No memory leaks, yet still running out of memory?

Question

In my cocos2d application I have run through it using instruments and removed all memory leaks. I have my game outputting how much memory is in use on the screen and it is constantly rising as the game progresses until I eventually run out of memory. The amount of objects on screen doesn't increase by very much each level. Its a fairly simple game so i should not be running out of memory so soon.

I am removing all objects from a level when it ends and reallocating new ones when a new level begins. Instruments tells me there are no memory leaks. When i run through instruments to show me where the allocations are the bulk of the problem doesn't seem to come from one place its all of my objects.

Any ideas what the issue might be?

Answer 1

Just because instruments doesn't show leaks, doesn't mean you're not still allocating memory you're not using. Pay attention to the ObjectAlloc graph and see if that is constantly rising without falling off.

Answer 2

If you allocate memory that you aren't using and can't clean up, that's just as bad as a leak, even though you haven't technically leaked anything because you've stashed some unused reference somewhere.

Look at how much memory you actually need to use or to keep for future use at any point in your app, then treat anything else previously allocated as a leak and fix it.

Answer 3

In Objective-C when using autorelease objects be wary of circular dependencies!

If you create object A and then an instance of object B and pass A to it, so that B retains A, and A also retains B (for example by adding it as child to A) you can easily setup a circular dependency and thus both objects won't be released.

Tip: add a -(void) dealloc method to all your scene classes, and set a breakpoint there. If you change a scene and its dealloc method isn't called after the scene transition has finished, you're leaking this scene (it's not released).

Try to find that leak by looking for a setup that's similar to the one I described above.

Answer 4

Be careful about autoreleased objects, since they are not released immediately. If you have sections with lots of allocations and autoreleasing, try using specific autorelease pools on them. It happened to me when creating huge decision trees (using NSArrays) for a game AI.

Answer 5

A great way to check for objects that are aggregating in memory is to use Instruments' new (in Xcode 3.2.3) Heap Shot functionality.

Use the normal Allocations instrument against your running application. Perform a series of repetitive events that should come back to some known state (for example, go one level down in a navigation controller and come back). Every time you do this, click on the Mark Heap button in the left sidebar for the Allocations instrument (under the section heading Heapshot Analysis).

What this will do is mark the heap at each of the starting points for this repetitive action and compare the objects that have been created by that point with the objects that had been created by the time you marked the heap last. Only objects that have been created between those two points and are still alive in memory will be listed.

If you are accumulating objects, but they are either not leaks or are being missed by the Leaks tool, they should show up here. I've found a number of subtle memory buildups this way, particularly when you pair this with the UI Automation instrument to automate the repetitive actions you're testing.

Answer 6

The bulk of the problem seem to be that Sprites don't get released in cocos2d unless all actions have been stopped on those sprites. This is done using stopAllActions. Cheers for all the suggestions.