Resumable scheduled tasks

administrator/components/com_scheduler/src/Scheduler/Scheduler.php

@@ -39,10 +39,11 @@
 class Scheduler
 {
 	private const LOG_TEXT = [
-		Status::OK         => 'COM_SCHEDULER_SCHEDULER_TASK_COMPLETE',
-		Status::NO_LOCK    => 'COM_SCHEDULER_SCHEDULER_TASK_LOCKED',
-		Status::NO_RUN     => 'COM_SCHEDULER_SCHEDULER_TASK_UNLOCKED',
-		Status::NO_ROUTINE => 'COM_SCHEDULER_SCHEDULER_TASK_ROUTINE_NA',
+		Status::OK          => 'COM_SCHEDULER_SCHEDULER_TASK_COMPLETE',
+		Status::WILL_RESUME => 'COM_SCHEDULER_SCHEDULER_TASK_WILL_RESUME',
+		Status::NO_LOCK     => 'COM_SCHEDULER_SCHEDULER_TASK_LOCKED',
+		Status::NO_RUN      => 'COM_SCHEDULER_SCHEDULER_TASK_UNLOCKED',
+		Status::NO_ROUTINE  => 'COM_SCHEDULER_SCHEDULER_TASK_ROUTINE_NA',
 	];
 
 	/**
@@ -158,7 +159,7 @@ public function runTask(array $options): ?Task
 
 		if (\array_key_exists($exitCode, self::LOG_TEXT))
 		{
-			$level = $exitCode === Status::OK ? 'info' : 'warning';
+			$level = in_array($exitCode, [Status::OK, Status::WILL_RESUME]) ? 'info' : 'warning';
 			$task->log(Text::sprintf(self::LOG_TEXT[$exitCode], $taskId, $duration, $netDuration), $level);
 
 			return $task;

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

@@ -67,6 +67,19 @@ abstract class Status
 	 */
 	public const KNOCKOUT = 5;
 
+	/**
+	 * Exit code used when a task needs to resume (reschedule it to run a.s.a.p.).
+	 *
+	 * Use this for long running tasks, e.g. batch processing of hundreds or thousands of files,
+	 * sending newsletters with thousands of subscribers etc. These are tasks which might run out of
+	 * memory and/or hit a time limit when lazy scheduling or web triggering of tasks is being used.
+	 * Split them in smaller batches which return Status::WILL_RESUME. When the last batch is
+	 * executed return Status::OK.
+	 *
+	 * @since 4.1.0
+	 */
+	public const WILL_RESUME = 123;
+
 	/**
 	 * Exit code used when a task times out.
 	 *

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

@@ -12,6 +12,7 @@
 // Restrict direct access
 \defined('_JEXEC') or die;
 
+use DateInterval;
 use Joomla\CMS\Application\CMSApplication;
 use Joomla\CMS\Component\ComponentHelper;
 use Joomla\CMS\Event\AbstractEvent;
@@ -116,9 +117,10 @@ class Task implements LoggerAwareInterface
 	 * @since  4.1.0
 	 */
 	protected const EVENTS_MAP = [
-		Status::OK         => 'onTaskExecuteSuccess',
-		Status::NO_ROUTINE => 'onTaskRoutineNotFound',
-		'NA'               => 'onTaskExecuteFailure',
+		Status::OK          => 'onTaskExecuteSuccess',
+		Status::NO_ROUTINE  => 'onTaskRoutineNotFound',
+		Status::WILL_RESUME => 'onTaskRoutineWillResume',
+		'NA'                => 'onTaskExecuteFailure',
 	];
 
 	/**
@@ -246,11 +248,29 @@ public function run(): bool
 		// @todo make the ExecRuleHelper usage less ugly, perhaps it should be composed into Task
 		// Update object state.
 		$this->set('last_execution', Factory::getDate('@' . (int) $this->snapshot['taskStart'])->toSql());
-		$this->set('next_execution', (new ExecRuleHelper($this->taskRegistry->toObject()))->nextExec());
 		$this->set('last_exit_code', $this->snapshot['status']);
-		$this->set('times_executed', $this->get('times_executed') + 1);
 
