Memory leaks using the Xcode memory graph debugger

Memory leaks can be thought of as memory that is allocated, but never released (and then no longer used by the App). When there are no references to a block or section of memory, there is no way to release it an it can’t be used again.

Prerequisites:

• Reference and value types
• MVVM architecture

Terminology

Instruments: Instruments are a set of application performance analyzes and visualizers integrated into Xcode.

Memory leak: A memory leak is a portion of memory that will never be used, yet is held onto forever. It is both a waste of space and can cause problems.

Memory footprint: the amount of memory that a program uses or references. The more resources that are used, the larger the footprint. If objects are not released the occupied memory will grow, leading to memory warning and crashes.

Automatic Reference Counting (ARC): ARC is a memory management feature (of the Clang compiler) that provides the reference counting for both Objective-C and Swift. The references may be weak or strong, and when a strong reference is declared the counter increases by one. Upon release, the counter decreases by 1 and when the reference count is 0 ARC can deallocate it from the memory heap (as it will be satisfied that the object is not in use). Since weak references do not increase the reference counter objects that are only held with a weak reference(s) are automatically released since the counter will be set to 0.

Retain cycles: This is the state when two objects hold strong references to one another. Since the first object’s reference count cannot be 0 until the second object is released, and the second object’s reference count cannot be 0 until the first objet is released neither object can be released! It is self-evident that it is not possible to create retain cycles with value types, as they are passed by value.

malloc: allocates a memory block of a given size and returns a pointer to the beginning of the block.

Malloc Stack: Gives the stack trace for memory leaks

Malloc Scribble: Gives Xcode more accurate results for memory leaks, by filling freed memory with a…