Hi Tagir, Well spotted. We made an exception when the spliterator covers no elements:
https://bugs.openjdk.java.net/browse/JDK-8022797 http://hg.openjdk.java.net/jdk8/jdk8/jdk/rev/737b6c298d81 I thought i could get away solely with a specification change to allow reuse of an empty spliterator implementation. But, as you show it pops up in certain cases that aggregate two or more streams. In hindsight i somewhat regret this decision as it makes general processing more difficult :-( In this case we should fix Stream.concat to check if a spliterator reporting SIZED is empty, which will allow us to optimize the concatenation [1]. Paul. P.S. I still have a bunch of your stuff in my queue to process, sorry it’s taking so long,i will get to them in the next couple of weeks, but i need to process some other stuff first. [1] https://bugs.openjdk.java.net/browse/JDK-8022805 On 6 Sep 2015, at 12:21, Tagir F. Valeev <amae...@gmail.com> wrote: > Hello! > > As Paul Sandoz pointed out in the "Custom spliterator for > Collections.nCopies(n, obj).stream()" discussion, the > List.spliterator() is specified to be ORDERED. However > Collections.emptyList().spliterator() violates this specification: > > System.out.println(Collections.emptyList() > .spliterator().hasCharacteristics(Spliterator.ORDERED)); > // prints false > > This becomes critical if I want to concatenate streams from the two > lists returned from two different methods (one of which returned > emptyList) and process the result in parallel. For example: > > List<Integer> list1 = IntStream.range(0, > 100).boxed().collect(Collectors.toList()); > List<Integer> list2 = Collections.emptyList(); > System.out.println(Stream > .concat(list1.stream(), list2.stream()).parallel() > .filter(x -> x >= 0).limit(10).collect(Collectors.toList())); > > This code unexpectedly prints some random subset. This can be fixed by > replacing list2 with > > List<Integer> list2 = Arrays.asList(); > > As Arrays.asList().spliterator() is ordered, the resulting stream is > ordered as well, so we see [0, ..., 9] as expected. > > Looks like a bug in emptyList() implementation. > > With best regards, > Tagir Valeev. >
