I've been building a browser feature for an app which obviously works with UIWebView. I've been seeing memory jump up when the browser opens which makes sense, however i'm seeing some troubling results during a leaks profile:
The VM: JS garbage collector and VM: WebCore purgeable data just keep climbing the more I browse. Whats even worse is that when the browser is deallocated and it's web view released, these objects are still there, taking up upwards of 6 MB of memory.
I'm not sure what if i'm not handling UIWebView correctly but there seems to be an issue with this memory being held on to after the UIWebView is deallocated.
I perform some cleanup prior to the browser being deallocated as detalled in this post http://www.codercowboy.com/code-uiwebview-memory-leak-prevention/ but this doesnt seem to be making any difference.
Has anyone had this issue? Any insight would be awesome. I've seen a few questions already related to UIWebView memory issues however they don't specifically detail the results of a profile.
I'm unsure if I would immediately consider this a problem. Those VMs only start when you add a web view to your view hierarchy and load a request with it.
It may just be the OS that keeps those resources alive in case they will be used again.
I tried to replicate your code that cleans up the data and had drops of 50%.
The JS Garbage collector was always at around 3MB minimum, but had maximums of 8MB
The WebCore purgeable data was always at around 700KB
You may also consider that this may be related to bad JavaScript that continues to live because of leaks in the JavaScript code.
Related
I have done my best to make sure that views are released when they are no longer needed and when pushing the app and then looking at the Debug Memory Graph I see that no objects are present that shouldn't be there. However when I look at the memory graph I can see that although the graph does sometimes bump back down, it still slowly trends upwards. An example is attached.
I am new to building large projects in iOS and am mostly asking is this normal? Is it simply impossible to free all used memory with ARC? Or is there still more debugging to be done here?
(app starts at ~15MB, ends up at 20.1MB)
Starting at 15 megabytes and levelling off at 20 megabytes is great. This app is tiny, and its memory usage levels off quickly. Problems arise when memory usage keeps rising forever, typically on the level of giga bytes, i.e. many orders of magnitude bigger! So, don't worry, be happy.
I’m currently working on a tvOS app. This is my first native (Swift) app. The app will be a digital signage app, used during events or in offices of companies.
One big difference compared to a typical app on iOS/tvOS is that it needs to run pretty much 24/7, so memory is a big topic for this app. The smallest leak will eventually cause the app to crash.
The app is constantly looping through a set of fullscreen slides. At the bottom of the screen there is a ticker with 10 articles (refreshed every 10 seconds - now during development). Below is a screenshot of the weather slide, to get an idea.

Currently the app is crashing after a period of time and I’m pretty sure I’ve narrowed it down to the ticker component (when disabling it, the app lives for days). If I use the ‘Leaks’ preset in Instruments I get the following result:

It looks like it’s leaking Article instances. I’m recreating Article instances every 10 seconds and providing them to the ticker component. I think that is why new instances leak every ~10 seconds.
Before I started using the ‘Leaks’ preset in Instruments, I used the ‘Allocations’ preset, while using this all seemed fine to me. But I’m probably misreading the results…
Using allocations:

The way I read this is that currently 10 Article instances exist in memory, and 31 have existed but are cleaned up now - so I’m safe.
But the app still crashes.
I’ve read a lot on retain cycles, implemented weak/unowned where I believe I should.
So my question is not so much about code, but more about how to read this data, what does a Leak mean in this context, and why do I see these ‘leaks’ not as persistent objects in the Allocations window?
(tests are done on multiple devices + simulator)
If you see a steady (i.e., approximately n GB / minute or hour) increase in memory usage in Instruments, that is a good sign that objects are being created, but not dealloced. Your allusion to weak and unowned vars makes me think that you know this, but you may not have found all sources of your leak. I would suggest taking a few generation summaries in Instruments, and looking at specific classes/objects in Heap allocations. Your problem classes will steadily increase in number, and likely never decrease. Try to debug the problem from there.
As for what 'leak' means in this context, it's what it always means: Your computer is not releasing memory resources. It may seem different, because we are used to thinking of a leak as something that eats through memory at a much faster rate (like an infinite loop running on four cores, or something), but that kind of leak and this are actually the same thing; yours is just slower.
I’m back after weeks trying to figure out what was wrong. The good news, I found my leak, and solved it!
