wordpress source code analysis(2)

In the previous chapter, we know wp-settings.php is a complex file. This file loads almost everything like plugins and active theme. We will look into it further.

After including plugin functions such as add_filter, add_actions from wp-includes/plugin.php, it loads wp-includes/default-filters.php to add a lot of predefined filters and actions. After that, it can stop loading other stuff if we just want the basics. Otherwise, it continues to load a bunch of other files, load must use plugins. Then do the first action do_action( 'muplugins_loaded' ).

The core part of do_action function is :

do {
  foreach ( (array) current($wp_filter[$tag]) as $the_ )
  if ( !is_null($the_['function']) )
  call_user_func_array($the_['function'], array_slice($args, 0, (int) $the_['accepted_args']));
} while ( next($wp_filter[$tag]) !== false );

The actions(functions) asscociated with the tag are stored in the array of array $wp_filter[$tag]. The loop calls all those functions with the parameter args.

Note that $wp_filter[$tag] is a two-dimension array. The first dimension is proirity and the second dimension is function name. The outer loop iterates over the proirities and the inner loop iterates over the functions.

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