Alexandre Gustave Eiffel

Commemorative stone
in Marmagen, Germany

Journey Into The Unknown

Do you dare to join?

What is "Bootstrapping"? (1/3)

• Code to prepare the environment

• Not part of the actual logic that solves a problem

• Often used to abstract away differences between platforms

What is "Bootstrapping"? (2/3)

What is "Bootstrapping"? (3/3)

General execution flow

Order of loading files (1/1)

Front-end request

Entry point
index.php
↓
Load WordPress environment and template
wp-blog-header.php
↓
Load the WordPress library
wp-load.php
↓
Set up the WordPress query
wp()
↓
Load the theme template
WPINC/template-loader.php

Order of loading files (2/2)

Back-end request

Entry point
wp-admin/index.php
↓
Load WordPress environment and template
wp-admin/admin.php
↓
Load the WordPress library
wp-load.php
↓
Set up the WordPress query
wp_dashboard()

Order of loading files (3/3)

Inside wp-load.php

Notable Constants

• ABSPATHPath to the root folder of the WordPress installation
• SHORT_INITShort-circuit WP loading to run a minimal system
• MULTISITEEnable multisite network
• IS_SUBDOMAIN_INSTALLWhether multisite is a subdomain or subfolder network
• WP_LANG_DIRPath to translation files
• DOING_AJAXCurrent request is an AJAX request
• IFRAME_REQUESTCurrent request is an IFrame request
• WP_INSTALLINGPart of the installation routine, skip plugins/theme

Full reference in wp-core-bootstrap/documentation on GitHub (WIP)

Notable Global Variables

• $blog_idID of currently active site in a network
• $pagenowCurrently active page
• $current_userCurrently active user
• $wpdbDatabase abstraction in use
• $wp_object_cacheCache abstraction in use
• $wp_queryCurrently active database query
• $wp_filterHooks registered through the Plugin API
• $current_siteCurrently active WP_Network
• $current_blogCurrently active WP_Site

Full reference in wp-core-bootstrap/documentation on GitHub (WIP)

Plugin API initialization

• Class declaration for WP_Hook is loaded early in wp-settings.php

• Fetches existing hooks from global $wp_filter, in case drop-ins have added filter manually before the Plugin API was ready

• Some hooks run before plugins, so can only be used by non-web runtimes:
  enable_loading_advanced_cache_dropin
enable_maintenance_mode
enable_wp_debug_mode_checks

• Huge list of hooks * preloaded through WPINC/default-filters.php

* (447 @ v4.8)

Pluggable Functionality (1/2)

Pluggable Files in WP_CONTENT_DIR ("drop-ins")

Pluggable Functionality (2/2)

Pluggable Functions in WPINC/pluggable.php

Database connection

• Direct dependence on MySQL *

• Abstracted through wpdb (leaky)

• Pluggable through WP_CONTENT_DIR/db.php

* this includes MariaDB, a MySQL fork

Custom database implementation (1/2)

• Provide WP_CONTENT_DIR/db.php that sets the global $wpdb to a custom instance

• Skips compatbility checks unless $wpdb->is_mysql returns true

• Class wpdb is already loaded, so custom implementation can extend if needed

Custom database implementation (2/2)

File WP_CONTENT_DIR/db.php:

                global $wpdb;

                class AwesomeDB extends wpdb {
                    const ANSWER = 42;

                    function db_version()    { return 'AwesomeDB 1.0'; }
                    function db_connect()    { return true; }
                    function query( $query ) { return static::ANSWER; }
                }

                $wpdb = new AwesomeDB();
            

Some alternative database implementations

• HyperDB by Automattic

• LudicrousDB by John James Jacoby

• SQLite Integration by Kojima Toshiyasu (abandoned?)

Caching setup

• Abstracted through wp_cache_* functions

• Used transparently for most queries

• Pluggable through WP_CONTENT_DIR/object-cache.php
  and WP_CONTENT_DIR/advanced-cache.php

Custom cache implementation (1/2)

• Provide WP_CONTENT_DIR/object-cache.php that sets the global $wp_object_cache to a custom instance and provides wp_cache_* functions

• Provide WP_CONTENT_DIR/advanced-cache.php if you need to proactively fiddle with the loading process

• Loading of the WP_CONTENT_DIR/advanced-cache.php file can be controlled through the 'enable_loading_advanced_cache_dropin' filter

Custom cache implementation (2/2)

