How to properly restart Apache(mod-php) when updating FFI_LIB libraries in ffi.preload

[lajollah]

Description

apache(prefork) 2.4.62
php 8.2.28

I already have a properly functioning FFI configuration with connected libraries.

My question is whether a complete restart of the Apache process (full stop and then start) is always necessary when the library (.so) needs to be updated.

Once, to update the library, I overwrote the file at the path specified by FFI_LIB with an updated file and tried apachectl graceful. I confirmed that all Apache worker processes restarted, but the result showed that it was still referencing the old library rather than the updated one.

After some experimentation, I found that when I changed the FFI_LIB path in the header (.h) file configured in ffi.preload and then tried apachectl graceful, it successfully referenced the new library.

However, when I examined pmap -p <APACHE PID>, I observed the following two mappings:

00007fcce5531000     20K r---- /home/abc/xyz.so.02
00007fcce5536000    252K r-x-- /home/abc/xyz.so.02
00007fcce5575000     52K r---- /home/abc/xyz.so.02
00007fcce5582000     12K r---- /home/abc/xyz.so.02
00007fcce5585000      4K rw--- /home/abc/xyz.so.02
...
00007fccf36bc000     20K r---- /home/abc/xyz.so.01
00007fccf36c1000    252K r-x-- /home/abc/xyz.so.01
00007fccf3700000     52K r---- /home/abc/xyz.so.01
00007fccf370d000     12K r---- /home/abc/xyz.so.01
00007fccf3710000      4K rw--- /home/abc/xyz.so.01

The Apache process was running normally, and the library functions were working properly, but I'm still unsure if this result is normal. If I were to update 100 times, would I end up with about 100 such mappings?

When using ffi.preload and needing to update the connected library, which of the following approaches is correctly understood?

1. Use symbolic links for changes. (At least from what I've observed, this doesn't guarantee consistent behavior.)
   e.g.,

   xyz.so -> /home/abc/xyz.so.01 (symbolic link)
   xyz.so.01
   xyz.so.02
   

2. Always change the FFI_LIB path in the ffi.preload header file.
   e.g.,

   #define FFI_LIB "/home/abc/xyz.so.0.2"
   

3. Always use apachectl stop followed by start for updates.
   e.g.,

   $ sudo apachectl stop && sudo apachectl start
   

Approach #3 works without issues, but completely stopping and starting the master process is burdensome in a live server on-premises environment.

It would be great if there's a general method that can be used with apachectl graceful.
Below is a simplified version of my php.ini and ffi.preload header file for testing:

zend_extension=opcache
extension=ffi
ffi.enable=preload
ffi.preload=/home/abc/preload.h
opcache.enable=1
opcache.preload_user=nobody
opcache.preload=/home/abc/preload.php

#define FFI_SCOPE "XYZ"
#define FFI_LIB "/home/abc/xyz.so"
#include <stdint.h>
void xyz_hello_world(void);
int32_t xyz_this_year(void);
size_t xyz_multiply(int32_t v);