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Date: Tue, 24 Mar 2015 12:28:25 +0300
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To: Nikita Popov <nikita.ppv@gmail.com>
Cc: Xinchen Hui <xinchen.h@zend.com>, Joe Watkins <pthreads@pthreads.org>, 
	PHP Internals <internals@lists.php.net>
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Subject: Re: Use "ropes" for string concatenation
From: dmitry@zend.com (Dmitry Stogov)

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I thought about something like this :)
In my opinion UString is really not a proper way to implement Unicoide, but
I agree not break anything in current stage.
Anyway, please review the first PR (in my opinion it is safe to commit),
but you may find some other issues.

Thanks. Dmitry.



On Tue, Mar 24, 2015 at 12:11 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.
>
> Nikita
>

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