# Dispatch Work Item The work you want to perform, encapsulated in a way that lets you attach a completion handle or execution dependencies. ## Discussion A dispatch work item encapsulates work to be performed on a dispatch queue or within a dispatch group. You can also use a work item as a dispatch source event, registration, or cancellation handler. ## Topics ### Creating a Work Item [`extern dispatch_block_t dispatch_block_create(dispatch_block_flags_t flags, dispatch_block_t block);`](/documentation/Dispatch/dispatch_block_create) Creates a new dispatch block on the heap using an existing block and the given flags. [`extern dispatch_block_t dispatch_block_create_with_qos_class(dispatch_block_flags_t flags, dispatch_qos_class_t qos_class, int relative_priority, dispatch_block_t block);`](/documentation/Dispatch/dispatch_block_create_with_qos_class) Creates a new dispatch block from an existing block and the given flags, and assigns it the specified quality-of-service class and relative priority. [`typedef void (^)(void) dispatch_block_t;`](/documentation/Dispatch/dispatch_block_t) The prototype of blocks submitted to dispatch queues, which take no arguments and have no return value. [`dispatch_block_flags_t`](/documentation/Dispatch/dispatch_block_flags_t) ### Scheduling Work Items [`extern void dispatch_block_perform(dispatch_block_flags_t flags, dispatch_block_t block);`](/documentation/Dispatch/dispatch_block_perform) Creates, synchronously executes, and releases a dispatch block from the specified block and flags. ### Adding a Completion Handler [`extern void dispatch_block_notify(dispatch_block_t block, dispatch_queue_t queue, dispatch_block_t notification_block);`](/documentation/Dispatch/dispatch_block_notify) Schedules a notification block to be submitted to a queue when the execution of a specified dispatch block has completed. ### Delaying Execution of a Work Item [`extern intptr_t dispatch_block_wait(dispatch_block_t block, dispatch_time_t timeout);`](/documentation/Dispatch/dispatch_block_wait) Waits synchronously until execution of the specified dispatch block has completed or until the specified timeout has elapsed. ### Canceling a Work Item [`extern void dispatch_block_cancel(dispatch_block_t block);`](/documentation/Dispatch/dispatch_block_cancel) Cancels the specified dispatch block asynchronously. [`extern intptr_t dispatch_block_testcancel(dispatch_block_t block);`](/documentation/Dispatch/dispatch_block_testcancel) Tests whether the given dispatch block has been canceled. --- 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)