// The results of all other inputs are then ignored (except for logging any failures).
      boolean completedWithFailure = setException(throwable);
      if (!completedWithFailure) {
        // Go up the causal chain to see if we've already seen this cause; if we have, even if
        // it's wrapped by a different exception, don't log it.
        boolean firstTimeSeeingThisException = addCausalChain(getOrInitSeenExceptions(), throwable);