I'm developing an RSS reader type iPhone application and it is nearing completion, however I upgraded to Xcode 4 with iOS 4.3 yesterday and I have run into some serious memory issues. My App now frequently gets memory warnings, I'm handling didReceiveMemoryWarning, and releasing all my cached images etc, but this does not provide a good user experience. I've also been using Instruments in an attempt to diagnose the problem, but this has been bringing up more questions then answers.
• Does the SDK 4.3 use more memory ? I wasn't receiving memory warnings before I upgraded. Not sure if this is relevant or not, but I'm doing most of my testing on an iPhone 3G with iOS 4.2 on it (4.3 is not supported on a 3G).
• Why does the allocations instrument tool live bytes column not match the real memory column in the activity monitor tool ? The activity monitor tool always reports more memory usage.
• According to leaks my app does not leak memory, in the simulator or on an actual iPhone, but when I look at allocations, it seems that as I transition between views and then pop views, the live bytes column does not return to its previous value, which is consistent with leaking memory ? (Yes subviews are released after they are popped)
• My app frequently reports a memory warning on startup, but only when I'm profiling the application with leaks. Does leaks cause extra memory overhead ?
• Perhaps this is a difficult question to answer, but what is a reasonable memory footprint for an iPhone app ? When I'm running leaks, my app will almost certainly be killed due to low memory a few minutes into being run, but allocations in the leaks tool reports I'm using less then 2 MB when the app is terminated.
• Why does the activity monitor instrument have a column for virtual memory ? Everything I've read states that the iPhone does not utilize virtual memory ?
The 4.3 SDK probably does use more memory, but if that's a question you're asking then you're probably on the wrong track, because as a developer that should not factor into how stable your app is.
I would not worry about the discrepancy between what Allocations reports and what Activity Monitor reports. It is also not unusual for the memory footprint to grow, as views are pushed and popped, and not shrink. Another answer on how free(3) works explains this phenomenon in better detail.
A reasonable memory footprint for an iOS app is the lowest amount your app needs in order to function.
iOS does indeed use virtual memory. From Apple's Memory Usage Performance Guidelines / About the Virtual Memory System:
Both Mac OS X and iOS include a fully-integrated virtual memory system that you cannot turn off; it is always on. Both system also provide up to 4 gigabytes of addressable space per 32-bit process.
...
Although Mac OS X supports a backing store, iOS does not. In iPhone applications, read-only data that is already on the disk (such as code pages) is simply removed from memory and reloaded from disk as needed. Writable data is never removed from memory by the operating system. Instead, if the amount of free memory drops below a certain threshold, the system asks the running applications to free up memory voluntarily to make room for new data. Applications that fail to free up enough memory are terminated.
I recommend you read through the whole document, especially Finding Memory Leaks. You can also use the Build-and-Analyze feature, which uses the built-in Clang to statically detect several kinds of bugs, including memory leaks.
Related
I am working on a mail client on iPad (similar to that of the default app client) and using core data framework as a cache to increase performance . My app uses around 4.5 - 5 MB of heap memory and then it crashes because of memory overflow (detected this using allocation instrument). If I try to reduce memory my performance becomes very slow and sluggish because I am not able to cache my views, data structure (which store folders and all the mails) and tableviews.
I have checked my crashLogs and I see jettisoned written in front of my App which confirms that OS has forcefully closed my App!
I have used instrument to detect these limits. Please find the attached image here
This is a snapshot my recordings just before the app crashes.
I have tested my app on simulator and it stabilizes itself at 6 - 7 MB of heap memory.
Is there any way so that I can ask OS for more memory or avoid crash with a little redesign in my code.
Any suggestions or help would be highly appreciated.
6-8MB of memory should never be a problem. Likely you are either trashing memory or if you are running a debug version and have Zombies turned on, the default is to never delete the zombies. NSZombiesEnabled=YES and NSDeallocateZombies=NO will appear to leak memory as nothing is ever deleted.
how do i increase the available memory (more concrete: the part of the RAM) that can be used by my app?
i am not referring to the space available on the harddisk of an iphone, but to the RAM.
does anyone know if there's a way to use the whole free part of the RAM for my app only?
i have to clear this up a bit, sorry if it was too vague:
i had to think of the java heap size, which can be increased by adding a parameter to the startup command of the java programming.
as i don't know, but at the moment suppose on the iphone something similar happens (every app has just xxMB RAM for execution) this value might be adjustable, so that i can use the whole remaining RAM for my app.
which pretty much is what i need for this special app (non-app-store-publication; file-sizes between 50MB and several 100MB)
How do i increase the available memory?
Short answer: you don't.
Memory is managed by the kernel.
Your application process can't control this.
You can't explicitly control this - this is managed by iOS.
You can't do that. Try reducing your memory usage instead of looking for ways to remove well needed limits.
Store your data instead and read from it when needed.
I don't know for sure if you can configure RAM allocated for your app. I think that is taken care of by the iOS kernel
It's unlikely (read: not going to work) that you will be able to allocate anything more than a few Mb in your application at once.
Not planning on publishing your app to the App Store won't change this. Apple don't officially acknowledge the amount of memory in iOS devices. But its known that devices have between 128Mb and 512Mb of physical RAM.
