JobQueue Implementation in Swift

JobQueueCenter.swift

//MARK: -
//MARK: Private
class JobQueueCenter {
    fileprivate let storageAccessQueue = DispatchQueue(label: "com.JobQueueCenter.storageAccessQueue")
    fileprivate lazy var storage: JobQueueStorage = { ... }

    fileprivate func serializeStorage() {}
	
    fileprivate init() {
	NotificationCenter.default.addObserver(self, selector: #selector(tryPersist), name: .UIApplicationDidReceiveMemoryWarning, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(tryPersist), name: .UIApplicationWillResignActive, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(tryPersist), name: .UIApplicationDidEnterBackground, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(tryPersist), name: .UIApplicationWillTerminate, object: nil)
	    
        NotificationCenter.default.addObserver(forName: Notification.Name.JobFailedNotification, object: nil, queue: nil) { notification in
            let job = notification.object as! Job
            if job.retryableCount > 0 {
                self.enqueue(job: job)
            }
        }
    }
}



//MARK: -
//MARK: Public API
extension JobQueueCenter {
    static let current = JobQueueCenter()
	
    func enqueue(job: Job) {
        storageAccessQueue.async {
            self.storage.enqueue(job)
        }
    }
    
    func executeNext() {
        storageAccessQueue.async {
            let job = self.storage.dequeue()
            job?.run()
        }
    }
    
    func persist() {
        storageAccessQueue.async {
            self.serializeStorage()
        }
    }
}