}

    // This implementation is patterned after ConcurrentHashMap, but without the locking. The only
    // way for it to return a false negative would be for the target value to jump around in the map
    // such that none of the subsequent iterations observed it, despite the fact that at every point
    // in time it was present somewhere int the map. This becomes increasingly unlikely as

   *
   * <p>If the function throws an exception, that exception is used as the result of the derived
   * {@code ClosingFuture}. But if the exception is thrown after the function creates a {@code
   * ClosingFuture}, then none of the closeable objects in that {@code ClosingFuture} will be
   * closed.
   *
   * <p>Usage guidelines for this method:
   *
   * <ul>

    }

    // This implementation is patterned after ConcurrentHashMap, but without the locking. The only
    // way for it to return a false negative would be for the target value to jump around in the map
    // such that none of the subsequent iterations observed it, despite the fact that at every point
    // in time it was present somewhere int the map. This becomes increasingly unlikely as