Ticket #34330: proof-of-concept.php

<?php

// BUG: doesn't work when multiple post meta entries exist under one key
function get_post_lock_name($id, $name) {
        return "WPPost_" . $id . "_$name";
}

function get_user_lock_name($id, $name) {
        return "WPUser_$id_$name";
}

function lock_post_meta($id, $name) {
        $lock_name = get_post_lock_name($id, $name);
        $stall = $wpdb->get_col("SELECT GET_LOCK('$lock_name', 5)");

        // TODO: check stall
}

function unlock_user_meta($id, $name) {
        global $wpdb;

        $lock_name = get_user_lock_name($id, $name);

        $result = $wpdb->get_col("SELECT RELEASE_LOCK('$lock_name')");

        // TODO: check $result
}

function unlock_post_meta($id, $name) {
        global $wpdb;

        $lock_name = get_post_lock_name($id, $name);

        $result = $wpdb->get_col("SELECT RELEASE_LOCK('$lock_name')");

        // TODO: check $result
}

function lock_user_meta($id, $name) {
        $lock_name = get_user_lock_name($id, $name);
        $stall = $wpdb->get_col("SELECT GET_LOCK('$lock_name', 5)");

        // TODO: check stall
}

function get_and_lock_user_meta($id, $name, $single) {
        global $wpdb;

        $lock_name = get_user_lock_name($id, $name);

        $stall = $wpdb->get_col("SELECT GET_LOCK('$lock_name', 5)");

        // TODO: check stall

        return get_user_meta($id, $name, $single);
}

function get_and_lock_post_meta($id, $name, $single) {
        global $wpdb;

        $lock_name = get_post_lock_name($id, $name);

        $stall = $wpdb->get_col("SELECT GET_LOCK('$lock_name', 5)");

        // TODO: check stall

        return get_post_meta($id, $name, $single);
}

function get_and_update_post_meta($id, $name, $single, $callback) {
        $value = get_and_lock_post_meta($id, $name, $single);

        $val = $callback($value);

        if (isset($val)) {
                update_post_meta($id, $name, $val);
        }

        unlock_post_meta($id, $name);
}

function get_and_update_user_meta($id, $name, $single, $callback) {
        $value = get_and_lock_post_meta($id, $name, $single);

        $val = $callback($value);

        if (isset($val)) {
                update_user_meta($id, $name, $val);
        }

        unlock_user_meta($id, $name);
}