My wordpress plugin is beeing called twice

Question

I'm creating a WordPress plugin, and by debugging, I noticed its being called twice on each request. My plugin code is like this:

class Br1E_EngenhariaPlugin{
   (...)
}

new Br1E_EngenhariaPlugin(); // A breakpoint here is called twice on each request

Debugging the code I see that the problem is that the wp-load.php file is being called twice. The first time the callstack started at index.php:

If I hit continue, it will stop again at the same breakpoint, this time the callstack started at wp-cron.php:

I tried to make my class a singleton, by using a static variable to ensure the class is loaded only once:

class Br1E_EngenhariaPlugin{
    public static function LoadOnce() : Br1E_EngenhariaPlugin
    {
        if (self::$pluginInstance == null)
            self::$pluginInstance = new Br1E_EngenhariaPlugin();

        //register_activation_hook( __FILE__, array($br1Engenharia, 'install') );
        return self::$pluginInstance;
    }
    (...)
}

Br1E_EngenhariaPlugin::LoadOnce();

But it didn't work. The $pluginInstance static variable is null on the second time it's called, it's like it's a different request.

Answer 1

And yes, it is a different HTML request called from spawn_cron() in the file wp-includes/cron.php:

$result = wp_remote_post( $cron_request['url'], $cron_request['args'] );

Here $cron_request['uri'] contains http://your-site.com/wp-cron.php. And you can see it in the second call stack.

wp_cron in the file wp-includes/cron.php is hooked on every' init' event. Then, if any cron jobs are to be executed, spawn_cron() is called, producing an independent HTML request to the site.