Zero extra memory used when resizing image

[RV7PR]

Description

I have a large image on a production server, and when I try to resize it using imagecreatefromjpeg(), it exceeds the memory limit of 768MB. Strangely, when I test this exact same image in my development environment, it uses ZERO extra memory; even with a memory_limit set to 10MB, the image resizes without any issues. how does this work?

It's a large image (9449x37796 / 7mb) so exceeding the limit was expected though not the zero memory used on my dev env. (or at least not memory used by the php process I guess)

PHP Version

PHP 8.4.3

Operating System

CentOS 9 Stream

[iluuu1994]

gd doesn't seem to be using PHPs memory allocator, but the system allocator. Looking at the source code, it doesn't seem like gd doesn't provide an option to configure the allocator. I'm not sure if they would be interested in adding that, but this might also lead to regressions due to incorrectly configured memory limits. /cc @cmb69

https://github.com/libgd/libgd/blob/0b8d70805d6f0b53a88902826ddc02208f8e32a1/src/gdhelpers.c#L67-L82

[cmb69]

From https://www.php.net/manual/en/intro.image.php:

Caution
While the bundled version of the GD library uses the Zend memory manager to allocate memory, system versions do not, so that memory_limit does not apply.

To use ZendMM for external (system) libgd, libgd would need to offer custom allocators (libgd/libgd#335), and these would need to be widely available.

So nothing we can fix for now.

[cmb69]

Note that we could keep this ticket open and tag with "waiting for third-party library fix", but I wouldn't hold my breath that this will happen in the next few years. So closed as "won't fix" (since we don't have "can't fix").

[RV7PR]

Thx, it's now clear to me where this difference comes from.