dispatch_source_create(3) on macOS

The text 24ac40ede6c4, as macOS 10.13.6, macOS 10.13.5, macOS 10.13.4, macOS 10.13.3, macOS 10.13.2, macOS 10.13.1, macOS 10.13 shipped it.

dispatch event sources

dispatch_source_create(3) on macOS now