How do Image Loading Libraries like Coil or Glide do memory management?

Question

I am new to Android development. My app has use case where I want to download and display images from Internet. I am using Kotlin to build App and decided to use Coil library as Image loading library. While using my application, user's action my trigger download of multiple images. How do these image loading libraries make sure that memory/cache/disk space doesn't fill up? Do these libraries clear/delete images that were downloaded during last use?

Answer 1

The answer is going to depend on the particular library. But in general, they download the images to a file, to serve as a disk cache. That disk cache generally is kept to some limit in terms of size, with files being deleted on an LRU (least recently used) basis. They may then do the same with in memory representations, keeping the last N megabytes worth of images cached in a pool, ejecting on an LRU basis when needed. Ejecting them from the cache may or may not remove them from memory entirely- it depends on if any other reference to the object is maintained by client code. Some libraries allow configurable behavior on this, by either allowing client code to set size limits or provide entire cache implementations.

It's still possible for space to fill up. Especially memory- if you have too many bitmaps open and use up all available heap, then you're going OOM no matter what the loading library does. What the loading library will do is prevent multiple network requests for the same image, and prevent you from having to do all the cache management by hand.