// TODO: verify contents afterward
    // TODO: something shiny and new instead of Stack
    // TODO: test whether null is supported (create a Feature)
    /**
     * The elements to be returned by future calls to {@code next()}, with the first at the top of
     * the stack.
     */
    final Stack<E> nextElements = new Stack<>();

    /**

    }
  }

  /**
   * Returns a string containing the result of {@link Throwable#toString() toString()}, followed by
   * the full, recursive stack trace of {@code throwable}. Note that you probably should not be
   * parsing the resulting string; if you need programmatic access to the stack frames, you can call
   * {@link Throwable#getStackTrace()}.
   */
  @GwtIncompatible // java.io.PrintWriter, java.io.StringWriter

    }
  }

  /**
   * Returns a string containing the result of {@link Throwable#toString() toString()}, followed by
   * the full, recursive stack trace of {@code throwable}. Note that you probably should not be
   * parsing the resulting string; if you need programmatic access to the stack frames, you can call
   * {@link Throwable#getStackTrace()}.
   */
  @GwtIncompatible // java.io.PrintWriter, java.io.StringWriter

    // TODO: verify contents afterward
    // TODO: something shiny and new instead of Stack
    // TODO: test whether null is supported (create a Feature)
    /**
     * The elements to be returned by future calls to {@code next()}, with the first at the top of
     * the stack.
     */
    final Stack<E> nextElements = new Stack<>();

    /**

 *
 * <pre>{@code
 * // Helper function keeps victim stack-unreachable.
 * private WeakReference<Foo> fooWeakRef() {
 *   Foo x = ....;
 *   WeakReference<Foo> weakRef = new WeakReference<>(x);
 *   // ... use x ...
 *   x = null;  // Hint to the JIT that x is stack-unreachable
 *   return weakRef;
 * }
 * public void testFooLeak() {
 *   GcFinalization.awaitClear(fooWeakRef());

   */
  @Override
  public void close() throws IOException {
    Throwable throwable = thrown;

    // close closeables in LIFO order
    while (!stack.isEmpty()) {
      Closeable closeable = stack.removeFirst();
      try {
        closeable.close();
      } catch (Throwable e) {
        if (throwable == null) {
          throwable = e;
        } else {

 *
 * <pre>{@code
 * // Helper function keeps victim stack-unreachable.
 * private WeakReference<Foo> fooWeakRef() {
 *   Foo x = ....;
 *   WeakReference<Foo> weakRef = new WeakReference<>(x);
 *   // ... use x ...
 *   x = null;  // Hint to the JIT that x is stack-unreachable
 *   return weakRef;
 * }
 * public void testFooLeak() {
 *   GcFinalization.awaitClear(fooWeakRef());

   *   <li>If many such tasks are chained together (such as with {@code
   *       future.transform(...).transform(...).transform(...)....}), they may overflow the stack.
   *       (In simple cases, callers can avoid this by registering all tasks with the same {@link
   *       MoreExecutors#newSequentialExecutor} wrapper around {@code directExecutor()}. More

    checkArgument(value > 0, "Not true that %s is positive.", value);
    return value;
  }

  /**
   * An enum representing the state of a node during DFS. {@code PENDING} means that the node is on
   * the stack of the DFS, while {@code COMPLETE} means that the node and all its successors have
   * been already explored. Any node that has not been explored will not have a state at all.
   */
  private enum NodeVisitState {