-		if ($this->snapshot['status'] !== Status::OK)
+		if ($this->snapshot['status'] !== Status::WILL_RESUME)
+		{
+			$this->set('next_execution', (new ExecRuleHelper($this->taskRegistry->toObject()))->nextExec());
+			$this->set('times_executed', $this->get('times_executed') + 1);
+		}
+		else
+		{
+			/**
+			 * Resumable tasks need special handling.
+			 *
+			 * The are rescheduled as soon as possible to let their next step to be executed without
+			 * a very large temporal gap to the previous step.
+			 *
+			 * Moreover, the times executed does NOT increase for each step. It will increase once,
+			 * after the last step, when they return Status::OK.
+			 */
+			$this->set('next_execution', Factory::getDate('now', 'UTC')->sub(new DateInterval('PT1M'))->toSql());
+		}
+
+		// The only acceptable "successful" statuses are either clean exit or resuming execution.
+		if (!in_array($this->snapshot['status'], [Status::WILL_RESUME, Status::OK]))
 		{
 			$this->set('times_failed', $this->get('times_failed') + 1);
 		}
@@ -302,7 +322,7 @@ public function acquireLock(): bool
 		$now   = Factory::getDate('now', 'GMT');
 
 		$timeout          = ComponentHelper::getParams('com_scheduler')->get('timeout', 300);
-		$timeout          = new \DateInterval(sprintf('PT%dS', $timeout));
+		$timeout          = new DateInterval(sprintf('PT%dS', $timeout));
 		$timeoutThreshold = (clone $now)->sub($timeout)->toSql();
 		$now              = $now->toSql();
 
@@ -391,7 +411,7 @@ public function releaseLock(bool $update = true): bool
 				->bind(':times_executed', $timesExecuted)
 				->bind(':times_failed', $timesFailed);
 
-			if ($exitCode !== Status::OK)
+			if (!in_array($exitCode, [Status::OK, Status::WILL_RESUME]))
 			{
 				$query->set('times_failed = t.times_failed + 1');
 			}
@@ -495,7 +515,7 @@ protected function dispatchExitEvent(): void
 	 */
 	public function isSuccess(): bool
 	{
-		return ($this->snapshot['status'] ?? null) === Status::OK;
+		return in_array(($this->snapshot['status'] ?? null), [Status::OK, Status::WILL_RESUME]);
 	}
 
 	/**

administrator/language/en-GB/com_scheduler.ini

@@ -109,6 +109,7 @@ COM_SCHEDULER_SCHEDULER_TASK_ROUTINE_NA="Task#%1$02d has no corresponding plugin
 COM_SCHEDULER_SCHEDULER_TASK_START="Running task#%1$02d '%2$s'."
 COM_SCHEDULER_SCHEDULER_TASK_UNKNOWN_EXIT="Task#%1$02d exited with code %4$d in %2$.2f (net %3$.2f) seconds."
 COM_SCHEDULER_SCHEDULER_TASK_UNLOCKED="Task#%1$02d was unlocked."
+COM_SCHEDULER_SCHEDULER_TASK_WILL_RESUME="Task#%1$02d needs to perform more work."
 COM_SCHEDULER_SELECT_INTERVAL_MINUTES="- Select interval in Minutes -"
 COM_SCHEDULER_SELECT_TASK_TYPE="Select task, %s"
 COM_SCHEDULER_SELECT_TYPE="- Task Type -"

administrator/language/en-GB/plg_task_demotasks.ini

@@ -9,6 +9,10 @@ PLG_TASK_DEMO_TASKS_STRESS_MEMORY_DESC="What happens to a task when the PHP memo
 PLG_TASK_DEMO_TASKS_STRESS_MEMORY_OVERRIDE_DESC="What happens to a task when the system memory is exhausted?"
 PLG_TASK_DEMO_TASKS_STRESS_MEMORY_OVERRIDE_TITLE="Stress Memory, Override Limit"
 PLG_TASK_DEMO_TASKS_STRESS_MEMORY_TITLE="Stress Memory"
+PLG_TASK_DEMO_TASKS_RESUMABLE_TITLE="Resumable task"
+PLG_TASK_DEMO_TASKS_RESUMABLE_DESC="A simple task to demonstrate resumable task behaviour."
+PLG_TASK_DEMO_TASKS_RESUMABLE_STEPS_LABEL="Total number of steps"
+PLG_TASK_DEMO_TASKS_RESUMABLE_TIMEOUT_LABEL="Delay per step (seconds)"
 PLG_TASK_DEMO_TASKS_TASK_SLEEP_DESC="Sleep, do nothing for x seconds."
 PLG_TASK_DEMO_TASKS_TASK_SLEEP_ROUTINE_END_LOG_MESSAGE="TestTask1 return code is: %1$d. Processing Time: %2$.2f seconds"
 PLG_TASK_DEMO_TASKS_TASK_SLEEP_TITLE="Demo Task - Sleep"

