From 9db09854950ed046259b508b45bd78471f33debd Mon Sep 17 00:00:00 2001
From: Uwe Steinmann <steinm@debian.org>
Date: Tue, 2 Jul 2024 16:25:05 +0200
Subject: [PATCH] isDue() reads nextrun from from database

---
 inc/inc.ClassSchedulerTask.php | 43 ++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/inc/inc.ClassSchedulerTask.php b/inc/inc.ClassSchedulerTask.php
index 5c19dda7a..2945e7861 100644
--- a/inc/inc.ClassSchedulerTask.php
+++ b/inc/inc.ClassSchedulerTask.php
@@ -259,7 +259,50 @@ class SeedDMS_SchedulerTask {
 		return $this->_params;
 	}
 
+	/**
+	 * Check if task is due
+	 *
+	 * This methods compares the current time with the time in the database
+	 * field `nextrun`.
+	 * If nextrun is smaller than the current time, the the task is due.
+	 * The methode does not rely on the value in the class variable `_nextrun`,
+	 * because that value could be 'very old', retrieved at a time
+	 * when the task list was fetched for checking due tasks e.g. by the
+	 * scheduler client. There is good reason to always take the current
+	 * value of nextrun from the database.
+	 *
+	 * Assuming there are two tasks. Task 1 takes 13 mins and task 2 takes only
+	 * 30 sec. Task 1 is run every hour and task 2 starts at 8:06. The cronjob
+	 * runs every 5 min. At e.g. 8:00 the list of tasks is read from the database
+	 * task 1 is due and starts running and before it runs it sets the database
+	 * field nextrun to 9:00. Task 2 isn't due at that time.
+	 * At 8:05 the cron job runs again, task 1 has already a new nextrun value
+	 * and will not run again. Task 2 isn't due yet and task 1 started at 8:00 is
+	 * still running.
+	 * At 8:10 task 1 is still running an not due again, but task 2 is due and
+	 * will be run. The database field `nextrun` of task 2 will be set to 8:06
+	 * on the next day.
+	 * At 8:13 task 1 which started at 8:00 is finished and the list of tasks
+	 * from that time will be processed further. Task 2 still has the old value
+	 * in the class variable `_nextrun` (8:06 the current day),
+	 * though the database field `nextrun` has been updated in
+	 * between. Taking the value of the class variable would rerun task 2 again,
+	 * though it ran at 8:10 already.
+	 * That's why this method always takes the current value of nextrun
+	 * from the database.
+	 *
+	 * @return boolean true if task is due, otherwise false
+	 */
 	public function isDue() {
+		$queryStr = "SELECT * FROM `tblSchedulerTask` WHERE `id` = " . $this->_id;
+		$resArr = $db->getResultArray($queryStr);
+		if (is_bool($resArr) && $resArr == false)
+			return false;
+		if (count($resArr) != 1)
+			return false;
+		$row = $resArr[0];
+		$this->_nextrun = $row['nextrun'];
+
 		return $this->_nextrun < date('Y-m-d H:i:s');
 	}