I'm developing a new application for the iphone.
I want to understand something - does the memory that my application uses shared with other applications?
What if an application causes memory leaks, does it effect the device performances after the user closes the application?
thanks.
At the moment, on iPhone you'll only be sharing memory with a certain few applications - MobilePhone, MobileMail, MobileMessaging, Safari, iPod and a few minor daemons.
If you're the active application and you need more memory than is free, then some of these applications (but not the most critical ones, like MobilePhone) will be terminated in order for you to continue. If you continue to use memory, you'll be terminated before the critical apps.
The amount of memory you can use depends on which device you're on and what else is going on on the device. Common advice is that as long as you stay under 30Mb, you'll be fine.
Once an application is terminated, the fact that it leaked memory (or not) is no longer an issue - the system will clean up and free it's entire address space.
Apps sometimes say that you should reboot your iPhone before running the app, clearing the RAM that critical daemons use for caching or whatever during normal use.
If you ever find yourself doing this, stop. If you ship an app with this requirement, you fail as a programmer and should be banned from programming. Why? Look up the amount of RAM a Playstation 2 has, then look at games like Gran Turismo and Grand Theft Auto.
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I'm building my app on a development device that does not have too many apps running at the same time. I'm expecting my customers to run the app with any number of other apps open. To ensure my app wont crash due to memory issues, I would like to test my app under expected operating conditions.
This poses a question - does the number of other apps visible in the double tap home button bar affects the memory usage of the device? In other words, if I open every app on the device, then start my app, am I more likely to receive memory warnings than if I have all other apps closed?
I remember hearing a WWDC presentation that mentioned that for some apps that use <8mb of memory, their memory gets written to disk while the app is minimized, not sure what this changes.
Thank you for the clarification.
does the number of other apps visible in the double tap home button
bar affects the memory usage of the device?
No. The multi-tasking bar is just a history of recent apps. Some of them may still be in memory, others not. There is no way for you to know just by looking at it.
When low on memory, iOS will terminate the most memory-hungry background apps first. If your app allocates a lot of memory in a short period of time, it can happen that iOS isn't able to reclaim memory fast enough and will terminate your app immediately.
All you can do is reduce your footprint as much as possible, and try not to allocate huge buffers in one go.
Just a quick note. I found out that having other apps open does affect real memory allocation. Profiling the app with "activity monitor" lets you see which apps are currently loaded in memory and how much they use. Assuming the device has 512mb, you have 512 - (what's open) to use, and iOS may kill some apps to free up memory for your app.
Yes I think the number of opened apps affects the way your app
receives memory warning. Closing all the apps running in the
background or restarting the device can decrease the memory warning
messages sent to your app (you can see this effect by using instruments).
Advise:
When you receive memory warning try to do the following:
- Stop timers and other periodic tasks.
- Stop any running metadata queries.
- Do not initiate any new tasks.
- Pause movie playback (except when playing back over AirPlay).
- Enter into a pause state if your app is a game.
- Throttle back OpenGL ES frame rates.
- Suspend any dispatch queues or operation queues executing non-critical code. (You can continue processing network requests and other time-sensitive background tasks while inactive.)
I've noticed that since iOS 4.0, the apps I developed started to not "exit" when the home button is pressed, but rather they stay in the "system tray" thing which pops out when you double click the system.
At around the same time, I noticed that the battery in my phone starts draining a lot faster. Then again, theoretically all the app should be using right now is only memory, because it is not currently active.
Which begs the question, has there ever been any benchmark on what causes the iPhone to drain the most batteries? Perhaps opengl calls, which use the graphics card would consume quite a bit? Or maybe just having the apps active mean there's less memory, and this causes faster battery loss (say, because the memory allocator must do more work etc)?
I am keen to know what other developers have tried to do to optimise battery usage.
its not opengl or allocations that cause the battery drain in fact the variables are saved on the hard disk when the application quit. They don't stay in memory cause this wouldn't be possible with running all apps at the same time. (see comments)
special thanks to Stephen Furlani for this guide in documentation
I think the only ones that can cause the faster drain are background processes that still accepted to be run in background like the voice over IP feature from Skype. (the features where big announced at the iOS 4 SDK preview back then). Background audio/video, network transfers like pandora etc. (I can't name all) but not every app!
