Enhance task locks and events

- Updates task locks (the `locked` column) so they now use a timestamp
  to allow for recovery from a fatal failure. Includes updates to SQL
  scripts.
- Dispatch a new onTaskRecoverFailure event on "recovery" from a fatal
  failure.
- Actually dispatch task exit events (oops!)
- Update the event class declaration for onExecuteTask to be more
  elegant, readable. [1]

[1]: http://#35143#discussion_r700897628 / @Denitz

administrator/components/com_admin/sql/updates/mysql/4.1.0-2021-08-08.sql

@@ -18,7 +18,7 @@ CREATE TABLE IF NOT EXISTS `#__scheduler_tasks` (
 	`next_execution` datetime COMMENT 'Timestamp of next (planned) run, referred for execution on trigger',
 	`times_executed` int DEFAULT '0' COMMENT 'Count of successful triggers',
 	`times_failed` int DEFAULT '0' COMMENT 'Count of failures',
-	`locked` tinyint NOT NULL DEFAULT 0,
+	`locked` datetime,
 	`ordering` int NOT NULL DEFAULT 0 COMMENT 'Configurable list ordering',
 	`params` text NOT NULL,
 	`note` text,

administrator/components/com_admin/sql/updates/postgresql/4.1.0-2021-08-08.sql

@@ -17,7 +17,7 @@ CREATE TABLE IF NOT EXISTS "#__scheduler_tasks"
 	"next_execution" timestamp without time zone,
 	"times_executed" int NOT NULL DEFAULT '0',
 	"times_failed" int DEFAULT '0',
-	"locked" smallint default 0 NOT NULL,
+	"locked" timestamp without time zone,
 	"ordering" bigint DEFAULT 0 NOT NULL,
 	"params" text NOT NULL,
 	"note" text DEFAULT '',

administrator/components/com_scheduler/src/Task/Task.php

@@ -16,6 +16,7 @@
 
 use Assert\Assertion;
 use Assert\AssertionFailedException;
+use DateInterval;
 use Exception;
 use Joomla\CMS\Application\CMSApplication;
 use Joomla\CMS\Event\AbstractEvent;
@@ -130,6 +131,20 @@ public function getRecord(): object
 	 */
 	public function run(): bool
 	{
+		/*
+		* Dispatch event if task lock is not released (NULL). This only happens if the task execution
+		* was interrupted by a fatal failure.
+		 * @todo add listeners. We can have Email, PushBullet, etc
+		*/
+		if ($this->get('locked') === null)
+		{
+			$event = AbstractEvent::create('onTaskRecoverFailure', [
+				'subject' => $this
+				]
+			);
+			$this->app->getDispatcher()->dispatch($event);
+		}
+
 		if (!$this->acquireLock())
 		{
 			$this->snapshot['status'] = Status::NO_LOCK;
@@ -145,7 +160,7 @@ public function run(): bool
 		$event = AbstractEvent::create(
 			'onExecuteTask',
 			[
-				'eventClass'      => 'Joomla\Component\Scheduler\Administrator\Event\ExecuteTaskEvent',
+				'eventClass'      => ExecuteTaskEvent::class,
 				'subject'         => $this,
 				'routineId'       => $this->get('type'),
 				'langConstPrefix' => $this->get('taskOption')->langConstPrefix,
@@ -185,12 +200,24 @@ public function acquireLock(): bool
 		$db = $this->db;
 		$query = $db->getQuery(true);
 		$id = $this->get('id');
+		$now = Factory::getDate('now', 'GMT');
+
+		// @todo Get timeout in seconds from component configuration
+		$timeout = new DateInterval('PT100S');
+		$timeoutThreshold = $now->sub($timeout)->toSql();
+		$now = $now->toSql();
 
 		$query->update($db->qn('#__scheduler_tasks', 't'))
-			->set('t.locked = 1')
+			->set('t.locked = :now')
 			->where($db->qn('t.id') . ' = :taskId')
-			->where($db->qn('t.locked') . ' = 0')
-			->bind(':taskId', $id, ParameterType::INTEGER);
+			->extendWhere('AND', [
+				$db->qn('t.locked') . ' < :threshold',
+				$db->qn('t.locked') . 'IS NULL'],
+				'OR'
+			)
+			->bind(':taskId', $id, ParameterType::INTEGER)
+			->bind(':now', $now)
+			->bind(':threshold', $timeoutThreshold);
 
 		try
 		{
@@ -206,7 +233,7 @@ public function acquireLock(): bool
 			return false;
 		}
 
-		$this->set('locked', 1);
+		$this->set('locked', $now);
 
 		return true;
 	}
@@ -229,9 +256,9 @@ public function releaseLock(bool $update = true): bool
 		$id = $this->get('id');
 
 		$query->update($db->qn('#__scheduler_tasks', 't'))
-			->set('t.locked = 0')
+			->set('t.locked = NULL')
 			->where($db->qn('t.id') . ' = :taskId')
-			->where($db->qn('t.locked') . ' = 1')
+			->where($db->qn('t.locked') . ' IS NOT NULL')
 			->bind(':taskId', $id, ParameterType::INTEGER);
 
 		if ($update)
@@ -275,7 +302,7 @@ public function releaseLock(bool $update = true): bool
 			return false;
 		}
 
-		$this->set('locked', 0);
+		$this->set('locked', null);
 
 		return true;
 	}
@@ -306,10 +333,11 @@ private function handleExit(bool $success = true): bool
 	{
 		$eventName = $success ? 'onTaskExecuteSuccess' : 'onTaskExecuteFailure';
 
-		AbstractEvent::create($eventName, [
+		$event = AbstractEvent::create($eventName, [
 				'subject' => $this
 			]
 		);
+		$this->app->getDispatcher()->dispatch($event);
 
 		return $success;
 	}

installation/sql/mysql/extensions.sql

@@ -906,7 +906,7 @@ CREATE TABLE IF NOT EXISTS `#__scheduler_tasks` (
   `next_execution` datetime COMMENT 'Timestamp of next (planned) run, referred for execution on trigger',
   `times_executed` int DEFAULT '0' COMMENT 'Count of successful triggers',
   `times_failed` int DEFAULT '0' COMMENT 'Count of failures',
-  `locked` tinyint NOT NULL DEFAULT 0,
+  `locked` datetime,
   `ordering` int NOT NULL DEFAULT 0 COMMENT 'Configurable list ordering',
   `params` text NOT NULL,
   `note` text,

installation/sql/postgresql/extensions.sql

@@ -869,7 +869,7 @@ CREATE TABLE IF NOT EXISTS "#__scheduler_tasks"
     "next_execution" timestamp without time zone,
     "times_executed" int NOT NULL DEFAULT '0',
     "times_failed" int DEFAULT '0',
-    "locked" smallint default 0 NOT NULL,
+    "locked" timestamp without time zone,
 	"ordering" bigint DEFAULT 0 NOT NULL,
     "params" text NOT NULL,
     "note" text DEFAULT '',