V4 extends @Nullable Object,
          V5 extends @Nullable Object>
      Combiner5<V1, V2, V3, V4, V5> whenAllSucceed(
          ClosingFuture<V1> future1,
          ClosingFuture<V2> future2,
          ClosingFuture<V3> future3,
          ClosingFuture<V4> future4,
          ClosingFuture<V5> future5) {
    return new Combiner5<>(future1, future2, future3, future4, future5);
  }

  /**

    /*
     * Futures should be collected even if combiner never runs. This is kind of a silly test, since
     * the combiner is almost certain to hold its own reference to the futures, and a real app would
     * hold a reference to the executor and thus to the combiner. What we really care about is that
     * the futures are released once the combiner is done running. But we happen to provide this
     * earlier cleanup at the moment, so we're testing it.

    /*
     * Futures should be collected even if combiner never runs. This is kind of a silly test, since
     * the combiner is almost certain to hold its own reference to the futures, and a real app would
     * hold a reference to the executor and thus to the combiner. What we really care about is that
     * the futures are released once the combiner is done running. But we happen to provide this
     * earlier cleanup at the moment, so we're testing it.