checkNotNull(valuesFunction);
    return collectingAndThen(
        flatteningToMultimap(
            input -> checkNotNull(keyFunction.apply(input)),
            input -> valuesFunction.apply(input).peek(Preconditions::checkNotNull),
            MultimapBuilder.linkedHashKeys().arrayListValues()::<K, V>build),
        ImmutableListMultimap::copyOf);
  }

  static <T extends @Nullable Object, K, V>

 *     .maximumSize(1000)
 *     .create();
 * }</pre>
 *
 * <p>As a {@link Queue} it functions exactly as a {@link PriorityQueue}: its head element -- the
 * implicit target of the methods {@link #peek()}, {@link #poll()} and {@link #remove()} -- is
 * defined as the <i>least</i> element in the queue according to the queue's comparator. But unlike
 * a regular priority queue, the methods {@link #peekLast}, {@link #pollLast} and {@link

  }

  /** Checks that #drain() invocations behave correctly for a drained (empty) queue. */
  private void assertDrained(BlockingQueue<Object> q) {
    assertNull(q.peek());
    assertInterruptibleDrained(q);
    assertUninterruptibleDrained(q);
  }

  private void assertInterruptibleDrained(BlockingQueue<Object> q) {
    // nothing to drain, thus this should wait doing nothing

        "Should be able to peek() middle element multiple times", "B", peekingIterator.peek());
    assertEquals(
        "next() should still return middle element after peeking", "B", peekingIterator.next());

    assertEquals("Should be able to peek() at last element", "C", peekingIterator.peek());
    assertEquals(
        "Should be able to peek() last element multiple times", "C", peekingIterator.peek());
    assertEquals(

                    } catch (ExecutionException expected) {
                    }
                    try {
                      peeker.getDone(nonInput);
                      fail("Peeker should not be able to peek into non-input ClosingFuture.");
                    } catch (IllegalArgumentException expected) {
                    }
                    capturedPeeker.set(peeker);
                    return closeable2;

    Iterator<Integer> consumingIterator = Iterables.consumingIterable(queue).iterator();

    assertEquals(5, queue.peek().intValue());
    assertEquals(5, consumingIterator.next().intValue());

    assertEquals(14, queue.peek().intValue());
    assertTrue(consumingIterator.hasNext());
    assertTrue(queue.isEmpty());
  }

  public void testConsumingIterable_noIteratorCall() {

  }

  @CanIgnoreReturnValue
  @Override
  @ParametricNullness
  public E remove() {
    return delegate().remove();
  }

  @Override
  @CheckForNull
  public E peek() {
    return delegate().peek();
  }

  @Override
  @ParametricNullness
  public E element() {
    return delegate().element();
  }

  /**

    public boolean remove(Object object) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.remove(object);
    }

    @Override
    public @Nullable E peek() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peek();
    }

    @Override
    public E element() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.element();
    }

    @Override

   * contract of {@link PeekingIterator#peek()}.
   *
   * <p>Implementations of {@code AbstractIterator} that wish to expose this functionality should
   * implement {@code PeekingIterator}.
   */
  @ParametricNullness
  public final T peek() {
    if (!hasNext()) {
      throw new NoSuchElementException();
    }

                  .iterator());
      Cut<C> cut;
      if (positiveItr.hasNext()) {
        cut =
            (positiveItr.peek().upperBound == Cut.<C>aboveAll())
                ? positiveItr.next().lowerBound
                : positiveRangesByLowerBound.higherKey(positiveItr.peek().upperBound);
      } else if (!complementLowerBoundWindow.contains(Cut.<C>belowAll())