[Macworld]

Post your comments for How iOS multitasking really works here

[linkman]

"You do not have to manage background tasks on iOS"

I disagree. This means you'll never have to kill them off manually or restart an iOS device. So what happens when you do get that battery-killing runaway app?

"apps either goes berserk or will not Suspend itself properly"
"well-written apps in the above categories"
"App Store review is never a perfect catch-all"

Since all applications aren't well-written and apparently some good ones have elevated background categories, it's inevitable that one will someday suck down a lot of battery juice. I've had it happen on iOS 3 with several Apple apps -- Safari and Music. Also, if you leave apps such as Skype,Mail, and GPS-related ones running they'll consume CPU time (and hence battery) even though they might not be needed at that time. These are prime candidates for a user to close.

[QCassidy352]

There are definitely times when background apps are sucking battery. It's probably because they're not working properly, but it does happen. My iphone will even get hot to the touch on the back, and the battery will drain very very quickly. Killing all open apps fixes this. So I don't know that I agree that you don't have to manually manage apps. You SHOULDN'T have to, but that's not the same thing.

[MrEnglish]

It's been extremely rare that I have to close out apps in the bar. Most of the time I don't even pay attention to what is in the bar unless I'm suspecting that performance is affected by an unknown source, then everything gets the close action. Under normal circumstances, it's a set it and forget it but it's not 100% that you never have to manage the apps. It is, however, a strong percent of the time. Either way, this is a good write up with more accuracy than the pundits that abound.

[rmossman]

linkman, on 04 January 2012 - 10:07 AM, said:

Since all applications aren't well-written and apparently some good ones have elevated background categories, it's inevitable that one will someday suck down a lot of battery juice. I've had it happen on iOS 3 with several Apple apps -- Safari and Music. Also, if you leave apps such as Skype,Mail, and GPS-related ones running they'll consume CPU time (and hence battery) even though they might not be needed at that time. These are prime candidates for a user to close.

I think the author's point is that the normal consumer doesn't need to know or worry about CPU, Memory, or even battery usage (outside of normal good sense situations) and we (the more knowledgeable) shouldn't go around try to show off our superior intellect by unnecessarily scaring or confusing them.

He also said that those of us who need and use GPS, Skype, etc. apps understand (or, at least, allow for) those apps use of battery, etc. Also, after years with my iPhone and iPad, I've pretty well given up on thinking about CPU or Memory usage. They've never seemed to be an issue with any app I've used at any time.

Another thing is that I think apps that have problems giving up memory, etc. correctly will quickly be spotlighted by the users and fixed by the developer.

Basically, everything you read in this article are situations and solutions that have been around in any UNIX-based system for about 30 years. I assume that OSX and iOS would have the same solutions.

[AndreaGuerra]

So, if there aren't apps in the multitasking bar, you are absolutely sure that the battery is safe...is it correct?
we can't recognize which apps are running on iOS because there isn't a management tool for manage ios'
Multitasking

[TylerL]

When a foreground app needs to allocate more memory, doing so with truly-free memory available is leaps and bounds faster than waiting for iOS to kill inactive apps to reclaim more memory.

That's why I occasionally kill known memory-hog apps if I'm going to be playing a game or anything else that warrants smooth operation.

Yes, iOS manages RAM by itself with a very nice system, but when starved of RAM flagged as Free (with no strings attached), those compromises in management can present themselves to the user as choppy performance.

[jdb8167]

linkman, on 04 January 2012 - 10:07 AM, said:

Since all applications aren't well-written and apparently some good ones have elevated background categories, it's inevitable that one will someday suck down a lot of battery juice. I've had it happen on iOS 3 with several Apple apps -- Safari and Music. Also, if you leave apps such as Skype,Mail, and GPS-related ones running they'll consume CPU time (and hence battery) even though they might not be needed at that time. These are prime candidates for a user to close.

And I think this is the reason that some Geniuses tell customers to kill everything; it is just easier than trying to isolate the app that is causing problems. It isn't very good customer service but in the end, if a customer has an iPhone that has a too fast draining battery caused by a runaway app, killing everything will solve the problem--temporarily. Probably with the further assumption that if an app is the culprit, someone will eventually isolate it, report it to Apple and it will get fixed as a long term solution. In the meantime, a customer who isn't going to understand anything that Fraser Speirs is talking about still has a solution which is better than nothing.

The downside is that it creates this myth about killing all apps to save battery and improve performance.

