// 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<>();

    /**

     * 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.

 *
 * <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;

      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());

      setFutureSuccess.set(false);
      cancellationSuccess.set(false);
      finalResults.clear();
    }
    executor.shutdown();
  }

  // In a previous implementation this would cause a stack overflow after ~2000 futures chained
  // together.  Now it should only be limited by available memory (and time)
  public void testSetFuture_stackOverflow() {
    SettableFuture<String> orig = SettableFuture.create();

   * thrown by {@linkplain MoreExecutors#directExecutor direct execution}) will be caught and
   * logged.
   *
   * <p>Note: If your listener is lightweight -- and will not cause stack overflow by completing
   * more futures or adding more {@code directExecutor()} listeners inline -- consider {@link
   * MoreExecutors#directExecutor}. Otherwise, avoid it: See the warnings on the docs for {@code

      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());

      super(message);
    }

    @Override
    public synchronized Throwable fillInStackTrace() {
      setStackTrace(new StackTraceElement[0]);
      return this; // no stack trace, wouldn't be useful anyway
    }
  }

  @Override
  @CheckForNull
  protected String pendingToString() {
    ListenableFuture<? extends V> localInputFuture = delegateRef;