android/guava/src/com/google/common/util/concurrent/AggregateFuture.java
private static boolean addCausalChain(Set<Throwable> seen, Throwable t) {
    for (; t != null; t = t.getCause()) {
      boolean firstTimeSeen = seen.add(t);
      if (!firstTimeSeen) {
        /*
         * We've seen this, so we've seen its causes, too. No need to re-add them. (There's one case
         * where this isn't true, but we ignore it: If we record an exception, then someone calls
         * initCause() on it, and then we examine it again, we'll conclude that we've seen the whole
         * chain before when it fact we haven't. But this should be rare.)
         */
        return false;
      }
    }
    return true;
  }
private static boolean addCausalChain(Set<Throwable> seen, Throwable t) {
    for (; t != null; t = t.getCause()) {
      boolean firstTimeSeen = seen.add(t);
      if (!firstTimeSeen) {
        /*
         * We've seen this, so we've seen its causes, too. No need to re-add them. (There's one case
         * where this isn't true, but we ignore it: If we record an exception, then someone calls
         * initCause() on it, and then we examine it again, we'll conclude that we've seen the whole
         * chain before when it fact we haven't. But this should be rare.)
         */
        return false;
      }
    }
    return true;
  }
Adds the chain to the seen set, and returns whether all the chain was new to us.