activity3.swift

import Cocoa

class ActivityManager {

    var activityUpdate: NSBackgroundActivityScheduler?
    var serialize = DispatchQueue(label: "sync", qos: .background)

    func backgroundActivitiesSetup() {
        print("Setting up activity runner.")
        activityUpdate = NSBackgroundActivityScheduler(identifier: "…")
        activityUpdate?.interval = 15 // 1 * 60 // every 1 minute
        activityUpdate?.repeats = true
        activityUpdate?.schedule { completion in
            self.serialize.async {
                self.updateNewItems(completion)
            }
        }
    }

    func getNewItemsNow() {
        // The serialize queue should make sure no update new items requests overlap.
        serialize.async {
            self.updateNewItems()
        }
    }

    func updateNewItems(_ completion: NSBackgroundActivityScheduler.CompletionHandler? = nil) {
        defer { completion?(.finished) }

        print("\(Date()) Updating new items.")
        let numWorkers = 10
        let batchCount = 160
        var (items, totalItems) = (Array(0..<10), 100) // stub

        while totalItems > 0 {
            let lock = DispatchSemaphore(value: numWorkers)
            var startTime = Date()
            print("\(startTime) Update [\(items.count) of \(totalItems) items] started.")

            DispatchQueue.concurrentPerform(iterations: numWorkers) { index in
                defer { lock.signal() }
                let start = index * items.count / numWorkers
                let end = (index + 1) * items.count / numWorkers

                for _ in start ..< end {
                    let random = Int.random(in: 0 ..< items.count)
                    // work here
                    print("\(Date()) Update completed for \(items[random]).")
                }
            }

            lock.wait()

            let totalTime = DateInterval(start: startTime, end: Date()).duration
            print("\(Date()) Update [\(items.count) of \(totalItems) items] completed in \(totalTime) seconds.")

            (items, totalItems) = ([], 0) // stub
        }
    }
}

let a = ActivityManager()
DispatchQueue.global().asyncAfter(deadline: .now() + 15) {
    print("RUNNING AD HOC REQUEST")
    a.getNewItemsNow()
}
a.backgroundActivitiesSetup()
print("Waiting.")
RunLoop.current.run()