Coroutines

Overview

• Provided by Kotlin to support and simplify the manage of asynchronous operation.

• Coroutines are asynchronous but not necessarily multi threaded.

Coroutines vs Threads

Coroutine	Threads
Lightweight threads	Expensive
Managed by user	Managed by OS
No context switching on processors	Threads are blocking

Threads

Coroutines

Coroutines Builder

• Coroutine have to be 'managed'. To manage a coroutine, it has to be launched inside a context which we called builder.

• The job of coroutine builder is launches a new coroutine concurrently with the rest of code.

launch

launch {
    delay(1000) 
    // delay is Kotlin suspending function to pause the coroutine without blocking the thread, 
    // so that thread can now be used for other coroutines while this coroutine is paused.
    println("Hello")
}

• launch simply returns a Job object

• Fire and forget type, can't return data

async

• async returns a Deferred object (like promise and future in other language)

• Perform task and return result

runBlocking

• runBlocking is a coroutine builder that runs a coroutine code, but blocks the main thread until the coroutine itself is finished.

• runBlocking can return a type

• Common place to use runBlocking is when you're writing test

Suspend Function

• A function with suspend modifier executes the code without blocking the thread where its running.

• Only allowed to be called from coroutine blocks or other suspend function.

Dispatcher

• Coroutine context / builder provide a Coroutine dispatcher.

• A Dispatcher determines which thread the coroutine is run on.