iOS Memory Deep Dive

WWDC 2018

didReceiveMemoryWarning( )

• Don’t necessarily assume that a memory warning is your cause.
  The warning will occur when user gets a call, message, etc.

Be careful when you delete a cache in the didReceiveMemoryWarning( )

Access the compressed dictionary → Decompress the dictionary (Memory Increased) → Delete the data

Result: Same allocations (Compressed Dictionary = Updated Dictionary)

Tools for Profiling Footprint

Memory resource exception

vmmap

• Virtual memory regions allocated in a process

vmmap + AWK

leaks

• Objects that are allocated, but no longer referenced

heap

• Objects allocated on the heap
• Useful for identifying large object in memory and what allocated it

Enabling malloc stack logging

malloc_history

• Backtraces for malloc and anonymous VM region allocations

Which tool to pick?

Images

• Stop using UIGraphicsBeginImageContextWithOptions
• Using UIGraphicsImageRenderer (iOS 10)
  Automatically picks best graphics format !

Downsampling

• ImageIO can read image sizes and metadata information without dirtying memory
• ImageIO can read resize images at cost of resized image only