# barrier Cause the work item to act as a barrier block when submitted to a concurrent queue. ``` static let barrier: DispatchWorkItemFlags ``` ## Discussion When submitted to a concurrent queue, a work item with this flag acts as a barrier. Work items submitted prior to the barrier execute to completion, at which point the barrier work item executes. Once the barrier work item finishes, the queue returns to scheduling work items that were submitted after the barrier. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)