As I understand it, on iOS third part apps don’t actually do any tasks in the background, most such services are actually implemented by platform services provided by Apple that the third part apps request or subscribe to. So for example apps request an Apple service to do a background download on their behalf. Or the app subscribes to a notification feed that wakes it up when triggered to handle the notification, but the app doesn't do a download or wait for notifications itself.

Very often on iOS when you see a notification 'from an app' or something in the background is completed 'by an app', in fact the app didn't do any of it. This means fine grained permissions for background processing aren't really an issue on iOS, because such behavior is managed and guaranteed by Apple. It only matters when there's a security or privacy implication.

This is why background activities came so much later to iOS, because Apple had to very carefully think through and implement all the background services apps would require in an efficient and secure way.

EDIT: To be clear there are some exceptions but I'm not sure exactly what they are.

For some basic use cases, like notifications and downloads, there is a special system or api that allows your app to do that in the background without actually running.

If you want to play audio or track gps in the background you need to do things yourself though.

OK, hence the Facebook issue where they played a silent audio track to keep their app active. I'd forgotten about that, thanks.

Wow, that sucks is again super user hostile, I'm so happy I removed their app.

Technically, you could have an app that plays silent audio in the background to keep from getting killed and then do something else, but that would get flagged by the review process.

But, if I recall correctly, VLC will continue a background file transfer session from its built in web server on iOS if you play a movie in the background. Otherwise it will be killed after 10 minutes.

I think they've wisened up to that trick. My girlfriend and I use a guided meditation app that has long silences in the audio. If the screen is off, her phone kills the app after about thirty seconds of silence, making the app practically useless.

I was going to report a bug to the app suggesting they include some ultrasonic or subsonic audio to defeat this mechanism, but it's just an arms race at that point. The phone will start looking at the total power in the audible spectrum to decide whether to kill the app or something.

This kind of thing is infuriating and prevents apps from doing anything outside of the box, stifling innovation and making users frustrated.

>I don’t think you could implement a tracking socket masquerading as a background download

The Facebook app used to play a silent audio track to stay active in the background, until they got called out: https://www.reddit.com/r/iphone/comments/3opxhm/facebook_app...

Holy crap, I didn’t know that. Yet another reason I was right to uninstall the app and just use the website.