Memory leaks caused due to CoreFoundation Framework

I am developing an iPhone application which mainly makes use of the Address Book and database. After fetching about 3000 contacts from the address book, I am attaching string tags to the contacts (5 for each). I am saving my tags in the database.

For Load testing purpose i have added 10,000 tags to the App. But during the load testing of my application, I observed some memory leaks which were not related to the Application code but represents a set of Instruction sets. Also Instruments showed Foundation as the responsible library for the Leak (Extensive use of NSString,NSDictionary,NSArray which belongs to the Foundation framework). My application crashes after 10 - 15 mins of usage.The Crash report mentions, application c开发者_StackOverflow社区rashed due to low memory.

Memory profiling using CLANG shows zero leaks. How do i solve these memory leaks? Are these leaks the real culprit behind the crash? Are there any other tools available to check memory leaks?

I often find my leaks say they're caused by Core Foundation (or any other framework for that matter) but are really my own. With the exception of the Simulator, rarely will you find excessive leaking in the frameworks.

If you open up the detail panel to the right in Instruments you may find listed your App's methods in there. That will give you indication of where it could be coming from in your code. One leak can spring many other leaks, and you may have to find the top level culprit to get rid of the lower level ones.

You should not expect Clang to do anything but find the most obvious leaks. It's very handy, but that's it, just a helpful addition to compiling.

clang is not a leak checker. It only detects a small subset of issues.

For memory leak debugging you should focus on Instruments, specifically the Object Allocation and Leaks instruments. Be sure to understand the difference between leaks and other source of high memory usage though.

Once you've determined that objects are leaking, use Instruments to examine their allocation stack trace (so you can tell what object it is), and their retain/release history.

If it's not a leak, then I suggest investigating the instructions here:http://www.friday.com/bbum/2010/10/17/when-is-a-leak-not-a-leak-using-heapshot-analysis-to-find-undesirable-memory-growth/

Most likely you have code that is creating the foundation objects. Leaks shows you the place of allocation but that is generally due to a call your code made to create the object. You can look at the call chain in Instruments and go back along the call chain until you get to your code - that is the place where you are causing the allocation. Now, for that allocation, look at your memory handling for that object: Do you release it some time later?

There are lots of ways you can fail to release memory property so it would be hard to guess which one you might be hitting. Ones I see when helping people include allocating an object and assigning it to an instance variable via a property with the retain attribute, something like this:

@property (retain) NSString* myString;

...

self.myString = [[NSString alloc] initWithString: @"foo"];

the alloc+init creates a retained object, the self.myString = increments the retain count again. If coded correctly, the dealloc method releases the property via one of:

[myString release]; or self.myString = nil;

And that takes care of the retain added with the self.myString = but does NOT take care of the retain from creation. Solutions, ONE of the following:

myString = [[NSString alloc] initWithString: @"foo"]; // doesn't call the setter method so no assignment retain - but doesn't call the setter which might be bad if non-trivial setter.

self.myString = [[[NSString alloc] initWithString: @"foo"] autorelease];

autorelease releases the alloc+init retain.

Now of course this is a contrived example because you'd probably really use:

self.myString = [NSString stringWithString: @"foo"];

which is a class method returning an autoreleased string and avoids the problem. But the idea is to show a simple example to explain this type of issue.

There are many other ways to not release memory properly, but the advice to work your way back up the call-chain until you get to your code is the way to go look at where you are triggering the allocation of the memory and then you can figure out why you aren't releasing that properly.

Try to do some issues in u code: 1. Please avoid hide declaration like

NSString *string = [dictionary valueForKey:[dictionary2 valueForKey:@"something"]]

Correct code is:

NSString *key = [dictionary2 valueForKey:@"something"];  
NSString *string = [dictionary valueForKey:key];
key = nil;

1. Try to avoid declaration with autorelease and local declaration like:

   NSArray *array = [NSArray array];

If u do this, make sure that u have:

NSArray *array = [NSArray array];
.... some code where array is using;
array = nil;

Better idea is alloc and release immediately when u don't need object and put it to nil. 3. Check if u using correct setters. Probably better idea is avoid to using it, at my experience, deallocate class start leaks for getters and setters, which was using before.

If u post some part of u code, where u seen most leaks (instruments give u possibility to click on leaked objects and see volume of leaks in programming code) community can suggest more.