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Date: Mon, 30 Jun 2014 23:32:14 +0400
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To: Bob Weinand <bobwei9@hotmail.com>, PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Wired constant expression syntax and bug
From: dmitry@zend.com (Dmitry Stogov)

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OK. I'll commit the patch.

According to the wired syntax, note that your example code will make PHP at
first construct an array and then destroy it.

why not to write $var = DO ? "value1" : "value2";

it must be more clear and efficient.

In case you like to keep this new syntax in PHP-5.6 at least please cover
it with tests.
I'm not a big fun of it, but won't object if it can't make real harm.

Thanks. Dmitry.


On Mon, Jun 30, 2014 at 11:21 PM, Bob Weinand <bobwei9@hotmail.com> wrote:

> That syntax wasn't part of the RFC because it wasn't yet possible
> (existence of IS_CONSTANT_ARRAY at that time).
> Also the use case for that one is mainly:
>
> class Foo {
>         public $var = ["value1", "value2"][DO];
> }
>
> And then just write
> const DO = 0; (or 1)
>
> I don't exactly know at which point that conflicts with opcache. Or if
> that really fixes the bug.
> The copying itself in your patch looks fine, but please take the
> responsibility for it and apply it yourself.
>
> Thanks,
> Bob
>
> Am 30.6.2014 um 21:06 schrieb Dmitry Stogov <dmitry@zend.com>:
> > Hi Bob,
> >
> > I'm wondered why you introduced this wired syntax in PHP-5.6.
> >
> > class FooBar {
> >               const bar = ["bar" => 3]["bar"];
> > }
> >
> > It wasn't a part of RFC, it wasn't covered by tests, and it actually
> > doesn't make a lot of sense. May be it's better to remove it?
> >
> > Also I found a constant expression related bug, that leads to
> unpredictable
> > crashes from time to time. Previously we had IS_CONSTANT_ARRAY that was
> > handled in a special way. When you replaced it with IS_ARRAY, you missed
> > this handling, and I missed it as well when reviewed your patch. Now
> > IS_ARRAY constants might be incompletely copied from OPCache shared
> memory
> > and modified (incremented/decremented reference counter) directly in SHM.
> > Such modifications occur in simultaneously running processes and this
> > finally leads to crash on some race condition.
> >
> > It's possible to emulate the problem running the following script with
> > opcache.protect_memory=1
> >
> > <?php
> > function foo($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.
>

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