {@code ClassCastException}).
 *
 * <p>This class and its iterator implement all of the optional methods of the {@link
 * Collection} and {@link Iterator} interfaces. The Iterator provided in method {@link #iterator()}
 * is not guaranteed to traverse the elements of the MonitorBasedPriorityBlockingQueue in
 * any particular order. If you need ordered traversal, consider using {@code

import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * An interface for <a
 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data,
 * whose edges are unique objects.
 *
 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
 *
 * <p>There are three primary interfaces provided to represent graphs. In order of increasing

 * loading), and fewer <a
 * href="https://github.com/google/guava/issues?q=is%3Aopen+is%3Aissue+label%3Apackage%3Dcache+label%3Atype%3Ddefect">bugs</a>.
 *
 * <p>Caffeine defines its own interfaces (<a
 * href="https://www.javadoc.io/doc/com.github.ben-manes.caffeine/caffeine/latest/com.github.benmanes.caffeine/com/github/benmanes/caffeine/cache/Cache.html">{@code
 * Cache}</a>, <a

 * but reduces variability and avoids starvation.
 *
 * <p>This class and its iterator implement all of the optional methods of the {@link
 * Collection} and {@link Iterator} interfaces.
 *
 * @author Doug Lea
 * @author Justin T. Sampson
 * @param <E> the type of elements held in this collection
 */
// TODO(kak): consider removing some of the @CanIgnoreReturnValue annotations as appropriate