# async Builder

Paul Tomoiu

●

Examples,

Kotlin,

Coroutine

●

Published 2022-09-24

This tutorial explains how we can use async in order to start a coroutine in Kotlin.

Info

async is considered a Coroutine Builder as it creates a coroutine.
async builder is similar to launch, but async will return also a value. This value is returned by a lambda expression.

Take a look at the following example created with Spring Boot 3.0, maven in Kotlin:

Demo1Application.java
package com.example.demo1

import kotlinx.coroutines.*
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class Demo1Application

suspend fun main(args: Array<String>) {
	runApplication<Demo1Application>(*args)

	println("START")

	val valueReturned1 = GlobalScope.async {
		println("START:   valueReturned1")
		delay(3000L)
		"My value returned 1"
	}
	val valueReturned2 = GlobalScope.async {
		println("START:   valueReturned2")
		delay(2000L)
		"My value returned 2"
	}
	val valueReturned3 = GlobalScope.async {
		println("START:   valueReturned3")
		delay(1000L)
		"My value returned 3"
	}
	println(valueReturned1.await())
	println(valueReturned2.await())
	println(valueReturned3.await())

	println("END")
}

When we run this code we receive the following output:

START
START:   valueReturned1
START:   valueReturned3
START:   valueReturned2
My value returned 1
My value returned 2
My value returned 3
END

Info

The "async" coroutines are started in a random manner (but almost in the same time).
await() method is waiting for the value to be returned.
println(valueReturned1.await()), println(valueReturned2.await()), println(valueReturned3.await()) run sequentially.