@Override
          public @Nullable Void call() {
            if (currentFuture.get().set("set")) {
              numSuccessfulSetCalls.incrementAndGet();
            }
            awaitUnchecked(barrier);
            return null;
          }
        };
    Callable<@Nullable Void> completeExceptionallyRunnable =
        new Callable<@Nullable Void>() {