offer(e); // never need to block
  }

  @CanIgnoreReturnValue // pushed down from class to method
  @Override
  public @Nullable E poll() {
    final Monitor monitor = this.monitor;
    monitor.enter();
    try {
      return q.poll();
    } finally {
      monitor.leave();
    }
  }

  @CanIgnoreReturnValue // pushed down from class to method
  @Override

@GwtCompatible(emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
@ElementTypesAreNonnullByDefault
// TODO(kevinb): I think we should push everything down to "BaseImmutableCollection" or something,
// just to do everything we can to emphasize the "practically an interface" nature of this class.

  }

  private void assertNoExpectedFailures() {
    assertWithMessage("executor was shut down")
        .that(shutdownAndAwaitTermination(executor, 10, SECONDS))
        .isTrue();
    assertWithMessage("closingExecutor was shut down")
        .that(shutdownAndAwaitTermination(closingExecutor, 10, SECONDS))
        .isTrue();
    if (!failures.isEmpty()) {

      result.descendingSet = this;
    }
    return result;
  }

  // Most classes should implement this as new DescendingImmutableSortedSet<E>(this),
  // but we push down that implementation because ProGuard can't eliminate it even when it's always
  // overridden.
  @GwtIncompatible // NavigableSet
  abstract ImmutableSortedSet<E> createDescendingSet();

  /** @since 12.0 */

    return isRunning ? ticker.read() - startTick + elapsedNanos : elapsedNanos;
  }

  /**
   * Returns the current elapsed time shown on this stopwatch, expressed in the desired time unit,
   * with any fraction rounded down.
   *
   * <p>Note that the overhead of measurement can be more than a microsecond, so it is generally not
   * useful to specify {@link TimeUnit#NANOSECONDS} precision here.
   *

   * NavigableSets inherit the tests for filtered Iterables, Collections, Sets, and SortedSets. The
   * actual implementation tests are further down.
   */

  public abstract static class AbstractFilteredIterableTest<C extends Iterable<Integer>>
      extends TestCase {
    abstract C createUnfiltered(Iterable<Integer> contents);

   * }</pre>
   */
  private static final SuccessorsFunction<Character> JAVADOC_GRAPH =
      createUndirectedGraph("ba", "ad", "be", "ac", "ec", "cf");

  /**
   * A diamond shaped directed graph (arrows going down):
   *
   * <pre>{@code
   *   a
   *  / \
   * b   c
   *  \ /
   *   d
   * }</pre>
   */
  private static final SuccessorsFunction<Character> DIAMOND_GRAPH =

    }

    final Iterator<N> preOrder(Iterator<? extends N> startNodes) {
      return topDown(startNodes, InsertionOrder.FRONT);
    }

    /**
     * In top-down traversal, an ancestor node is always traversed before any of its descendant
     * nodes. The traversal order among descendant nodes (particularly aunts and nieces) are

  }

  private void assertNoExpectedFailures() {
    assertWithMessage("executor was shut down")
        .that(shutdownAndAwaitTermination(executor, 10, SECONDS))
        .isTrue();
    assertWithMessage("closingExecutor was shut down")
        .that(shutdownAndAwaitTermination(closingExecutor, 10, SECONDS))
        .isTrue();
    if (!failures.isEmpty()) {

      }
      copy(resourceUrl, file);
    }

    return file;
  }

  /**
   * Creates a new temp dir for testing. The returned directory and all contents of it will be
   * deleted in the tear-down for this test.
   */
  protected final File createTempDir() throws IOException {
    File tempFile = File.createTempFile("IoTestCase", "");
    if (!tempFile.delete() || !tempFile.mkdir()) {