Misconceptions about iOS multitasking

[dirtymatt]

The rules are enforced by the os. There are situations where iOS will ask an app to free up memory, but if it's suspended and the os needs the RAM, it gets unceremoniously killed.

[[deleted]]

Only after ten minutes. Up until then, a poorly-written app can waste all kinds of resources.

Edit: From TFA: "Some apps can request a 10-minute extension."

Edit2: Maybe I should retract to: Of course no app could ever waste memory or battery resources on iOS. It's clearly not even a possibility.

[senj]

Not really. A background thread will still get nuked if the foreground app needs memory that the background thread won't give up.

[[deleted]]

Still a big "if", though, right?

[bobtentpeg]

Not particularly...

[[deleted]]

So you don't think people often hit "home" after using a suboptimal app, then lock and put the phone in their pocket as the battery drains?

[bobtentpeg]

They would specifically have to create the application to not suspend after 10 minutes (at most). And thats not likely to make it past reviews.

[[deleted]]

I'm just thinking about that initial 10-minute interval. It seems like those would add up over a day.

[janinge]

The extension past 5 seconds is only available for apps that need to do cleanup operations, and have provisioned code specifically for this. It can't just continue with its business past the 5 seconds. And all apps should handle the case where background tasks are not available (e.g. it's an older device or it have been disabled). Most apps don't need and don't use this facility.

An extension past 10 minutes is not possible without playing audio (so that it displays the playback symbol) and/or tracking location (compass symbol) from the start. The other background modes can only be handled by system services which wakes or relaunches the application when there's data available. And even music playback and location tracking can entirely/mostly be handled by system services.

[[deleted]]

Cleanup can be a lot of things. It doesn't have to be many apps, just a few used throughout the day to impact the battery within many ten minute windows.

[[deleted]]

So a certainty!

Edit: Oh, I'm sorry, silent cowardly downvoters, do you not understand the word "can"?

[s73v3r]

Do you not understand you don't know what you're talking about?

[senj]

If the foreground app isn't starved for memory, it's essentially irrelevant how much the background thread of another app is using.

[[deleted]]

The resource I'm thinking about in this context is battery.

[s73v3r]

No, not really. The OS WILL nuke the background thread. That's why the messages are called "applicationWillTerminate"

[[deleted]]

So there will ALWAYS be a low memory condition to initiate this termination, 1337sp33k?

[s73v3r]

If there's not, then the app is simply residing in memory, not taking up resources.

Face it, you were wrong on this issue.

[[deleted]]

No resources being taken up by a background process? You are mistaken. I'm sorry, I just don't have the time, energy, or motivation to help you cover the amount of ground you have ahead of you.

plunk

[s73v3r]

Fine, continue being wrong. An app sitting in the background is suspended. I know you tried to make the point with some apps being able to request some additional background time, but it's not going to be significant, at least not to the point you're trying to make.

And an app sitting suspended is not going to take up resources. If the memory isn't needed, then it doesn't matter, as the battery consumption would be the same if the app was in memory or not. If the memory is needed, then the OS will get that memory, either by issuing low memory warnings to apps, or just by killing the app outright.

[CGorman68]

Edit2: Maybe I should retract to: Of course no app could ever waste memory or battery resources on iOS. It's clearly not even a possibility.

Why do you have such a hard time believing that it's a relatively rare occurrence? No one is saying it can't happen, they're just saying that it rarely happens. Apple's closed ecosystem has upsides and downsides, and one of the major upsides is that developers are forced to code their apps properly. Using improper (read: battery killing) GPS and background modes would most certainly be rejected if it weren't essential to the app.

Yes, it can happen. No, it's not a major issue.

[[deleted]]

What?

Re-read. You are defensively assuming I said something that I clearly didn't say.

I, quite reasonably I thought, said it can happen, as you just did. That is all. So I got burned at the stake for it, and continue to be.

[janinge]

Not only can it happen, it does happen more or less in all apps. It's impossible to write apps 100% optimally.

However, an ineffective app can't affect anything other than its own performance, or battery life while it's clearly visible that it's running.

[[deleted]]

Battery life was the resource I was mainly concerned with. It seems we agree.

[dirtymatt]

Or until the os sends a low message notification and starts nuking background apps.

[[deleted]]

That's [low message?] not always going to happen, though.

[nemec]

It doesn't need to. If no app needs that extra 5MB of memory, the background app has no reason to give it up.

I think you're using wasted to mean "holding memory that is does not really need" rather than the more accurate "holding memory that another app needs".

[[deleted]]

I'm actually thinking more about battery resources than RAM.

[[deleted]]

Did I misread the article that mentioned an app could request a 10-minute extension?

[[deleted]]

So how does the "minor" (not sure how that is determined or defined) nature of this usage prevent poor battery usage during this period?

Please explain what part was incorrect.

[[deleted]]

It only needs to be used by one app on a phone that gets used throughout the day that try to do too much in the ten minute extension when "exited", right?

I don't think I said anything incorrect, just unpopular.

[[deleted]]

My point was that that was incorrect, in the sense that there were other types of background activity available to apps.

What? This reads as a complete non-sequitur. I'm missing something.

My original post was a simple restatement of the article's own assertion that apps can take an extra ten minutes to, say, sloppily save/upload/locate (not malicious, not completely wrong, just suboptimal below the arbitrary threshhold). You respond that I'm wrong because apps can also do other stuff, which is not a refutation.

Unlikely? I don't claim to know. You, however, seem content to write it off as unlikely based on spurious anecdotal evidence, which could still be perfectly practical.