With the kernel, essential applications (Phone app, etc), background processes, etc, you won't have anything like that available to your application. Careful analysis in instruments would suggest that you'll generally start getting memory warnings when you've allocated around 22Mb of RAM in your application.
A change made in iOS 5 makes the watchdog process much more aggressive with killing applications after you get a memory warning. If you get a memory warning on iOS5 you have to reduce your memory usage or you will get jettisoned by the OS.
If you want to proceed, you will have to figure out how to reduce the amount of memory your datasets require. Its unlikely that all of the 100Mb file needs to be in memory at once. iOS devices have "relatively" fast CPU's and storage, you'll have to architect your application to read and write to storage in chunks and work on smaller subsets of your data.
Some related Stackoverflow questions and links:
Monitor memory usage in an iphone app?
How much memory can an iPhone app use?
10 iPhone Memory Management Tips
I wrote an app compiled against ios 3 that would easily allocate up to 100 mb of memory for image processing purposes. However, when that same app was compiled against the ios 4 sdk, I found that it crashed when many apps were open in the background. When I kill the background apps, the application then runs fine. I reduced the memory usage to 70mb, and I still find that it crashes when many background apps are open.
Why are apps compiled against ios 3 are able to get more memory on phones running ios 4?? Is there something special you need to do to tell the ios 4 OS to give you more memory? Is there a way to cause background apps to be closed in order to allocate more memory for your app?
BTW, the app uses Core Graphics to some extent. Would that affect the apps ability to request memory?
Given your description, your app was pushing the memory allocation envelope on iOS 3.x, but goes too far in 4.x, likely because the newer operating system is using more memory.
The only solution is to use less memory. It really is that simple. You can't control how much memory the underlying OS will use to run processes. The only thing you can control is your app and how much memory you allocate so you don't crash.
It's unlikely that you "find that it crashes when many background apps are open". Almost certainly the system is terminating your app for using too much memory and ignoring any warnings to that effect. (I guess you could crash by trying to allocate more memory than the system has available, but that would have to be a very large allocation made in a large chunk).
Tell us more about how you're allocating this memory. Are you paying attention to low memory warnings?
How much real memory should my iphone app be using? What's going too high?
Keeping an eye on -(void)applicationDidReceiveMemoryWarning:(UIApplication *)application is definitely important, but if this is game, chances are the assets (notably textures presently on screen) can't simply be deallocated when that warning is received.
If you're a bit on the high side (20 MB +) I would recommend doing a bit of testing. Using Instruments and the Object Allocation tool (Run > Run with Performance Tool > Object Allocations) you can monitor how large your memory footprint gets. Then, try running Safari and fill the pages, then a few games and whatever else you can to get the memory higher, and see how your app performs.
In my testing for a recent release, 24 MB seemed to be pretty safe, and is a number I've heard elsewhere. Once you get above 30 or so MB, chances are your users will start having rare crashes (which happens to be the case for us, verified by crash reports). The higher you go, the more crashes users will see. There's no specific limit though, for the sake of testing I've pushed my app on an iPhone 3G up to 70 MB before, it just isn't likely to work for most, nor for long.
Requesting on the iTunes page that users restart their devices can help, though there's no guarantees it'll be effective.
Also, this is all assuming devices prior to the 3GS / 3rd Gen iPod Touch. If the app merely runs on an older device, it should have no problem on the newer ones (which have twice as much ram, 256 MB).
I think available memory may depend on several factors such as device model, how long it has not been rebooted etc.
You should not rely on some fixed values but instead try to use as little memory as possible and implement -(void)applicationDidReceiveMemoryWarning:(UIApplication *)application in your application delegate and/or -didReceiveMemoryWarning in your view controllers to handle low memory warnings there and free unused memory.
Is Activity Monitor (a.k.a. Memory Monitor) the only tool in Xcode Instruments that can measure the total app RAM usage of an iPhone app running in Simulator? Just that line showing momentary wired RAM?
And how accurate is that versus iPhone hardware, especially given OSX paging i/o to VM?
I'm seeing 7-8MB wired RAM figures for just the default Xcode iPhone project templates (other than OpenGL) compiled and running. At the same time Object Allocations shows well under 1MB for all objects.
Nope, there's a much better way to do it.
Go to the Run menu and select Run with Performance Tool then Object Allocations.
This will start Instruments and will show RAM usage. It's also useful for detecting memory leaks if you choose Leaks instead of Object Allocations.
I would agree, since the Simulator is just an "API simulator", the behavior you see is going to be at least somewhat dependent how OS X manages memory. And the restrictions are obviously different, for example you can exceed 128 MB of ram, or even 256 MB, which obviously isn't possible on any current iPhone or iPod Touch (at least, as of this writing...).
I've still found it useful in OpenGL for making sure textures and other items are properly deallocated, but beyond that, it's just a rough guideline.
However, if you want to see memory usage on device, there's a simple enough solution. Just target Device in Xcode, and go to Run > Run with Performance Tool > Object Allocations, then the build will be sent to the device and the Object Allocations tool will pop up next to Xcode and show on device memory usage.