6 classes are annotated with QueueWorker in Drupal 8

AggregatorRefresh in core/modules/aggregator/src/Plugin/QueueWorker/AggregatorRefresh.php

Updates a feed's items.

CronQueueTestBrokenQueue in core/modules/system/tests/modules/cron_queue_test/src/Plugin/QueueWorker/CronQueueTestBrokenQueue.php

Plugin annotation @QueueWorker( id = "cron_queue_test_broken_queue", title = @Translation("Broken queue test"), cron = {"time" = 60} )

CronQueueTestException in core/modules/system/tests/modules/cron_queue_test/src/Plugin/QueueWorker/CronQueueTestException.php

Plugin annotation @QueueWorker( id = "cron_queue_test_exception", title = @Translation("Exception test"), cron = {"time" = 1} )

CronQueueTestRequeueException in core/modules/system/tests/modules/cron_queue_test/src/Plugin/QueueWorker/CronQueueTestRequeueException.php

Plugin annotation @QueueWorker( id = "cron_queue_test_requeue_exception", title = @Translation("RequeueException test"), cron = {"time" = 60} )

LocaleTranslation in core/modules/locale/src/Plugin/QueueWorker/LocaleTranslation.php

Executes interface translation queue tasks.

ThumbnailDownloader in core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php

Process a queue of media items to fetch their thumbnails.