Hmph.. You delegate to the lower iterator entirely. Why not just return it in the first place?
On Sun, Apr 14, 2013 at 5:27 PM, Robin Anil <[email protected]> wrote: > I am working on a patch. Here is a sample. This one is for RASV. I put > Dan's example as a test case. > > > > 1. private final class NonDefaultIterator implements Iterator<Element> > { > 2. private final class NonDefaultElement implements Element { > 3. @Override > 4. public double get() { > 5. return mapElement.get(); > 6. } > 7. > 8. @Override > 9. public int index() { > 10. return mapElement.index(); > 11. } > 12. > 13. @Override > 14. public void set(double value) { > 15. invalidateCachedLength(); > 16. mapElement.set(value); > 17. } > 18. } > 19. > 20. private final NonDefaultElement element = > newNonDefaultElement(); > 21. private final Iterator<MapElement> iterator; > 22. private MapElement mapElement; > 23. > 24. private NonDefaultIterator() { > 25. this.iterator = values.iterator(); > 26. } > 27. > 28. @Override > 29. public boolean hasNext() { > 30. return iterator.hasNext(); > 31. } > 32. > 33. @Override > 34. public Element next() { > 35. mapElement = iterator.next(); > 36. return element; > 37. } > 38. > 39. @Override > 40. public void remove() { > 41. throw new UnsupportedOperationException(); > 42. } > 43. } > 44. > > > > Robin Anil | Software Engineer | +1 312 869 2602 | Google Inc. > > > On Sun, Apr 14, 2013 at 7:04 PM, Ted Dunning <[email protected]> > wrote: > > > Well... current iterator style with a non-side-effecting version of > > hasNext(), of course. > > > > Reusing the container is OK if the performance hit is substantial. > > > > > > On Sun, Apr 14, 2013 at 5:02 PM, Robin Anil <[email protected]> > wrote: > > > > > Also the Tests crash due to excessive GC. The performance degradation > > there > > > is very visible(my cpu spikes up). I think there is good case for the > > > current iteration style, just that we have to, not use the java > Iterator > > > contract and confuse clients. > > > > > > Robin Anil | Software Engineer | +1 312 869 2602 | Google Inc. > > > > > > > > > On Sun, Apr 14, 2013 at 6:59 PM, Robin Anil <[email protected]> > > wrote: > > > > > > > Yes. All final. > > > > > > > > Robin Anil | Software Engineer | +1 312 869 2602 | Google Inc. > > > > > > > > > > > > On Sun, Apr 14, 2013 at 6:55 PM, Ted Dunning <[email protected] > > > >wrote: > > > > > > > >> Did you mark the class and fields all as final? > > > >> > > > >> That might help the compiler realize it could in-line stuff and > avoid > > > the > > > >> constructor (not likely, but possible) > > > >> > > > >> > > > >> On Sun, Apr 14, 2013 at 4:52 PM, Robin Anil <[email protected]> > > > wrote: > > > >> > > > >> > With a new immutable Element in the iterator, the iteration > behavior > > > is > > > >> > corrected but. There is a performance degradation of about 10% and > > > >> > nullifies what I have done with the patch. > > > >> > > > > >> > See > > > >> > > > > >> > > > > >> > > > > > > https://docs.google.com/spreadsheet/ccc?key=0AhewTD_ZgznddGFQbWJCQTZXSnFULUYzdURfWDRJQlE#gid=1 > > > >> > > > > >> > Robin Anil | Software Engineer | +1 312 869 2602 | Google Inc. > > > >> > > > > >> > > > > >> > On Sun, Apr 14, 2013 at 11:28 AM, Ted Dunning < > > [email protected]> > > > >> > wrote: > > > >> > > > > >> > > Yeah... but we still have to fix the iterator. > > > >> > > > > > >> > > > > > >> > > On Sun, Apr 14, 2013 at 8:58 AM, Robin Anil < > [email protected] > > > > > > >> > wrote: > > > >> > > > > > >> > > > Here is an iteration style that works as is with today's > > behaviour > > > >> of > > > >> > > > hasNext > > > >> > > > > > > >> > > > 1. > > > >> > > > 2. Element thisElement = null; > > > >> > > > 3. Element thatElement = null; > > > >> > > > 4. boolean advanceThis = true; > > > >> > > > 5. boolean advanceThat = true; > > > >> > > > 6. > > > >> > > > 7. Iterator<Element> thisNonZero = > > this.iterateNonZero(); > > > >> > > > 8. Iterator<Element> thatNonZero = > x.iterateNonZero(); > > > >> > > > 9. > > > >> > > > 10. double result = 0.0; > > > >> > > > 11. while (true) { > > > >> > > > 12. *if (advanceThis) { > > > >> > > > * > > > >> > > > 13. * if (!thisNonZero.hasNext()) { > > > >> > > > * > > > >> > > > 