The issue was solved by removing a closure inside another closure keeping a reference to a variable in the first closure. This caused a retain cycle.
I really don’t understand why I didn’t find it earlier, I asked a new question for this here: getting-different-data-in-instruments-based-on-method-of-profiling.
I am trying to work through some low memory conditions using instruments. I can watch memory consumption in the Physical Memory Free monitor drop down to a couple of MB, even though Allocations shows that All Allocations is about 3 MB and Overall Bytes is 34 MB.
I have started to experience crashing since I moved some operations to a separate thread with an NSOperationQueue. But I wasn't using instruments before the change. Nevertheless, I'm betting I did something that I can undo to stop the crashes.
By the way, it is much more stable without instruments or the debugger connected.
I have the leaks down to almost none (maybe a hundred bytes max before a crash).
When I look at Allocations, I only see very primitive objects. And the total memory reported by it is also very low. So I cant see how my app is causing these low memory warnings.
When I look at Heap Shots from the start up, I don't see more than about 3 MB there, between the baseline and the sum of all the heap growth values.
What should I be looking at to find where the problem is? Can I isolate it to one of my view controller instances, for example? Or to one of my other instances?
What I have done:
I powered the device off and back on, and this made a significant improvement. Instruments is not reporting a low memory warning. Also, I noticed that Physical Free Memory at start up was only about 7 MB before restarting, and its about 60 MB after restarting.
However, I am seeing a very regular (periodic) drop in Physical Free Memory, dropping from 43 MB to 6 MB (an then back up to 43 MB). I would like to knwo what it causing that. I don't have any timers running in this app. (I do have some performSelector:afterDelay:, but those aren't active during these tests.)
I am not using ARC.
The allocations and the leaks instruments only show what the objects actually take, but not what their underlaying non-object structures (the backing stores) are taking. For example, for UIImages it will show you have a few allocated bytes. This is because a UIImage object only takes those bytes, but the CGImageRef that actually contains the image data is not an object, and it is not taken into account in these instruments.
If you are not doing it already, try running the VM Tracker at the same time you run the allocations instrument. It will give you an idea of the type memory that is being allocated. For iOS the "Dirty Memory", shown by this instrument, is what normally triggers the memory warnings. Dirty memory is memory that cannot be automatically discarded by the VM system. If you see lots of CGImages, images might be your problem.
Another important concept is abandoned memory. This is memory that was allocated, it is still referenced somewhere (and as such not a leak), but not used. An example of this type of memory is a cache of some sort, which is not freeing up upon memory warning. A way to find this out is to use the heap shot analysis. Press the "Mark Heap" button of the allocations instrument, do some operation, return to the previous point in the app and press "Mark Heap" again. The second heap shot should show you what new objects have been allocated between those two moments, and might shed some light on the mystery. You could also repeat the operation simulating a memory warning to see if that behaviour changes.
Finally, I recommend you to read this article, which explains how all this works: http://liam.flookes.com/wp/2012/05/03/finding-ios-memory/.
The difference between physical memory from VM Tracker and allocated memory from "Allocations" is due to the major differences of how these instruments work:
Allocations traces what your app does by installing a tap in the functions that allocate memory (malloc, NSAllocateObject, ...). This method yields very precise information about each allocation, like position in code (stack), amount, time, type. The downside is that if you don't trace every function (like vm_allocate) that somehow allocates memory, you lose this information.
VM Tracker samples the state of the system's virtual memory in regular intervals. This is a much less precise method, as it just gives you an overall view of the current state. It operates at a low frequency (usually something like every three seconds) and you get no idea of how this state was reached.
A known culprit of invisible allocations is CoreGraphics: It uses a lot of memory when decompressing images, drawing bitmap contexts and the like. This memory is usually invisible in the Allocations instrument. So if your app handles a lot of images it is likely that you see a big difference between the amount of physical memory and the overall allocated size.
Spikes in physical memory might result from big images being decompressed, downsized and then only used in screen resolution in some view's or layer's contents. All this might happen automatically in UIKit without your code being involved.
I have the leaks down to almost none (maybe a hundred bytes max before a crash).
In my experience, also very small leaks are "dangerous" sign. In fact, I have never seen a leak larger than 4K, and leaks I usually see are a couple hundreds of bytes. Still, they usually "hide" behind themselves a much larger memory which is lost.
