Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:75149
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain zend.com designates 209.85.220.178 as permitted sender)
MIME-Version: 1.0
Date: Mon, 30 Jun 2014 23:06:06 +0400
Message-ID: <CA+9eiLtCyuMVN-CN_hnLCCij4nymUiKEa26K_S_qM1PN-g-4HA@mail.gmail.com>
To: Bob Weinand <bobwei9@hotmail.com>
Cc: Xinchen Hui <xinchen.h@zend.com>, David Soria Parra <dsp@php.ne>, Julien Pauli <jpauli@php.ne>, 
	PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=089e0122f736eee10d04fd125902
Subject: Wired constant expression syntax and bug
From: dmitry@zend.com (Dmitry Stogov)

--089e0122f736eee10d04fd125902
Content-Type: text/plain; charset=UTF-8

Hi Bob,

I'm wondered why you introduced this wired syntax in PHP-5.6.

class FooBar {
               const bar = ["bar" => 3]["bar"];
}

It wasn't a part of RFC, it wasn't covered by tests, and it actually
doesn't make a lot of sense. May be it's better to remove it?

Also I found a constant expression related bug, that leads to unpredictable
crashes from time to time. Previously we had IS_CONSTANT_ARRAY that was
handled in a special way. When you replaced it with IS_ARRAY, you missed
this handling, and I missed it as well when reviewed your patch. Now
IS_ARRAY constants might be incompletely copied from OPCache shared memory
and modified (incremented/decremented reference counter) directly in SHM.
Such modifications occur in simultaneously running processes and this
finally leads to crash on some race condition.

It's possible to emulate the problem running the following script with
opcache.protect_memory=1

<?php
function foo($query = NULL, array $exclude = array('q')) {}
foo();
?>

I propose a simple fix: https://gist.github.com/dstogov/b73884e252b376957ebc
Please review and apply if agree.

Thanks. Dmitry.

--089e0122f736eee10d04fd125902--