Hands-On Design Patterns with Kotlin

Coroutines under the hood

So, we've mentioned a couple of times the following facts:

• Coroutines are like light-weight threads. They need less resources that regular threads, so you can create more of them.
• Coroutines use thread pool behind the scenes.
• Instead of blocking an entire thread, coroutine suspends.

But how does that actually work?

Let's see an abstract example. How would we compose a user profile?

fun profile(id: String): Profile {    val bio = fetchBioOverHttp(id) // takes 1s    val picture = fetchPictureFromDB(id) // takes 100ms    val friends = fetchFriendsFromDB(id) // takes 500ms    return Profile(bio, picture)}

Summing up, our function now takes around 1.6 seconds to complete.

But we've learned about threads. Let's refactor this function ...