14. * break; > > > >> > > > * > > > >> > > > 15. * } > > > >> > > > * > > > >> > > > 16. * thisElement = thisNonZero.next(); > > > >> > > > * > > > >> > > > 17. * } > > > >> > > > * > > > >> > > > 18. * if (advanceThat) { > > > >> > > > * > > > >> > > > 19. * if (!thatNonZero.hasNext()) { > > > >> > > > * > > > >> > > > 20. * break; > > > >> > > > * > > > >> > > > 21. * } > > > >> > > > * > > > >> > > > 22. * thatElement = thatNonZero.next(); > > > >> > > > * > > > >> > > > 23. * }* > > > >> > > > 24. if (thisElement.index() == > thatElement.index()) { > > > >> > > > 25. > > > >> > > > 26. result += thisElement.get() * > > thatElement.get(); > > > >> > > > 27. advanceThis = true; > > > >> > > > 28. advanceThat = true; > > > >> > > > 29. } else if (thisElement.index() < > > > >> thatElement.index()) { > > > >> > > > 30. advanceThis = true; > > > >> > > > 31. advanceThat = false; > > > >> > > > 32. } else { > > > >> > > > 33. advanceThis = false; > > > >> > > > 34. advanceThat = true; > > > >> > > > 35. } > > > >> > > > 36. } > > > >> > > > > > > >> > > > > > > >> > > > On Sat, Apr 13, 2013 at 1:47 AM, Ted Dunning < > > > [email protected] > > > >> > > > > >> > > > wrote: > > > >> > > > > > > >> > > > > The caller is not at fault here. The problem is that > hasNext > > is > > > >> > > > advancing > > > >> > > > > the iterator due to a side effect. The side effect is > > > impossible > > > >> to > > > >> > > > avoid > > > >> > > > > at the level of the caller. > > > >> > > > > > > > >> > > > > Sent from my iPhone > > > >> > > > > > > > >> > > > > On Apr 12, 2013, at 12:22, Sean Owen <[email protected]> > > wrote: > > > >> > > > > > > > >> > > > > > I'm sure I did (at least much of) the AbstractIterator > > change > > > so > > > >> > > blame > > > >> > > > > > me... but I think the pattern itself is just fine. It's > used > > > in > > > >> > many > > > >> > > > > > places in the project. Reusing the value object is a big > win > > > in > > > >> > some > > > >> > > > > > places. Allocating objects is fast but a trillion of them > > > still > > > >> > adds > > > >> > > > > > up. > > > >> > > > > > > > > >> > > > > > It does contain a requirement, and that is that the caller > > is > > > >> > > supposed > > > >> > > > > > to copy/clone the value if it will be used at all after > the > > > next > > > >> > > > > > iterator operation. That's the 0th option, to just fix the > > > >> caller > > > >> > > > > > here. > > > >> > > > > > > > > >> > > > > > On Fri, Apr 12, 2013 at 7:49 PM, Ted Dunning < > > > >> > [email protected]> > > > >> > > > > wrote: > > > >> > > > > >> The contract of computeNext is that there are no side > > effects > > > >> > > visible > > > >> > > > > >> outside (i.e. apparent functional style). This is > required > > > >> since > > > >> > > > > >> computeNext is called from hasNext(). > > > >> > > > > >> > > > >> > > > > >> We are using a side-effecting style so we have a bug. > > > >> > > > > >> > > > >> > > > > >> We have two choices: > > > >> > > > > >> > > > >> > > > > >> a) use functional style. This will *require* that we > > > allocate a > > > >> > new > > > >> > > > > >> container element on every call to computeNext. This is > > best > > > >> for > > > >> > > the > > > >> > > > > user > > > >> > > > > >> because they will have fewer surprising bugs due to > reuse. > > > If > > > >> > > > > allocation > > > >> > > > > >> is actually as bad as some people think (I remain > skeptical > > > of > > > >> > that > > > >> > > > > without > > > >> > > > > >> tests) then this is a bad move. If allocation of totally > > > >> > ephemeral > > > >> > > > > objects > > > >> > > > > >> is as cheap as I think, then this would be a good move. > > > >> > > > > >> > > > >> > > > > >> b) stop using AbstractIterator and continue with the > re-use > > > >> style. > > > >> > > > And > > > >> > > > > add > > > >> > > > > >> a comment to prevent a bright spark from reverting this > > > change. > > > >> > (I > > > >> > > > > suspect > > > >> > > > > >> that the bright spark who did this in the first place was > > me > > > >> so I > > > >> > > can > > > >> > > > be > > > >> > > > > >> rude) > > > >> > > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > > > > > > > > > > > >
