I use xcode 4.2 and this use ARC (Automatic Reference Counting).
This is not memory leak, because ARC send message of 'release':
NSNumber *xy = [[NSNumber alloc] init];
But it's possible to create memory leaks with this:
char *oldString = "Old String";
char newStrig = strdup(oldString);
I wanted to know that other types of memory leaks can be made?
(If is possible without using C or C++)
ARC only applies to Cocoa memory management. If you are casting between Cocoa and CoreFoundation for the toll-free bridge objects there are macros to transfer the memory-management.
You can leak memory in C, you can leak Core Foundation memory, and the static analyser helps with finding those.
ARC doesn't do away with memory management completely. It removes the need to manage memory for Cocoa objects and in some cases (because it can optimise away some retain release calls) is more efficient in managing memory, but you still need to understand memory management for Core Foundation objects, and for C memory.
You also need to understand Cocoa memory management to understand when to use strong, weak, or copy properties, and when to use Block_copy() and Block_release() on blocks, even though blocks are Cocoa objects and in most cases the correct memory management is handled for you with ARC.
Again; ARC doesn't do away with memory management. It simplifies it, and reduces the amount of code you have to write, but you still have to understand what is being done for you behind the scenes, and when you need to manage your own memory.
ARC can only work if you are using Objective-C memory allocations because its tied exclusively to that. In fact when you are using ARC the compiler does its best to match every alloc with an release (it cannot even guarantee that).
If you are using any other means than Objective-C allocations you are on your own again. ARC won't handle that.
Related
I'm studying Objective-C. I've found out about the ARC. I made a simple program with one class and one instance variable NSUInteger.
For educational purposes I'd like to examine the memory allocation/deallocation while the program is running.
Are there any console tools to see a program's memory? Or may be it is possible to do it in the Xcode itself? In other words I'd like to see the memory snapshot in different points in times when an object was allocated and then an object was deallocated.
Thank you.
First, NSUInteger variables are no objects in the meaning of Objective-C. They are handled with the C memory management. (Typically they are local vars on the stack, freed, when the local scope is left.)
So let's go to real instance objects of classes like NSNumber or NSString or – more important – MyCustomClass. You can see the whole processing of memory management, when you write a class and compile that with manual memory management. (This is possible via the compiler options. Select the project, go to build phases/compile sources and you will find an extra column compiler flags.)) Since ARC and MRC work together, ARC code will execute the MRC memory handling methods. Simply overwrite them in the MRC class and do some logging, set some breakpoints and so on.
But, this is very important, as long as you only deal with ARC code, you simply do not have to care about memory management. Maybe it is a good idea to learn that, but it is not something you have to do necessarily.
I fairly new to Obj-C and am just starting out making little useless programs to help further my knowledge. I wanted to make sure I wasn't making any memory leaks. Does anything in the '#autoreleasepool' automatically release it's memory when the program ends?
Also if there are any bad habits, please let me know!
int main(int argc, const char * argv[])
{
#autoreleasepool {
Fraction* fractionOne = [[Fraction alloc]init];
Fraction* fractionTwo = [[Fraction alloc]init];
Fraction* fractionThree = [[Fraction alloc]init];
[fractionOne setTo:1 over:2];
[fractionTwo setTo:1 over:4];
[fractionThree setTo:1 over:8];
[Fraction numberOfFractions];
return 0;
}
}
See Apple's discussion of Using Autorelease Pool Blocks in the Advanced Memory Management Programming Guide.
In short, no, it is not the case that "anything in the #autoreleasepool automatically release[s] its memory when the program ends" (or at least not as a function of the #autoreleasepool). The purpose in having an autorelease pool is to control when the memory is reclaimed from autorelease items, i.e. when will the pool be drained. But your code sample doesn't appear to employ any autoreleased items, so it is not really applicable here (unless the methods used autorelease objects internally).
The most common usage of autorelease pools is to reduce the memory high-water mark of your app. See Use Local Autorelease Pool Blocks to Reduce Peak Memory Footprint. It used to be used for thread programming, but now that we have operation and dispatch blocks, we don't have to write traditional threaded code anymore, so we don't have as many occasion to need separate autorelease pools in our multithreaded code.
