FFI: A state is kept somewhere between two HTTP requst

[lyrixx]

Description

The following code:

<?php

class LibNotifyDriver
{
    private static FFI $ffi;

    public function send(): bool
    {
        $this->initialize();
        $notification = self::$ffi->notify_notification_new(
            'a title',
            'a body',
            null,
        );
        $value = self::$ffi->notify_notification_show($notification, null);
        self::$ffi->g_object_unref($notification);

        return $value;
    }

    private static function initialize(): void
    {
        if (isset(self::$ffi)) {
            return;
        }

        $header = <<<'C'
            typedef bool gboolean;
            typedef void* gpointer;
            typedef struct _NotifyNotification NotifyNotification;
            typedef struct _GTypeInstanceError GError;

            gboolean notify_init(const char *app_name);
            gboolean notify_is_initted (void);
            void notify_uninit (void);
            NotifyNotification *notify_notification_new(const char *summary, const char *body, const char *icon);
            gboolean notify_notification_show (NotifyNotification *notification, GError **error);
            void g_object_unref (gpointer object);
            C;

        $ffi = FFI::cdef($header, 'libnotify.so.4');

        if (!$ffi) {
            throw new RuntimeException('Unable to load libnotify');
        }

        self::$ffi = $ffi;

        if (!self::$ffi->notify_init('app')) {
            throw new RuntimeException('Unable to initialize libnotify');
        }

        if (!self::$ffi->notify_is_initted()) {
            throw new RuntimeException('Libnotify has not been initialized');
        }
    }
}

$driver = new LibNotifyDriver();
$driver->send();

Resulted in this output:

>…ire/dev/github.com/jolicode/JoliNotif(ffi) php -S 127.0.0.1:9999 test.php 
[Thu May 22 15:14:12 2025] PHP 8.4.7 Development Server (http://127.0.0.1:9999) started
[Thu May 22 15:14:14 2025] 127.0.0.1:42474 Accepted
[Thu May 22 15:14:14 2025] 127.0.0.1:42474 Closing
[Thu May 22 15:14:15 2025] 127.0.0.1:42480 Accepted

(process:2370852): GLib-GObject-WARNING **: 15:14:15.844: cannot register existing type 'NotifyNotification'

(process:2370852): GLib-CRITICAL **: 15:14:15.844: g_once_init_leave: assertion 'result != 0' failed

(process:2370852): GLib-GObject-CRITICAL **: 15:14:15.844: g_object_new_valist: assertion 'G_TYPE_IS_OBJECT (object_type)' failed

(process:2370852): libnotify-CRITICAL **: 15:14:15.844: notify_notification_show: assertion 'notification != NULL' failed

(process:2370852): GLib-GObject-CRITICAL **: 15:14:15.844: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
[Thu May 22 15:14:15 2025] 127.0.0.1:42480 Closing

But I expected this output instead:

>…ire/dev/github.com/jolicode/JoliNotif(ffi) php -S 127.0.0.1:9999 test.php 
[Thu May 22 15:14:12 2025] PHP 8.4.7 Development Server (http://127.0.0.1:9999) started
[Thu May 22 15:14:14 2025] 127.0.0.1:42474 Accepted
[Thu May 22 15:14:14 2025] 127.0.0.1:42474 Closing
[Thu May 22 15:14:15 2025] 127.0.0.1:42480 Accepted
[Thu May 22 15:14:15 2025] 127.0.0.1:42480 Closing

---

We found this issue via jolicode/JoliNotif#120

In cli, we had some troubles, so I refactored the code to allow only once instance. But with a web SAPI, it does not work. On the very first request, it works, but on the second one it does not.

I tested with the cli-server SAPI, and FPM SAPI

PHP Version

PHP 8.4.7 (cli) (built: May  9 2025 06:54:08) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.7, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.7, Copyright (c), by Zend Technologies
    with blackfire v1.92.32~linux-x64-non_zts84, https://blackfire.io, by Blackfire

Operating System

Ubuntu 22.04.5 LTS

[bwoebi]

Well, yes. That state is global, process bound. The PHP runtime has no idea of the lifecycle of any FFI-included libraries. The function of that library here seems to assume that it's only called once per process. That's your responsibility to maintain, not PHP's.

[lyrixx]

Thanks for the answer. But if FPM keeps a bound between every requests, How can I, at the PHP userland level, re-use this bound?

[lyrixx]

We managed to do that, and it work well. What would be awesome, is to be able to write such code:

try {
    $ffi = FFI::scope('libnotify');
} catch (\Throwable) {
    $ffi = FFI::load(__DIR__ . '/lib.h');
}

I said that, because we distribute a lib, and it would be more convenient