Schedules a notification block to be submitted to a queue when the execution of a specified dispatch block has completed.
- iOS 8.0+
- macOS 10.10+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
The queue to which the supplied notification block is submitted when the observed block completes.
The notification block to submit when the observed block object completes.
This function submits the notification block immediately if execution of the observed block object has already completed.
It is not possible to be notified of multiple executions of the same block object with this interface. Instead, use the
dispatch function for that purpose.
A single dispatch block may either be observed one or more times and executed once, or it may be executed any number of times. The behavior of any other combination is undefined. Submission to a dispatch queue counts as an execution, even if cancellation using the
dispatch function means the block's code never runs.
If multiple notification blocks are scheduled for a single block object, there is no defined order in which the notification blocks are submitted to their associated queues.