How to execute a method every second on a background thread so it doesn't affect the performance of the app

Question

I am trying to access my database every 30 seconds, however, whenever the method executes I can clearly see a performance dip in the application.

So far this is my current code:

var timer = Timer()

override func viewDidLoad() {
    super.viewDidLoad()
    scheduledTimerWithTimeInterval()

}

func scheduledTimerWithTimeInterval(){
    timer = Timer.scheduledTimer(timeInterval: 30, target: self, selector: #selector(self.updateCounting), userInfo: nil, repeats: true)
}

@objc func updateCounting(){
    getDatabaseInfo()
}

I am trying to do the same thing, except I would like to execute the getDatabaseInfo() method on a background thread so that the app's performance is not compromised.

Rob · Answer 1 · 2018-12-26T08:37:38.433

You can just run the timer directly on the background queue by using a DispatchSourceTimer:

private var timer: DispatchSourceTimer?

func startTimer() {
    let queue = DispatchQueue(label: Bundle.main.bundleIdentifier! + ".timer")
    timer = DispatchSource.makeTimerSource(queue: queue)
    timer!.schedule(deadline: .now(), repeating: .seconds(1))
    timer!.setEventHandler { [weak self] in
        // do whatever stuff you want on the background queue here here

        getDatabaseInfo()

        DispatchQueue.main.async {
            // update your model objects and/or UI here
        }
    }
    timer!.resume()
}

func stopTimer() {
    timer?.cancel()
    timer = nil
}

Using Timer, you schedule it on the main queue's run loop and then have it dispatch the task to a background queue, and then dispatch UI/model updates back to the main queue. Using dispatch timer, like above, bypasses that first step, running the timer directly on a GCD background queue.

score 5 · Accepted Answer · answered Dec 26 '18 at 06:20

5

Use Grand Central Dispatch :

DispatchQueue.global(qos: .background).async {
    getDatabaseInfo()
}

answered Dec 26 '18 at 06:20

ielyamani

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3

Worth mentioning that any UI updates necessary after getting database info should then be run inside a `main` thread, as in Nikx's answer. – Serdnad Dec 26 '18 at 08:02

score 2 · Answer 3 · edited Dec 26 '18 at 07:13

You can try with below code.

var timer = Timer()

override func viewDidLoad() {
    super.viewDidLoad()
    scheduledTimerWithTimeInterval()

}

func scheduledTimerWithTimeInterval(){
    timer = Timer.scheduledTimer(timeInterval: 30, target: self, selector: #selector(self.updateCounting), userInfo: nil, repeats: true)
}

@objc func updateCounting(){

    DispatchQueue.global(qos: .background).async {
        print("This is run on the background queue")
        getDatabaseInfo()
        DispatchQueue.main.async {
            print("This is run on the main queue, after the previous code in outer block")
        }
    }
}

I guess, the `qos` parameter should be **User Interactive** or **User Initiated** and not _background_ as it is of least priority . You can refer to the following : [QOS Parameters DispatchQueue](https://www.allaboutswift.com/dev/2016/5/21/gcd-with-qos-in-swift) — Shubham Bakshi, Dec 26 '18 at 06:31

How to execute a method every second on a background thread so it doesn't affect the performance of the app

3 Answers3

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