The use of a retain count has been around since the early day of iOS: The way this originally worked was that when you explicitly allocated an object it got a retain count of 1 and then when you called release or autorelease on that same object, its retain count was then decremented and the object was then collected. Therefore, to simplify, ARC keeps track of all the vars and lets that point to some class in the heap and tosses out classes form the heap when they are no longer referenced. This is done using two instance methods which all classes are expected to implement: retain increases the object’s reference count by 1, whereas conversely release decreases the object’s reference count by 1 and calls the instance method dealloc if the count reaches 0″. In the usual operation of the ARC system, “objects are allocated on the heap, and their lifetime is manually managed using a reference count.

There is a fair bit of overhead required in managing dynamically allocated memory, which is usually handled by the OS” (Ref#: S). The memory is typically allocated by the OS, with the application calling API functions to do this allocation. A program doesn’t really have runtime control over it it’s determined by the programming language, OS and even the system architecture” (Ref#S).Ĭontrastingly, “ the heap is a general term used for any memory that is allocated dynamically and randomly i.e. Because functions call other functions and then return, the stack grows and shrinks to hold information from the functions further down the call stack. The call stack “ stores information relevant to the current function such as a pointer to whichever function it was called from, and any local variables. Typically a call stack is composed of “ stack frames“ which are data structures that contain information about functions to call, these stack frames typically represent a function call and its argument data.

The terms “the stack” and “the heap” can have different meanings in different languages or programming environments, as they can be implemented in a variety of ways but there are usually similarities in how these data structures are utilized managing memory.īoth “the stack” and “the heap” are stored in RAM. It’s firstly important to know that value types (like structs) will be stored on “the stack”, whereas reference types (basically meaning classes) are dynamically managed on “the heap”. Let’s being with a quick refresher on how Swift and Objective-C work with memory management.

Xcode ios memory monitor