Users: Introduce the concept of a large site to single site installations.

Currently in WordPress multisite there is a concept of large networks. The function `wp_is_large_network` is used to determine if a network has a large number of sites or users. If a network is marked as large, then 
expensive queries to calculate user counts are not run on page load but deferred to scheduled events. However there are a number of places in a single site installation where this functionality would also be useful, as 
expensive calls to count users and roles can make screens in the admin extremely slow.

In this change, the `get_user_count` function and related functionality around it is ported to be available in a single site context. This means that expensive calls to the `count_users` function are replaced with 
calls to `get_user_count`. This change also includes a new function called `wp_is_large_user_count` and a filter of the same name, to mark if a site is large.

Props johnbillion, Spacedmonkey, Mista-Flo, lumpysimon, tharsheblows, obenland, miss_jwo, jrchamp, flixos90, macbookandrew, pento, desrosj, johnjamesjacoby, jb510, davidbaumwald, costdev. 
Fixes #38741.



git-svn-id: https://develop.svn.wordpress.org/trunk@53011 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -8418,3 +8418,113 @@ function is_php_version_compatible( $required ) {
 function wp_fuzzy_number_match( $expected, $actual, $precision = 1 ) {
 	return abs( (float) $expected - (float) $actual ) <= $precision;
 }
+
+/**
+ * Returns the number of active users in your installation.
+ *
+ * Note that on a large site the count may be cached and only updated twice daily.
+ *
+ * @since MU (3.0.0)
+ * @since 4.8.0 The `$network_id` parameter has been added.
+ * @since 6.0.0 Move to wp-includes/functions.php.
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ * @return int Number of active users on the network.
+ */
+function get_user_count( $network_id = null ) {
+	if ( ! is_multisite() && null !== $network_id ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Unable to pass $network_id if not using multisite.' ), '6.0.0' );
+	}
+	return (int) get_network_option( $network_id, 'user_count', -1 );
+}
+
+/**
+ * Updates the total count of users on the site if live user counting is enabled.
+ *
+ * @since 6.0.0
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ * @return bool Whether the update was successful.
+ */
+function wp_maybe_update_user_counts( $network_id = null ) {
+	if ( ! is_multisite() && null !== $network_id ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Unable to pass $network_id if not using multisite.' ), '6.0.0' );
+	}
+
+	$is_small_network = ! wp_is_large_user_count( $network_id );
+	/** This filter is documented in wp-includes/ms-functions.php */
+	if ( ! apply_filters( 'enable_live_network_counts', $is_small_network, 'users' ) ) {
+		return false;
+	}
+
+	return wp_update_user_counts( $network_id );
+}
+
+/**
+ * Updates the total count of users on the site.
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ * @since 6.0.0
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ * @return bool Whether the update was successful.
+ */
+function wp_update_user_counts( $network_id = null ) {
+	global $wpdb;
+
+	if ( ! is_multisite() && null !== $network_id ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Unable to pass $network_id if not using multisite.' ), '6.0.0' );
+	}
+
+	$query = "SELECT COUNT(ID) as c FROM $wpdb->users";
+	if ( is_multisite() ) {
+		$query .= " WHERE spam = '0' AND deleted = '0'";
+	}
+
+	$count = $wpdb->get_var( $query );
+
+	return update_network_option( $network_id, 'user_count', $count );
+}
+
+/**
+ * Schedules a recurring recalculation of the total count of users.
+ *
+ * @since 6.0.0
+ */
+function wp_schedule_update_user_counts() {
+	if ( ! is_main_site() ) {
+		return;
+	}
+
+	if ( ! wp_next_scheduled( 'wp_update_user_counts' ) && ! wp_installing() ) {
+		wp_schedule_event( time(), 'twicedaily', 'wp_update_user_counts' );
+	}
+}
+
+/**
+ * Determines whether the site has a large number of users.
+ *
+ * The default criteria for a large site is more than 10,000 users.
+ *
+ * @since 6.0.0
+ *
+ * @param int|null $network_id ID of the network. Default is the current network.
+ * @return bool Whether the site has a large number of users.
+ */
+function wp_is_large_user_count( $network_id = null ) {
+	if ( ! is_multisite() && null !== $network_id ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Unable to pass $network_id if not using multisite.' ), '6.0.0' );
+	}
+	$count = get_user_count( $network_id );
+
+	/**
+	 * Filters whether the site is considered large, based on its number of users.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @param bool     $is_large_user_count Whether the site has a large number of users.
+	 * @param int      $count               The total number of users.
+	 * @param int|null $network_id          ID of the network. `null` represents the current network.
+	 */
+	return apply_filters( 'wp_is_large_user_count', $count > 10000, $count, $network_id );
+}