Question

I’m performance tuning my iPhone/iPad app, it seems like not all the memory gets freed which should be. In instruments, after I simulate a memory warning in my simulator, there are lots of “Malloc” entries left; what’s about them? Can I get rid of them, what do they mean/what do they stand for?

Thanks a lot,

Stefan

Answer 1

At any time, your app will have a (huge) number of living objects, even after getting a memory warning (and the subsequent memory recovery by the operating system). So, it is pretty common that you will also see many of those mallocs you are seeing.

They are not in themselves a sign that something is wrong with memory allocation, but possibly only of the fact that your program is running.

Also have a look at this S.O. topic to learn more about the object allocation tool.

Furthermore, there are many advanced techniques you can use to detect memory allocation problems.
Here you can find a great tutorial that will allow you to go way beyond what the Leaks tool allows you to.

EDIT:

About the exact meaning of those mallocs, you have to think that you can allocate two broad classes of objects (to put it roughly): Objective-C objects that are created through the Obj-C runtime system, and “normal” C objects, that are allocated through malloc.

Many object of the second class are allocated (without you directly calling malloc) by system libraries and by the compiler C library (think about, e.g., sockets or file handles, whatever). Those (C) objects do not have type information associated to them, so Instruments simply shows you the size of the allocated memory block, without having more information available.

Many times malloc objects are created by higher-level classes, so that when you recover memory associated to their instances, also memory allocated through malloc is freed.

You should not worry specifically about them, unless you see that their overall size “grows indefinitely” along program execution. In such case you need first to investigate the way you alloc/release your higher level objects and understand where in your code things get stuck.