Tomás Hanley

15th Oct 2018

Using Coroutines in your Android App

Why use Kotlin?

• Kotlin is a better language for the JVM than Java

  • Really easy to get up and running

  • Simpler language than Java

  • Much safer than Java

    • No more NullPointerExceptions!

    • Streamlines the handling of null values

  • More more clean & concise than Java

  • 100% Interoperable with Java

    • Kotlin & Java classes can live side by side

Androids Main Thread

• View Inflation

• Measure and Layout

• Draw

• Lots more

Mobile Refresh Rates

• 60Hz    -    16ms

• 90Hz    -    12ms

• 120Hz    -    8ms

We need async!

"Asynchronous or non-blocking programming is the new reality.

Whether we're creating server-side, desktop or mobile applications, it's important that we provide an experience that is not only fluid from the user's perspective, but scalable when needed."

How do we do async?

• AsyncTask

• Executors

• Loaders

• Future

• Libraries (like RxJava)

• Coroutines

Why Coroutines?

• Essentially, light weight threads

  • A new Thread uses 1MB
  • A new coroutine uses in the 10s of kilobytes
  • Suspended coroutine calls are removed from the stack

• A new way of managing background threads​

• Convert async callbacks for long-running tasks into sequential code

• Makes writing async code much easier

Coroutines vs RxJava

Coroutines can replace:

• Single / Maybe / Completable

• Not everything

• There are some Rx coroutine wrappers

Demo

Coroutine Scope

• For managing coroutine cancellation

• Parent-child relationship between coroutines

  • Ensures that cancelling a parent will cancel all its children

Demo

Dispatchers

• Controls where the coroutine is run

  • i.e. the threadpool

• Dispatchers.Default

  • Num CPU cores threads

• Dispatchers.IO

  • Min 64 threads

• Dispatchers.Main

Dispatchers

• withContext will run block in specified dispatcher

• When finished the coroutine will continue on the previous dispatcher

• Good way to switch threads briefly to handle expensive operations