And by the way, I also noticed that my battery sometimes not hold as long as possible on other days. But I can't locate which App cause that :(
Can anyone link me to a page that describes memory allocations for iPhone apps.
I have heard that you are limited to a sandbox of ~20 megs, depending on the state of the phone, but I can't find the source for this.
It depends on the device you're using. I've found that with an iPhone 3G, when the total memory your app is using goes over 10-14MB, it's vulnerable to crashing. When it hits 20MB, it will crash for sure.
As far as I know, Apple doesn't give any hard figures for the memory that you can use. It's always changing so it's hard to pin down. They recommend that you rely on memory warnings and respond to them appropriately.
iPhone 3GS has a much higher amount of memory available to apps (I've heard that it's around 4 times). Although the iPhone 3GS only has double the memory of the iPhone 3G, a lot of that memory is taken up by the OS. There's very little left for apps to run in. That's why the 3GS will allow apps to use so much more memory.
Also, there can be a lot of memory already in use by the OS. One example is when safari is keeping a lot of tabs open. This is why lots of games recommend that you restart the device if it crashes a lot.
When you're programming, keep an eye on the increase of memory (due to not properly deallocating objects) and the peak memory. This problem is more about real-world testing (on as many devices as possible) and good programming practices.
Here's an article to ready more about how to deal with memory problems:
http://akosma.com/2009/01/28/10-iphone-memory-management-tips/
This tool finds what is the maximum memory capacity of any iOS device. It also can also find at which memory level you received the Low Memory warning.
here is the link: https://github.com/Split82/iOSMemoryBudgetTest
It depends on current device state. Some native iPhone applications can run in background and waste device resources(Mail, Safari, Sms, Phone...) So, it's hard to say how much memory u will get...Ideally, your application should stay within 10-12Mb limit to successfully overcome any memory issues.
I believe it's
Memory warnings at 20MB
Application "crashes" at 30MB
I'm fairly certain I saw this in The iPhone Developer's Cookbook: Building Applications with the iPhone SDK by Erica Sadun (amazing book, btw).
Also: Duplicate -> Maximum runtime memory available in iPhone and iPod?.
I'm reading some people stating that if another (3rd party) app on someone's iPhone has been leaking memory, that this may reduce the (mystery) amount of RAM your app would otherwise have available.
This confuses me -- does not all app memory get released when the app is closed by the user? And only one app is open at a time on iPhone?
Normally, any memory that your application allocates will be freed when it exits. However, many of Apple's applications continue running after they're "closed", so memory leaks in Mail, for instance, can affect available memory.
In addition, there are apps out there that claim to free up allocated memory. They really don't do anything other than force some dirty pages out of the buffer cache, but they appear to do something, so people believe they must be doing something useful.
On a jailbroken phone - yes, third party apps can be running at the same time as yours. Running out of memory is common with people who like to have many apps running at once hence the need for task managers, killing tasks etc.
On an unhacked phone - no. Yours is the only non-apple app that is running, no others can run at the same time.
So what can you do? All you can do is try to use the minimum memory possible which you're probably already doing. Realistically you can only test with a factory, unhacked phone, unless you are going to spend hours trying to please everyone. If you think you are maybe using too much you could identify the larger allocations using the instruments tools ("Run with performance tool >" from within Xcode) and then post that chunk of code here to get ideas of how to reduce it.
You should run Instruments and then add the instrument "Memory Monitor" to see the memory use of all of the other processes on your phone. (Add with Window -> Library , then drag the Memory Monitor instrument to the instrument panel.
What I'm still trying to determine is why is iOS releasing memory from MY app, and not all of the other memory pig apps that are not currently running.
What is the best way to programmatically access the processes sorted by cpu rate on the iPhone (similar to that seen in the *nix top command)? sysctl()?
You can use Instruments to do this, open up Instruments (/Developer/Applications/Instruments) and choose iPhone -> Activity Monitor and hit record, it'll give you all the applications running and how much CPU, RAM and everything else they are running.
Obviously this isn't programatically but you only need to worry about the CPU of a single app at a time if your developing and using this you can profile the app in question very easily
I don't believe you can. Applications are sandboxed on the iPHone platform. A rule of thumb on that platform is to just worry about your own application because you can't access much outside of it.