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Date: Sun, 30 Jul 2017 11:44:05 +0800
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To: Nicolas Grekas <nicolas.grekas@gmail.com>
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Subject: Re: [PHP-DEV] Don't add simple objects to GC's roots
From: i@lvht.net (Haitao Lv)

Hi, internals,

> On 26 Jul 2017, at 22:57, Nicolas Grekas <nicolas.grekas@gmail.com> =
wrote:
>=20
> I'm hitting more and more the GC threshold in projects I work on (the =
"10k
> roots" one), leading to high CPU usage. Usually, the GC finds nothing =
to
> clean, so this is just a waste of CPU.

More and more php frameworks use object/array as an global container to =
store
config, and these container variable will be used every where, but =
seldom
introduce the circular reference. Apart from this, these container =
variable
will always be a huge tree, so iterate them will lead to high CPU usage.

> There is a way to work around: just call gc_disable(). But this means
> dealing with side effects of the engine in userland. Moreover, this =
also
> means leaking memory, since meanwhile roots are not populated.

In PHP-7.2, the GC_COLLECTABLE flag has been moved into the gc struct, =
and
this make it possible to prevent gc trace for certain zval.

So I propose to make the gc_disable function accept one zval reference =
as
parameter. And if gc_disable get that zval, gc_disable just drop the =
zval=E2=80=99s
GC_COLLECTABLE flag, which will hint the PHP gc not to trace that zval.

Here is my patch https://github.com/php/php-src/pull/2665/files, and a =
demo,

<?php
function hi($a)
{
    return $a->name;
}

$a =3D new stdclass;
$a->name =3D 'foo';

gc_disable($a);

hi($a); // these will change the refcount of $a, but never trace gc=