Postponed blog detection on WP >= 4.6

[stodorovic]

• Uses is_multisite. It's safe because it's defined in wp-includes/load.php.
• WordPress 4.6 introduces hook ms_loaded ( This action fires after multisite's bootstrap has finished and when the $current_site and $current_blog globals are populated). Running of function wp_cache_serve_cache_file is little postponed to we can get correct blog's domain and path (It loads few more files - probably 15-30ms more for multisite installations before serving file).

[donnchawp]

It simplifies things but does it fix a problem on MS sites?

[stodorovic]

It should be first step. Main change is:

if ( is_multisite() && $wpsc_wp_gte_46 && empty( $wp_super_cache_late_init ) ) {
	add_action( 'ms_loaded', 'wp_cache_serve_cache_file' );
}

wp_cache_serve_cache_file runs again wp-cache-base.php and get correct blog_id. Also WP_ALLOW_MULTISITE isn't good for detection ( #97 - correct constant is MULTISITE and is_multisite uses it).

For test, I've added code:

        // Fixes $blogcacheid and $blog_cache_dir if ms-settings.php is loaded.
        if ( is_multisite() && is_object( $current_blog ) ) {
                $old_blogcacheid =  $blogcacheid;
                $old_blog_cache_dir = $blog_cache_dir;
                require WPCACHEHOME . 'wp-cache-base.php';
                if ( $old_blogcacheid !=  $blogcacheid || $old_blog_cache_dir = $blog_cache_dir ) {
                        $duration = wp_cache_microtime_diff($GLOBALS['wp_start_time'], microtime()) * 1000;
                        $duration = sprintf("%.0f", $duration);
                        wp_cache_debug( 'Blog ID/Dir changed (ms_loaded delay - '.$duration.'ms): '. $old_blogcacheid.'=>'.$blogcacheid.' '.$old_blog_cache_dir.'=>'.$blog_cache_dir );
                }
        }

One example:
http://www.example.com/category/test

17:20:23 5467 /category/test/ Blog ID/Dir changed (ms_loaded delay - 26ms): category=>blog /home/.../wp-content/cache/blogs/category/=>/home/.../wp-content/cache/blogs/blog/

Main issue is "delete cache" (these blogs - category in example don't exist). I'm not sure for other side effects.

Anyway, it needs more testing, but I think that this will fix main issues. I'm still working on it and I'm cleaning old code. Also, I'll try to re-read issues on wordpress.org. Maybe I figure out more details.

[donnchawp]

I merged #592 first because this touches a lot of code and looks like it'll be hard to test fully.

I also want to get a quick fix out for the fatal error updating posts.

[stodorovic]

No problem. I agree that's hard to check. I'm planning to split into couple PRs.

[stodorovic]

I just created #600 which contains one part of this PR.

[stodorovic]

Closing this in favor of #600, #602 and #606.