With ARC turned on, code is added at compile time to explicitly release fractionOne, Two and Three, so they'll get released with ARC. Without ARC, the alloc is creating a retained instance of Fraction and your code hasn't either released explicitly (almost always better) or set these as autoreleased (almost always worse).
So without arc, you're leaking during the few milliseconds this program is running.
That's more or less what it does. But don't worry: just rely on ARC. It manages your memory for you!
Using ARC, the only place you'll really see #autoreleasepool is the main function. When you start making apps, you'll write your code elsewhere and will barely ever edit the "default" main function (given to you by the Xcode templates).
So don't worry about it! Your code is fine :)
The autorelease pool object is essentially a container during runtime that holds objects (so-called autoreleased objects) alive in memory until they are released, i.e. when the pool is drained. This will happen at the end of autorelease’s scope.
Autorelease Pool is part of the Manual Reference Counting (MRC) technique in Objective-C to manage an object’s lifecycle. MRC is one of the three memory management models, the other two being Automatic Garbage Collection and ARC (Automatic Reference Counting).
During runtime, we want to avoid having memory leaks. These are blocks of allocated memory (e.g. objects) that were once alive but are not referenced by any process anymore. If we have no way of accessing or releasing them by any other running code, they can create numerous issues, e.g. cluttering and reducing the amount of available memory. The concept of the Autorelease Pool helps to mitigate this risk.
References:
NSAutoreleasePool
Programming in Objective-C, Sixth Edition (2013) by Stephen G. Kochan
I'm using ARC, and my application compiles and works without crashing. However, when I run an Analyze build, I am seeing these warnings. I come from PHP and JavaScript so naturally I have no idea what to do to fix this stuff. Can anyone help me out?
ARC needs some help when dealing with Core Foundation. Try this:
NSArray *linkedPeople = (__bridge_transfer NSArray *)ABPersonCopyArrayOfAllLinkedPeople(person);
and
NSDictionary *personDictionary = (__bridge_transfer NSDictionary *)(ABMultiValueCopyValueAtIndex(addressFromPerson, 0));
__bridge_transfer tells ARC that a non-Objective-C (i.e., Core Foundation) pointer is being moved to an Objective-C pointer, and it allows ARC to take ownership of the object for memory management purposes. CF functions with the word "copy" in them produce an object reference with a +1 reference count. If you don't explicitly call CFRelease() on the object later, then it will leak. Using __bridge_transfer, however, lets ARC do this for you.
(Note: I didn't test this, but I believe those are the issues that the static analyzer is complaining about.)
Yes, you can use:
NSArray *linkedPeople = (__bridge_transfer NSArray *)ABPersonCopyArrayOfAllLinkedPeople(person);
But Apple now recommends using:
NSArray *linkedPeople = CFBridgingRelease(ABPersonCopyArrayOfAllLinkedPeople(person));
It does the same thing, but Apple recommends you use the latter.
See WWDC 2012 session 405, 37:33 into the presentation.
So! Even though you're using Automatic Reference Counting (ARC), it's still a good idea to read up on Objective-C Memory Management:
http://longweekendmobile.com/2011/09/07/objc-automatic-reference-counting-in-xcode-explained/
But, for your specific problem:
Generally, when you see a C method in the Apple frameworks that has the word Copy in it, you're taking ownership of that Core Foundation type and you need to release it. When you want to release that type, just use:
CFRelease(addressFromPerson)
That's the first issue. Your screenshot cuts off the second error so I'm only speculating, but I think you also need to release your NSDictionary *personDictionary. Similarly:
CFRelease(personDictionary)
Note that you also need to manage the memory for linkedPeople
Normally ARC will take care of memory management for you, but when working with Core Foundation types, you still need to clean up after yourself.
I would strongly recommend you check out these great resources on memory management with ARC, particularly when dealing with CF types and toll-free bridging:
http://www.joergjacobsen.com/blog/2011/10/05/managing-toll-free-bridging-in-an-arced-environment/
http://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html
I am getting a bit confused. I am creating an app with storyboard, and running it on iPad 1. the application uses a lot of memory, so reached the 120mb, crashes. accordingly to what I have understood to remove this problem you need to release, dealloc... the point is that with ARC this should be automatic. In fact if I add for e.g.: [label1 release]; it gives me an error. But this ARC automatic release and dealloc does not seem to work! Is this because there are different ways to release with ARC??
You don't need to manually retain/release/autorelease with ARC. However if you have active references to a lot of unused objects they will still remain in memory. Profile your app with Instruments and it will show you how many objects you're creating of each class and how much memory they're consuming.
With ARC you still need to think about memory usage you just don't need to worry as much about memory leaks.
NSObject *bigMemObj = [[BigMemClass alloc] init];
//This creates the object in memory. In both arc and manual counting the retain count is 1
//Do stuff
//Prior to ARC you would have had to call [bigMemObj release]; before setting the variable to nil
bigMemObj = nil
//With ARC you don't have to do anything. The compiler inserts the release at compile time
Also read the documentation on declaring iVars __strong vs __weak.
Without looking at your code it's hard to identify what is consuming all the memory but hopefully that should help you determine where to start looking.
You should implement #autoreleasePool{} inside each method. In essence, each method will look like the following:
-(void)methodName{
#autoreleasePool{
//do method stuff
}
}
This will ensure that, upon exiting the autoreleasePool, memory is properly released.
I can't vote this back up, otherwise I would. I think Alessandro is asking about ARC vs using release and dealloc, not about what he's loading!
So, Alessandro, your understanding is correct that with ARC you don't release or dealloc. Therefore, those won't work if you're using ARC. Also, there is no alternative to release/dealloc, since ARC doesn't use it.
My suggestion would be to look at what you're using in the app that is taking up all this memory. Do you have a large number of pictures, for example, that are very large? Keep any graphics as small as possible, matching the resolution of the iPad. Especially the iPad 1, which doesn't have the "retina display".
You can use Autorelease pools in ARC. Here is some documentation on when to use them:
NSAutoreleasePool Class Reference
Advanced Memory Management Programming Guide: About Memory Management
I'm thinking of writing an app for the iphone. But I'm confused in regards to the objective-c language. Am I correct in saying that I have to do my own memory management? Is Objective-C a managed language such as C# and/or Java?
Thank you!
"Managed" is a marketing term that has no technical meaning. Objective C for the iPhone is not garbage collected, but uses retain counting memory management. So in some sense, you have to do your own memory management, but it's limited to knowing the Cocoa retain counting methodology.
Edit: My comments on "managed" refer to a previous post version. The comment is left here because I'm tired of seeing the word.
There is no garbage collection feature. However, any object you copy, retain, alloc etc. has its retain count bumped up by one, and you are responsible for calling a releaseor an autorelease - you own an instance of that object. If you don't call [<YOUROBJECT> release]; or [<YOUROBJECT> autorelease];, the object remains in the iPhone's/iPod Touch's/iPad's memory, but the pointer no longer remains, and a memory leak occurs, as that bit of memory can no longer be accessed. Autoreleasing adds the object to the autorelease pool, and means that it will become released at some point in the future. Always use a standard release where possible, as autorelease means that it will still stay in the device's memory for a while, you can never be sure when it will be released, and it is a slightly more demanding method to call.
Never call dealloc on an object - releasing or autoreleasing is sufficient, and if required, the object will automatically be dealloced.
Make sure you never release objects you do not own, and if you do release objects, you release them after you no longer have any use of them - otherwise, you may try to access that object, and the device cannot find the object, and the situation results in your app crashing due to an EXEC_BAC_ACCESS error - to find out the root of the problem, open Instruments, add the Object Allocation instrument and enable NSZombie detection in its preferences (or add the Zombies instrument (only available in iPhone SDK 3.2+)). You can then view the entire history of the object which causes the problem, and jump to the exact line of code that caused the problem.
You can read more here.
Hope this helped
As others have pointed out Objective-C has no garbage collector on the iPhone, but it does have one for Mac OSX. Here is an article describing this in more detail: http://vasudevkamath.blogspot.com/2010/01/objective-c-my-opinions.html
You have to do your own memory management with Objective-C on the iPhone.
The answer isn't specific to Objective-C. If you're doing iPhone development, no...there is no garbage collector. If you're developing for Mac OSX, however, there is garbage collection.