activity.swift

var activity: NSBackgroundActivityScheduler?

func runActivity() {
    activity = NSBackgroundActivityScheduler(identifier: "lkasjdlaksjdaslkjd")
    activity?.repeats = true
    activity?.interval = 15
    activity?.schedule { completion in
                        
        // This doesn't make sense: defer should be periodically checked in
        // the middle of a long job.
        if let activity = self.activity, activity.shouldDefer {
            completion(.deferred)
            return
        }

        // Running a bunch of concurrent stuff is fine, but hard to manage
        // if you're worried about needing to defer.
        let numWorkers = 10
        let lock = DispatchSemaphore(value: numWorkers)
        let date = Date()
        DispatchQueue.concurrentPerform(iterations: numWorkers) { (index) in
            defer { lock.signal() }
            print("activity [\(date)] - \(index)")
        }
        lock.wait()
        print("done")
        completion(.finished)
    }
}