libraries/src/Console/TasksRunCommand.php

@@ -58,10 +58,11 @@ protected function doExecute(InputInterface $input, OutputInterface $output): in
 		 * load the namespace when it's time to do that (why?)
 		 */
 		static $outTextMap = [
-			Status::OK         => 'Task#%1$02d \'%2$s\' processed in %3$.2f seconds.',
-			Status::NO_RUN    => '<warning>Task#%1$02d \'%2$s\' failed to run. Is it already running?</warning>',
-			Status::NO_ROUTINE => '<error>Task#%1$02d \'%2$s\' is orphaned! Visit the backend to resolve.</error>',
-			'N/A'              => '<error>Task#%1$02d \'%2$s\' exited with code %4$d in %3$.2f seconds.</error>',
+			Status::OK          => 'Task#%1$02d \'%2$s\' processed in %3$.2f seconds.',
+			Status::WILL_RESUME => '<notice>Task#%1$02d \'%2$s\' ran for %3$.2f seconds, will resume next time.</notice>',
+			Status::NO_RUN      => '<warning>Task#%1$02d \'%2$s\' failed to run. Is it already running?</warning>',
+			Status::NO_ROUTINE  => '<error>Task#%1$02d \'%2$s\' is orphaned! Visit the backend to resolve.</error>',
+			'N/A'               => '<error>Task#%1$02d \'%2$s\' exited with code %4$d in %3$.2f seconds.</error>',
 		];
 
 		$this->configureIo($input, $output);

plugins/task/demotasks/demotasks.php

@@ -13,6 +13,7 @@
 use Joomla\CMS\Plugin\CMSPlugin;
 use Joomla\Component\Scheduler\Administrator\Event\ExecuteTaskEvent;
 use Joomla\Component\Scheduler\Administrator\Task\Status;
+use Joomla\Component\Scheduler\Administrator\Task\Task;
 use Joomla\Component\Scheduler\Administrator\Traits\TaskPluginTrait;
 use Joomla\Event\SubscriberInterface;
 
@@ -44,6 +45,11 @@ class PlgTaskDemotasks extends CMSPlugin implements SubscriberInterface
 			'langConstPrefix' => 'PLG_TASK_DEMO_TASKS_STRESS_MEMORY_OVERRIDE',
 			'method'          => 'stressMemoryRemoveLimit',
 		],
+		'demoTask_r4.resumable' => [
+			'langConstPrefix' => 'PLG_TASK_DEMO_TASKS_RESUMABLE',
+			'method'          => 'resumable',
+			'form'            => 'testTaskForm',
+		],
 	];
 
 	/**
@@ -68,6 +74,60 @@ public static function getSubscribedEvents(): array
 		];
 	}
 
+	/**
+	 * Sample resumable task.
+	 *
+	 * Whether the task will resume is random. There's a 40% chance of finishing every time it runs.
+	 *
+	 * You can use this is a template to create long running tasks which can detect an impeding
+	 * timeout condition, return Status::WILL_RESUME and resume execution next time they are called.
+	 *
+	 * @param   ExecuteTaskEvent  $event  The event we are handling
+	 *
+	 * @return  integer
+	 *
+	 * @throws  Exception
+	 * @since   4.1.0
+	 */
+	private function resumable(ExecuteTaskEvent $event): int
+	{
+		/** @var Task $task */
+		$task    = $event->getArgument('subject');
+		$timeout = (int) $event->getArgument('params')->timeout ?? 1;
+
+		$lastStatus = $task->get('last_exit_code', Status::OK);
+
+		// This is how you detect if you are resuming a task or starting it afresh
+		if ($lastStatus === Status::WILL_RESUME)
+		{
+			$this->logTask(sprintf('Resuming task %d', $task->get('id')));
+		}
+		else
+		{
+			$this->logTask(sprintf('Starting new task %d', $task->get('id')));
+		}
+
+		// Sample task body; we are simply sleeping for some time.
+		$this->logTask(sprintf('Starting %ds timeout', $timeout));
+		sleep($timeout);
+		$this->logTask(sprintf('%ds timeout over!', $timeout));
+
+		// Should I resume the task in the next step (randomly decided)?
+		$willResume = random_int(0, 5) < 4;
+
+		// Log our intention to resume or not and return the appropriate exit code.
+		if ($willResume)
+		{
+			$this->logTask(sprintf('Task %d will resume', $task->get('id')));
+		}
+		else
+		{
+			$this->logTask(sprintf('Task %d is now complete', $task->get('id')));
+		}
+
+		return $willResume ? Status::WILL_RESUME : Status::OK;
+	}
+
 	/**
 	 * @param   ExecuteTaskEvent  $event  The `onExecuteTask` event.
 	 *