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Date: Tue, 24 Mar 2015 16:28:33 +0700
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To: Nikita Popov <nikita.ppv@gmail.com>
Cc: Joe Watkins <pthreads@pthreads.org>, PHP internals <internals@lists.php.net>, 
	Dmitry Stogov <dmitry@zend.com>, Xinchen Hui <xinchen.h@zend.com>
Content-Type: multipart/alternative; boundary=001a11c3bde81397a20512056803
Subject: Re: [PHP-DEV] Re: Use "ropes" for string concatenation
From: pierre.php@gmail.com (Pierre Joye)

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On Mar 24, 2015 4:11 PM, "Nikita Popov" <nikita.ppv@gmail.com> wrote:
>
> On Mon, Mar 23, 2015 at 11:41 PM, 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?
> >
>
> Overloading concat operator will be useful in the future for the
> implementation of the UString class, for example.

Indeed :)

Which will be 7.1, at best, no matter which one. Hence a bit my thoughts
about waiting a bit and spend more time on that, if other ops make sense
too.

But again, if everyone agrees, no issue to get that part in already.

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