[soulatrium]

On my iPad 1 I often have to manually "quit" recent high-memory apps when I am about to launch an intensive game such as Infinity Blade 2. It is when I don't quit recent apps that IB2 (and other high-end games) crashes on launch. So, yes the author is right about how the recent apps bar works, but either from poor app programming or bugs in the OS, iOS often simply cannot handle itself properly when a ram-hogging app is launched if there were other high-memory apps recently in memory. The only way around this that I've found, other than restarting the device, is to manually quit apps, quite often the most recent ones that I've used.

[johnnylundy]

Excellent summary. But as with all other Apple myths, anti-Apple people will continue to parrot the same nonsense for decades. They are still saying "MAC'S (sic) are only good for graphics!"

When the iPhone first appeared, the anti-Apple nuts complained "it doesn't multitask." Now they complain that it multitasks too much. They'd complain no matter what it did.

[TheFLP]

TylerL, on 04 January 2012 - 11:20 AM, said:

Yes, iOS manages RAM by itself with a very nice system, but when starved of RAM flagged as Free (with no strings attached), those compromises in management can present themselves to the user as choppy performance.

Or, in the case of Spotify on my iPad 1, it results in iOS shutting down the app while it's in the foreground. As in, the screen is not even locked.

I was plagued by these shutdowns on a daily basis. Manually quitting other apps helped, but after the iOS 5 upgrade it just wasn't enough anymore.

But here's where it gets really weird: I started running other apps in the foreground, while Spotify plays in the background. And for three months now, iOS has not shut Spotify off even once.

In other words, when Spotify is in the foreground and memory gets low, it gets shut down — but not when it's in the background. I don't know if this is a Spotify bug or a flaw in iOS's memory management.

This post has been edited by TheFLP: 04 January 2012 - 12:48 PM

[dshan]

The problem isn't the multitasking, it's the management of the multitasking bar itself. As far as I can determine it's not "a list of recently used apps", it's a list of ALL apps that have ever been launched on the device. It seems to grow to as many apps as you have installed on your device (and some people have hundreds of apps installed) if not manually cleaned out every now and then. Apple really should limit it to the five or ten mostly recently used apps (or make it's max size a user-specified setting).

According to a post I saw some months back, by David Pogue in his NYT blog as I recall, an Apple Genius told him that when the multitasking list gets big enough, say dozens or scores of entries in size, the CPU overhead of iOS having to constantly scan and maintain it can significantly shorten your battery life. Pogue claimed that there was a very noticeable improvement in battery life when this list was cleaned out on an iPhone with a very large list of apps in its multitasking bar.

[LelandHendrix]

TheFLP, on 04 January 2012 - 12:47 PM, said:

TylerL, on 04 January 2012 - 11:20 AM, said:

Yes, iOS manages RAM by itself with a very nice system, but when starved of RAM flagged as Free (with no strings attached), those compromises in management can present themselves to the user as choppy performance.

Or, in the case of Spotify on my iPad 1, it results in iOS shutting down the app while it's in the foreground. As in, the screen is not even locked.

I was plagued by these shutdowns on a daily basis. Manually quitting other apps helped, but after the iOS 5 upgrade it just wasn't enough anymore.

But here's where it gets really weird: I started running other apps in the foreground, while Spotify plays in the background. And for three months now, iOS has not shut Spotify off even once.

In other words, when Spotify is in the foreground and memory gets low, it gets shut down — but not when it's in the background. I don't know if this is a Spotify bug or a flaw in iOS's memory management.

It's technically a Spotify bug, but it's actually a result of the fact Spotify demands more resources when in the foreground than it does in the background. In the background, only a small subset of the Spotify app is running--only the minimum part required to keep an audio stream flowing.

[dshan]

dshan, on 04 January 2012 - 12:58 PM, said:

According to a post I saw some months back, by David Pogue in his NYT blog as I recall, an Apple Genius told him that when the multitasking list gets big enough, say dozens or scores of entries in size, the CPU overhead of iOS having to constantly scan and maintain it can significantly shorten your battery life. Pogue claimed that there was a very noticeable improvement in battery life when this list was cleaned out on an iPhone with a very large list of apps in its multitasking bar.

My apologies, now that I've gone back and looked at the Pogue post I see that my memory of it was incorrect. It seems that the iPhone in question had several other settings modified in addition to the multitasking app list to produce the improved battery life, so it's not clear that the list of previously used apps was really significant. (Though it is still odd the way it seems to grow beyond what could reasonably be described as a "recently used" list...)