switch_to_blog( int $new_blog, bool $deprecated = null )

function switch_to_blog( $new_blog, $deprecated = null ) {
	global $wpdb;

	$blog_id = get_current_blog_id();
	if ( empty( $new_blog ) ) {
		$new_blog = $blog_id;
	}

	$GLOBALS['_wp_switched_stack'][] = $blog_id;

	/*
	 * If we're switching to the same blog id that we're on,
	 * set the right vars, do the associated actions, but skip
	 * the extra unnecessary work
	 */
	if ( $new_blog == $blog_id ) {
		/**
		 * Fires when the blog is switched.
		 *
		 * @since WP-MU (3.0.0)
		 *
		 * @param int $new_blog New blog ID.
		 * @param int $new_blog Blog ID.
		 */
		do_action( 'switch_blog', $new_blog, $new_blog );
		$GLOBALS['switched'] = true;
		return true;
	}

	$wpdb->set_blog_id( $new_blog );
	$GLOBALS['table_prefix'] = $wpdb->get_blog_prefix();
	$prev_blog_id = $blog_id;
	$GLOBALS['blog_id'] = $new_blog;

	if ( function_exists( 'wp_cache_switch_to_blog' ) ) {
		wp_cache_switch_to_blog( $new_blog );
	} else {
		global $wp_object_cache;

		if ( is_object( $wp_object_cache ) && isset( $wp_object_cache->global_groups ) ) {
			$global_groups = $wp_object_cache->global_groups;
		} else {
			$global_groups = false;
		}
		wp_cache_init();

		if ( function_exists( 'wp_cache_add_global_groups' ) ) {
			if ( is_array( $global_groups ) ) {
				wp_cache_add_global_groups( $global_groups );
			} else {
				wp_cache_add_global_groups( array( 'users', 'userlogins', 'usermeta', 'user_meta', 'useremail', 'userslugs', 'site-transient', 'site-options', 'blog-lookup', 'blog-details', 'rss', 'global-posts', 'blog-id-cache', 'networks', 'sites', 'site-details' ) );
			}
			wp_cache_add_non_persistent_groups( array( 'counts', 'plugins' ) );
		}
	}

	/** This filter is documented in wp-includes/ms-blogs.php */
	do_action( 'switch_blog', $new_blog, $prev_blog_id );
	$GLOBALS['switched'] = true;

	return true;
}