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) >> > > > > >> > > > >> > > >> > >> > >
