iOS long task in background

Question

After reading several similar questions I don't find anything that fits into my problem. I have an app that analyzes CSV files (some kind of big data analyzer app). So far CSV files were small and the analysis didn't take too long. But now we need to support very large CSV files and the analysis takes 5-10 minutes. If the user closes the app, this process is paused and when the users opens the app again the process is resumed. We need that the analysis continues while the app is in the background.

After reading about different possibilities of running in background I have this:

1. Use BGTaskScheduler

I'm not sure how to do it. I've followed this official tutorial https://developer.apple.com/documentation/uikit/app_and_environment/scenes/preparing_your_ui_to_run_in_the_background/using_background_tasks_to_update_your_app?language=objc and I've implemented this in my AppDelegate method:

didFinishLaunchingWithOptions {
    ...
    BGTaskScheduler.shared.register(forTaskWithIdentifier: "com.mydomain.myapp.myproccess", using: nil) { task in
         self.scheduleAppRefresh()
         self.handleAppRefresh(task: task as! BGAppRefreshTask)
    }
    ...
}

func scheduleAppRefresh() {

   let request = BGAppRefreshTaskRequest(identifier: "com.mydomain.myapp.myproccess")
   request.earliestBeginDate = Date(timeIntervalSinceNow: 1) 
   do {
      try BGTaskScheduler.shared.submit(request)
   } catch {
      print("Could not schedule app refresh: \(error)")
   }
}

func handleAppRefresh(task: BGAppRefreshTask) {
   scheduleAppRefresh()
   // Run my task, but how??
}

• I don't know how to call the code inside one of my views (in fact one of my presenter cause I'm using VIPER) from appDelegate.
• I'm not sure if this is how it works. If I'm not wrong, this BGTaskScheduler is to schedule a task when app goes to background.

2. Use beginBackgroundTask.

My code was this:

func csvAnalysis() {
    DispatchQueue.global(qos: .userInitiated).async {
        // Task to analyze CSV
    }
}

and now is this:

func csvAnalysis() {
    DispatchQueue.global(qos: .userInitiated).async {

        self.backgroundTaskID = UIApplication.shared.beginBackgroundTask (withName: "mytask") {
         UIApplication.shared.endBackgroundTask(self.backgroundTaskID!)
         self.backgroundTaskID = UIBackgroundTaskIdentifier.invalid
        }

        // Task to analyze CSV

        UIApplication.shared.endBackgroundTask(self.backgroundTaskID!)
        self.backgroundTaskID = UIBackgroundTaskIdentifier.invalid
    }
}

But this way, the process keeps pausing after entering background and resuming after opening the app again.

So, is it possible to execute this long task while the app is in background?