So, my first suggestion is: get rid of those leaks, even though they seem small and insignificant -- they are not.
I have started to experience crashing since I moved some operations to a separate thread with an NSOperationQueue.
Is there a chance that the operation you moved to the thread is the responsible for the pulsing peak? Could it be spawned more than once at a time?
As to the peaks, I see two ways you can go about them:
use the Time Profiler in Instruments and try to understand what code is executing while you see the peak rising;
selectively comment out portions of your code (I mean: entire parts of your app -- e.g., replace a "real" controller with a basic/empty UIViewController, etc) and see if you can identify the culprit this way.
I have never seen such a pulsating behaviour, so I assume it depends on your app or on your device. Have you tried with a different device? What happens in the simulator (do you see the peak)?
When I'm reading your text, I have the impression that you might have some hidden leaks. I could be wrong but, are you 100% sure that you have check all leaks?
I remember one particular project I was doing few month ago, I had the same kind of issue, and no leaks in Instruments. My memory kept growing up and I get memory warnings... I start to log on some important dealloc method. And I've seen that some objects, subviews (UIView) were "leaking". But they were not seen by Instruments because they were still attached to a main view.
Hope this was helpful.
In the Allocations Instrument make sure you have "Only Track Active Allocations" checked. See Image Below. I think this makes it easier to see what is actually happening.
Have you run Analyze on the project? If there's any analyze warnings, fix them first.
Are you using any CoreFoundation stuff? Some of the CF methods have ... strange ... interactions with the ObjC runtime and mem management (they shouldn't do, AFAICS, but I've seen some odd behaviour with the low-level image and AV manipulations where it seems like mem is being used outside the core app process - maybe the OS calls being used by Apple?)
... NB: there have also, in previous versions of iOS, been a few mem-leaks inside Apple's CF methods. IIRC the last of those was fixed in iOS 5.0.
(StackOVerflow's parser sucks: I typed "3" not "1") Are you doing something with a large number of / large-sized CALayer instances (or UIView's with CG* methods, e.g. a custom drawRect method in a UIView?)
... NB: I have seen the exact behaviour you describe caused by 2 and 3 above, either in the CF libraries, or in the Apple windowing system when it tries to work with image data that was originally generated inside CF libraries - or which found its way into CALayers.
It seems that Instruments DOES NOT CORRECTLY TRACK memory usage inside the CA / CG system; this area is a bit complex since Apple is shuffling back and forth between CPU and GPU ram, but it's disappointing that the mem usage seems to simply "disappear" when it clearly is still being used!
Final thought (4. -- but SO won't let me type that) - are you using the invisible RHS of Instruments?
Apple hardcoded Instruments to always disable itself everytime you run it (so you have to keep manually opening it). This is stupid, since some of the core information only exists in the RHS bar. But I've worked with several people who didn't even know it existed :)
I've kind of a weird issue with my iOS app.
after a while my app goes low in memory so memory warning, everything seems to be fine, but when I check the memory usage I noticed that all the calls to viewDidUnload didn't free up lot of memory, so after a few click in my app, it goes again in memory warning, everything seems to be fine again, but not a lot a memory have been released, so it goes again in memory warning faster, and then it crash (after the third memory warning most of the time). this crash is random : app freeze, app leaves, my debugger says app paused, but no bad access or sigbort, no zombies.
my guess is that memory warning can't free up enough memory has it should.
(I checked all my viewDidUnload and make nil every objects that are allocated in viewDidLoad)
Any help will be usefull !
thanks a lot.
So I managed to work with my issue.
I wrote "-(void) dealloc" methode in all my controllers and check if I enter in it as I should. (on pop controller, dissmiss etc..)
Every time it didn't, I do step by step in the controller to see what was retaining my controller from beeing dealloc.
most of the time it was some property that was not in "unsafe_unretained"
delegate that was in "ASSIGN" (and should not be in assign but in unsafe_unretained)
(heritage from non-ARC project...)
I also had some strange controller with XIB that was not deallocated even if empty.
I rebuild new one step by step with copy/paste and finaly with exactly the same code, the new controller was released, with no visible difference between then !!! gnneee
at least I know how to debug that kind issues now...