                        // Override Cache API functions.
                        function wp_cache_get( ...$args ) {
                            $wp_object_cache->get( ...$args );
                        }
                        function wp_cache_set( ...$args ) {
                            $wp_object_cache->set( ...$args );
                        }
                        function wp_cache_delete( ...$args ) {
                            $wp_object_cache->delete( ...$args );
                        }
                        function wp_cache_flush() {
                            $wp_object_cache->flush();
                        }
                        ...
                        function wp_cache_init() {
                            $wp_object_cache = new AwesomeCache();
                        }
                    

                        // Provide actual implementation class.
                        // This can't extend WP_Object_Cache, as it won't
                        // have been declared.
                        class AwesomeCache {
                            // This is where we hold the awesomeness.
                            private $cache;

                            public function __construct() {
                                // Initialize awesomeness here.
                            }

                            public function get( ...$args ) {...}
                            public function set( ...$args ) {...}
                            public function delete( ...$args ) {...}
                            public function flush() {...}
                            ...
                        }
                    

Localization setup

Set WP_LANG_DIR to either WP_CONTENT_DIR/languages or WPINC/languages
↓
Load MO class for reading GetText translation files
↓
Load 'default' translated strings based on locale
↓
Set up $wp_locale global
↓
Initialize $wp_locale_switcher

Translations

• Stored in global array $l10n with the key being the text domain

• If a text domain was not found, it is loaded on demand (looking in WP_LANG_DIR first)

• If a text domain could not be loaded, an instance of NOOP_Translations is returned

Multisite identification and loading (1/2)

Declare functions to work with multisite tables and data
WPINC/ms-blogs.php
↓
Set up multisite environment
WPINC/ms-settings.php
↓
Declare functions to load multisite into memory
WPINC/ms-load.php
↓
Load default multisite constants
WPINC/ms-default-constants.php
↓
Load sunrise drop-in if it exists and SUNRISE has been defined
WP_CONTENT_DIR/sunrise.php
↓

Multisite identification and loading (2/2)

If either $current_site or $current_blog are not set yet...
↓
Extract domain from $_SERVER['HTTP_HOST']
↓
Extract path from $_SERVER['REQUEST_URI']
↓
If DOMAIN_CURRENT_SITE and PATH_CURRENT_SITE are defined, use these
↓
If we're dealing with a subfolder install, identify network first, then query network for site path
↓
If we're dealing with a subdomain install, identify site by exact domain and at most first segment of path
↓
In case of failure, trigger actions ms_network_not_found or ms_site_not_found

Sunrise drop-in (1/2)

• Loaded if the constant SUNRISE is set and the file WP_CONTENT_DIR/sunrise.php exists

• Allows control over multisite setup mechanism

• Deactivates the entirety of the detection on the previous slide if it sets $current_site and $current_blog

• Entry point for domain mapping

Sunrise drop-in (2/2)

                        // This is your customized wp-config.php file
                        // that contains your install configuration.

                        // [ ... ]

                        // Activate sunrise mechanism.
                        define( 'SUNRISE', true );

                        // [ ... ]
                    

                        // This file is responsible for detecting what
                        // network and site to use for a given request.

                        global $current_site, $current_blog;

                        // This is actually the current WP_Network.
                        $current_site = WP_Network::get_instance(
                            custom_logic_to_detect_network_id()
                        );

                        // This is the current WP_Site.
                        $current_blog = WP_Site::get_instance(
                            custom_logic_to_detect_site_id()
                        );
                    

Bootstrap Performance Impact

WordPress 4.8 Front-end request, no plugins, twentyseventeen theme
Blackfire profile

Nextgen Bootstrap/Load (1/2)

• Goal 1 — Documentation

  - Detailed docs for old and new code

  - Include characterization tests to detect breaking changes

• Goal 2 — Modernized Flow

  - Subsystems should be cleanly swappable/extensible

• Goal 3 — Contextual Optimization

  - Only load what is effectively needed to produce the desired output

• Goal 4 — Unified Structure

  - Reduce idiosyncrasies to provide a consistent user/dev experience

• Goal 5 — Compatibility

  - Don't break existing sites

  - Grow with future requirements

Nextgen Bootstrap/Load (2/2)

• Phase 1 — Discovery

  - Be clear about the status quo

  - Identify issues

• Phase 2 — Design

  - Plan a coherent architecture that meets all requirements

  - Get rid of idiosyncrasies

• Phase 3 — Execution

  - Build with backward compatibility as requirement

  - Build with future compatibility as target

• Phase 4 — Merge Proposal

  - Ship it!

Learn — Bootstrap Documentation

• https://github.com/wp-core-bootstrap/documentation

Discuss — WordPress Slack Channel

• 1. Join make.wordpress.org Slack team:
  https://make.wordpress.org/chat/

• 2. Join the #core-bootstrap channel

Contribute — Bootstrap GitHub Organization

• https://github.com/wp-core-bootstrap