public final void addTearDown(TearDown tearDown) {
    synchronized (stack) {
      stack.addFirst(checkNotNull(tearDown));
    }
  }

  /** Causes teardown to execute. */
  public final void runTearDown() {
    List<Throwable> exceptions = new ArrayList<>();
    List<TearDown> stackCopy;
    synchronized (stack) {
      stackCopy = Lists.newArrayList(stack);
      stack.clear();
    }
    for (TearDown tearDown : stackCopy) {

    }

    return builder.buildOrThrow();
  }

  /**
   * Parses a trie node and returns the number of characters consumed.
   *
   * @param stack The prefixes that precede the characters represented by this node. Each entry of
   *     the stack is in reverse order.
   * @param encoded The serialized trie.
   * @param start An index in the encoded serialized trie to begin reading characters from.

     * setException(stackOverflowError) would fail:
     *
     * - If the stack overflowed before set()/setValue() could even store the result in the output
     * Future, then a call setException() would likely also overflow.
     *
     * - If the stack overflowed after set()/setValue() stored its result, then a call to
     * setException() will be a no-op because the Future is already done.

    private final Deque<Iterator<T>> stack;

    PreOrderIterator(T root) {
      this.stack = new ArrayDeque<>();
      stack.addLast(Iterators.singletonIterator(checkNotNull(root)));
    }

    @Override
    public boolean hasNext() {
      return !stack.isEmpty();
    }

    @Override
    public T next() {
      Iterator<T> itr = stack.getLast(); // throws NSEE if empty

 *
 * <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());

  /** Logger to log exceptions caught when running runnables. */
  private static final LazyLogger log = new LazyLogger(ExecutionList.class);

  /**
   * The runnable, executor pairs to execute. This acts as a stack threaded through the {@link
   * RunnableExecutorPair#next} field.
   */
  @GuardedBy("this")
  @CheckForNull
  private RunnableExecutorPair runnables;

  @GuardedBy("this")
  private boolean executed;

      log.get()
          .log(
              Level.SEVERE,
              "SafeAtomicHelper is broken!",
              thrownAtomicReferenceFieldUpdaterFailure);
    }
  }

  /** Waiter links form a Treiber stack, in the {@link #waiters} field. */
  private static final class Waiter {
    static final Waiter TOMBSTONE = new Waiter(false /* ignored param */);

    @CheckForNull volatile Thread thread;

   */
  @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());

      fail();
    } catch (CancellationException expected) {
      // There should be two CancellationException chained together.  The outer one should have the
      // stack trace of where the get() call was made, and the inner should have the stack trace of
      // where the immediateCancelledFuture() call was made.
      List<StackTraceElement> stackTrace = ImmutableList.copyOf(expected.getStackTrace());