feat(BackgroundJobs): Allow preventing parallel runs for a job class

Signed-off-by: Marcel Klehr <mklehr@gmx.net>

lib/private/BackgroundJob/JobList.php

@@ -35,6 +35,7 @@ use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\AutoloadNotAllowedException;
 use OCP\BackgroundJob\IJob;
 use OCP\BackgroundJob\IJobList;
+use OCP\DB\Exception;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\IConfig;
 use OCP\IDBConnection;
@@ -382,4 +383,21 @@ class JobList implements IJobList {
 			->where($query->expr()->eq('id', $query->createNamedParameter($job->getId()), IQueryBuilder::PARAM_INT));
 		$query->executeStatement();
 	}
+
+	public function hasReservedJob(?string $className): bool {
+		$query = $this->connection->getQueryBuilder();
+		$query->select('*')
+			->from('jobs')
+			->where($query->expr()->neq('reserved_at', $query->createNamedParameter(0, IQueryBuilder::PARAM_INT)));
+
+		if ($className !== null) {
+			$query->andWhere($query->expr()->eq('class', $query->createNamedParameter($className)));
+		}
+
+		try {
+			return $query->executeQuery()->rowCount() > 0;
+		} catch (Exception $e) {
+			return false;
+		}
+	}
 }

lib/public/BackgroundJob/IJobList.php

@@ -145,4 +145,13 @@ interface IJobList {
 	 * @since 23.0.0
 	 */
 	public function resetBackgroundJob(IJob $job): void;
+
+	/**
+	 * Checks whether a job of the passed class is reserved to run
+	 *
+	 * @param string|null $className
+	 * @return bool
+	 * @since 27.0.0
+	 */
+	public function hasReservedJob(?string $className): bool;
 }

lib/public/BackgroundJob/Job.php

@@ -43,6 +43,7 @@ abstract class Job implements IJob {
 	protected int $lastRun = 0;
 	protected $argument;
 	protected ITimeFactory $time;
+	protected bool $allowParallelRuns = true;
 
 	/**
 	 * @since 15.0.0
@@ -72,6 +73,11 @@ abstract class Job implements IJob {
 		$jobList->setLastRun($this);
 		$logger = \OCP\Server::get(LoggerInterface::class);
 
+		if (!$this->getAllowParallelRuns() && $jobList->hasReservedJob(get_class($this))) {
+			$logger->debug('Skipping ' . get_class($this) . ' job with ID ' . $this->getId() . ' because another job with the same class is already running', ['app' => 'cron']);
+			return;
+		}
+
 		try {
 			$jobStartTime = $this->time->getTime();
 			$logger->debug('Run ' . get_class($this) . ' job with ID ' . $this->getId(), ['app' => 'cron']);
@@ -132,6 +138,25 @@ abstract class Job implements IJob {
 		return $this->argument;
 	}
 
+	/**
+	 * Set this to false to prevent two Jobs from this class from running in parallel
+	 *
+	 * @param bool $allow
+	 * @return void
+	 * @since 27.0.0
+	 */
+	public function setAllowParallelRuns(bool $allow) {
+		$this->allowParallelRuns = $allow;
+	}
+
+	/**
+	 * @return bool
+	 * @since 27.0.0
+	 */
+	public function getAllowParallelRuns(): bool {
+		return $this->allowParallelRuns;
+	}
+
 	/**
 	 * The actual function that is called to run the job
 	 *