private Combiner(boolean allMustSucceed, Iterable<? extends ClosingFuture<?>> inputs) {
      this.allMustSucceed = allMustSucceed;
      this.inputs = ImmutableList.copyOf(inputs);
      for (ClosingFuture<?> input : inputs) {
        input.becomeSubsumedInto(closeables);
      }
    }

    /**