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Date: Sat, 29 Jun 2019 09:57:44 +0200
Message-ID: <CAF+90c_8Yr7m+n1ys6g10EccSM31TT=XFtAm82bQai9XV9v8wA@mail.gmail.com>
To: CHU Zhaowei <me@jhdxr.com>
Cc: Stanislav Malyshev <smalyshev@gmail.com>, Benjamin Morel <benjamin.morel@gmail.com>, 
	PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Memory leak in eval()'d code
From: nikita.ppv@gmail.com (Nikita Popov)

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On Sat, Jun 29, 2019 at 9:07 AM CHU Zhaowei <me@jhdxr.com> wrote:

> I think we missed the point here. Clousre, or anonymous class, should not
> be considered as normal class. We expect normal class existing once we
> declare it till end of script. However, for anonymous class, it's usually
> used within certain scope, so not only the instances, the class itself
> should be included in the GC as well.
> I guess the problem here is we didn't GC the space for definition of
> anonymous classes.
>
> Regards,
> CHU Zhaowei
>

As Johannes already pointed out, we cannot garbage collect anonymous class
definitions due to the existence of opaque references. A simple example of
code that currently works:

    $obj = eval('return new class {}');
    $class = get_class($obj); // create opaque reference
    unset($obj); // drop last direct reference
    $obj = new $class;

In the end, an anonymous class is essentially a class with a random name
and some inline construction sugar, but apart from that does not differ
from ordinary classes. (I've also seen some calls to allow syntax like
$class = class {}; that would make that even more obvious.)

The situation here would be different if we had first-class classes and did
not refer to classes by name. But as-is, I don't think garbage collecting
anonymous classes is a possibility.

Nikita

> -----Original Message-----
> > From: Stanislav Malyshev <smalyshev@gmail.com>
> > Sent: Saturday, June 29, 2019 6:52 AM
> > To: Benjamin Morel <benjamin.morel@gmail.com>
> > Cc: PHP Internals <internals@lists.php.net>
> > Subject: Re: [PHP-DEV] Memory leak in eval()'d code
> >
> >
> >
> > On 6/28/19 3:37 PM, Benjamin Morel wrote:
> > >     That's not a "leak". You create new objects (in this case,
> classes),
> > >     they take memory.
> > >
> > >
> > > Why do they not "leak" memory without eval() then? Replace with
> > > `$object = new class {};` and memory usage stays flat.
> > > There has do be some kind of garbage collection for these anonymous
> classes.
> >
> > AFAIR this does not create new classes, since it's the same code, and
> same code
> > means same class. But eval() has new code every time, thus new class.
> Generally
> > I don't think PHP has any operation that can destroy an existing class.
> It won't be
> > easy too since you don't know whether there are any objects of this class
> > around (unless you're in shutdown).
> >
> > --
> > Stas Malyshev
> > smalyshev@gmail.com
> >
> > --
> > PHP Internals - PHP Runtime Development Mailing List To unsubscribe,
> visit:
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> >
>
>
>
>
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