I don't think there's any way to give a specific answer without more data so the best I can do is suggest that you stop guessing what might be happening with your app and learn how to measure what is actually going on. Run your app under Instruments and you'll be able to check for leaks and also actually see what classes are responsible for the most of your application's memory footprint.
You should make sure you know how to use both the Leaks instrument to identify leaked object but also the Allocations instrument to identify orphaned (but not leaked) sets of objects which should have been released or just cases where your app is not responding to memory warnings as you expected.
https://developer.apple.com/library/ios/#documentation/developertools/conceptual/InstrumentsUserGuide/AboutTracing/AboutTracing.html might be a good place to start and there are a number of tutorials available as well; http://www.raywenderlich.com/2696/how-to-debug-memory-leaks-with-xcode-and-instruments-tutorial and http://www.friday.com/bbum/2010/10/17/when-is-a-leak-not-a-leak-using-heapshot-analysis-to-find-undesirable-memory-growth/ are among the first results I saw.
Vassily,
First, if you aren't yourself releasing extra memory, the the -didReceiveMemory warning does you no good and the OS will keep asking for memory until you are killed. This sounds like it is your problem.
Second, if that isn't the problem then you are probably getting terminated due to the size of your resident memory partitions. Make sure you look at your VM allocation in Instruments. I expect the MALLOC_TINY or MALLOC_SMALL both have greater than 5 MB resident and dirty footprints. Due to the nature of small allocations these VM regions will never shrink. The only option you really have is to not create a lot of small items in the first place. This is really only something you can address by changing you code's algorithms to use less memory.
Andrew
I have a strange memory issue I'm having problems resolving and would appreciate some advice as to where else to look.
The program I have (iPhone App) has a function whereby it basically downloads loads of files, processes those that are JSON, and stores the rest to disk. The JSON processing is CPU intensive and can take several seconds per file, so I have a NSOperationQueue with maxConcurrency limited to 1 that handles all the heavy lifting, and a queue that manages the multiple files to download.
Ever since iOS5 came out, the App has had problems completing the download sequence without crashing and so far what I have tried is;
1) Changed the performSelectorOnBackgroundThread JSON processing to use a single NSOperationQueue so as to limit the number of background threads working with large objects.
2) Added NSAutoReleasePools inside loops that create multiple, large, transient objects.
3) Flushed the sharedURLCache to ensure the files aren't hanging around in the system cache.
4) Stored the JSON objects to disk using NSKeyedArchiver and passed the filenames between threads rather than the actual objects, to again try to mitigate the number and size of retained objects currently in use.
All of these at first seemed to make a difference, and when I look at the memory allocations, I've now got the peak usage down from just over 20MB (hence no wonder it was crashing) to under 10MB, and yet the app is still crashing with low memory as before.
I'm trying to trace what is eating the memory causing the app to crash and on this occasion I'm having real problems persuading Instruments to tell me anything useful.
Here's a typical trace (on an iPhone 3GS running iOS 4.3.5)
You can see that the PEAK usage was a tad over 7MB and yet shortly after, you can see the 2 flags pertaining to low memory, and then low memory urgent, followed by the app terminating shortly thereafter.
If I use the memory monitor, the cause of the crash seems clear enough - physical memory is being exhausted - look at the light green trace below. The low memory warnings co-incide (not surprisingly) with the physical memory running out.
There are no leaks showing FWIW either (I've done that in other runs).
It's not image caches or NSURLConnection caches and the only thing I can think of is that perhaps there are some bad leaks that aren't being detected ... but I'm having issues identifying them because if I click into all allocations to see the objects that are live, and then do a command-A to select them all (in order to paste them into a spreadsheet to see where the memory seems to be), at the point I hit command-C to copy them, Instruments beachballs and never recovers.
I really cant figure out what's going on. Does anyone have some advice on how to persuade instruments to show me some more useful information about what is using this memory?
Sorry I can't post any meaningful code fragments ... hopefully the instruments screenshots at least give you an idea about where I'm coming from.
The Leaks instrument isn't terribly useful for figuring out anything but the obvious leaks in your app.
What you are describing is an ideal candidate for heapshot analysis.
tl;dr Heapshot analysis allows you to see exactly how the heap of your application grows between any two points of time (where you determine the points).