Re: Use "ropes" for string concatenation

On Tue, Mar 24, 2015 at 1:14 PM, Xinchen Hui <xinchen.h@zend.com> wrote: > Hey: > > On Tue, Mar 24, 2015 at 2:04 PM, Pierre Joye <pierre.php@gmail.com> wrote: >> On Tue, Mar 24, 2015 at 1:01 PM, Xinchen Hui <xinchen.h@zend.com> wrote: >>> Hey: >>> >>> On Tue, Mar 24, 2015 at 1:54 PM, Pierre Joye <pierre.php@gmail.com> wrote: >>>> On Tue, Mar 24, 2015 at 12:35 PM, Xinchen Hui <xinchen.h@zend.com> wrote: >>>>> Hey: >>>>> >>>>> On Tue, Mar 24, 2015 at 1:31 PM, Pierre Joye <pierre.php@gmail.com> >>>>> wrote: >>>>>> hi! >>>>>> >>>>>> On Tue, Mar 24, 2015 at 5:41 AM, Dmitry Stogov <dmitry@zend.com> >>>>>> wrote: >>>>>>> Hi, >>>>>>> >>>>>>> Recently, Xinchen and me worked on optimization that eliminates useless >>>>>>> reallocations and copying during string concatenation (ZEND_ADD_STRING >>>>>>> and >>>>>>> family + ZEND_CONCAT). >>>>>>> >>>>>>> The idea comes from ropes, but adopted especially for our needs. >>>>>>> Rope is popular data structure in languages with immutable strings. >>>>>>> >>>>>>> http://en.wikipedia.org/wiki/Rope_%28data_structure%29 >>>>>>> >>>>>>> We don't try to use ropes everywhere in the engine (at least >>>>>>> it's too later >>>>>>> for 7.0), only for concatenation. >>>>>>> >>>>>>> The first branch uses ropes only instead of ZEND_ADD_STRING and family. >>>>>>> This must be safe. The only problem is possible memory leaks on >>>>>>> exception >>>>>>> (but we already have this problem anyway). The simplest way to >>>>>>> understand >>>>>>> the patch - read code for new opcodes in zend_vm_def.h. >>>>>>> >>>>>>> >>>>>>> https://github.com/php/php-src/pull/1194/files >>>>>>> >>>>>>> The second branch in addition uses ropes for series of ZEND_CONCAT. It >>>>>>> disables calls to do_operation(ZEND_CONCAT) handler of custom internal >>>>>>> classes. >>>>>>> >>>>>>> >>>>>>> https://github.com/php/php-src/pull/1195/files >>>>>>> >>>>>>> Both make slight speed improvement (first +0.3%, second +0.6% on >>>>>>> wordpress >>>>>>> home page). >>>>>>> >>>>>>> We don't currently use ability to override CONCAT behavior in >>>>>>> internal >>>>>>> classes, and I'm not sure if it may be useful at all. (For example >>>>>>> Lua >>>>>>> doesn't provide concat meta-method). May be remove it? >>>>>>> >>>>>>> Thoughts and comments are welcome. >>>>>> >>>>>> Great work! :) >>>>>> >>>>>> Do you expect similar gain for other ops? >>>>>> >>>>>> I wonder if it would not be better to target 7.1 for that, adding it >>>>>> for other string operations, in one go. Most of the current patch is >>>>>> self contained, it adds quite some complexity to the engine for these >>>>>> operations only and it is not a small change at this stage (post >>>>>> features freeze). It sounds like a possible maintenance pain. Taking >>>>> Actually, it's not. >>>>> >>>>> previously we have ADD_STRING/CHAR/VAR and CONCAT >>>>> >>>>> the 2nd branch cleanup these, and now we only deal with one type concat_list. >>>>> :) >>>> >>>> Right, it simplifies part of the existing implementation and add some >>>> complexities to other. It only adds this OP and keep other with the >>>> "old" implementation, that's actually the only part where I am not >>>> totally convinced. It may make sense to do it all at once, if that's >>>> the long term plan, easier to maintain. >>>> >>>> But if we do prefer to add this now, then the sooner the better, it >>>> may have some hard to catch bugs. Now, we have one issue, we cannot >>>> have a RFC (deadline behind us) and this is still a rather big change >>>> :/ >>> from user land. this won't change anything.. >> >> Nothing to do with userland or not but code stabilization > In that case, yeah. you might be right. > > but from my opinion, simpler always means easier for maintaining.... > > anyway, I hope this could be merged to 7.0(the second branch) :) Me too :) However I do not want to have double standards. We want a strict time stable to ensure the delivery of 7 final in time. Other RFCs are less intrusive (read, more self contained) and have been rejected. It is not very correct in my opinion. I do not mind much in this case as we can see this patch as part as the white card we gave when we accepted phpng, but I like to hear other voices as well. Cheers, -- Pierre @pierrejoye | http://www.libgd.org