Merge branch 'main' into issue-3911issue-3911

1 files changed, 99 insertions, 0 deletions

diff --git a/lib/classes/StudipLock.php b/lib/classes/StudipLock.php
new file mode 100644
index 0000000..ce5752f
--- /dev/null
+++ b/lib/classes/StudipLock.php
@@ -0,0 +1,99 @@
+<?php
+/**
+ * StudipLock.php
+ * class with methods to perform cooperative advisory locking
+ * using the GET_LOCK feature from Mysql
+ * https://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_get-lock
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * @author      André Noack <noack@data-quest.de>
+ * @copyright   2013 Stud.IP Core-Group
+ * @license     http://www.gnu.org/licenses/gpl-2.0.html GPL version 2
+ * @category    Stud.IP
+*/
+class StudipLock
+{
+    /**
+     * name of active lock
+     * @var string
+     */
+    private static $current;
+
+    /**
+     * returns the name of the current active lock
+     * @return string name of active lock
+     */
+    public static function getCurrent()
+    {
+        return self::$current;
+    }
+
+    /**
+     * Tries to obtain a lock with a name given by the string $lockname,
+     * using a timeout of $timeout seconds. Returns 1 if the lock was obtained
+     * successfully, 0 if the attempt timed out
+     * (for example, because another client has previously locked the name),
+     * or NULL if an error occurred
+     * If a name has been locked by one client, any request by another client
+     * for a lock with the same name is blocked.
+     *
+     * @param string $lockname
+     * @param number $timeout in seconds
+     * @throws UnexpectedValueException if there is already an active lock
+     * @return integer 1 if the lock was obtained successfully, 0 if the attempt timed out
+     */
+    public static function get($lockname, $timeout = 10)
+    {
+        if (self::$current !== null) {
+            throw new UnexpectedValueException(sprintf(
+                'could not acquire new lock, %s still active',
+                self::$current
+            ));
+        }
+        $ok = DBManager::get()->fetchColumn("SELECT GET_LOCK(?,?)", [self::lockname($lockname), $timeout]);
+        if ($ok) {
+            self::$current = $lockname;
+        }
+        return $ok;
+    }
+
+    /**
+     * check if lock with given name is available
+     *
+     * @param string $lockname
+     * @return integer 1 if lock is available
+     */
+    public static function isFree($lockname)
+    {
+        return DBManager::get()->fetchColumn("SELECT IS_FREE_LOCK(?)", [self::lockname($lockname)]);
+    }
+
+    /**
+     * release the current lock
+     *
+     * @return integer 1 if the lock could be released
+     */
+    public static function release()
+    {
+        if (self::$current) {
+            return DBManager::get()->fetchColumn("SELECT RELEASE_LOCK(?)", [self::lockname(self::$current)]);
+        }
+        return 0;
+    }
+
+    /**
+     * prepends the name of current database to lockname
+     * because locks are server-wide
+     *
+     * @param string $lockname
+     * @return string
+     */
+    public static function lockname($lockname)
+    {
+        return $GLOBALS['DB_STUDIP_DATABASE'] . '_' . $lockname;
+    }
+}