# runBlocking Builder

Paul Tomoiu

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Examples,

Kotlin,

Coroutine

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Published 2022-09-24

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

Info

runBlocking is considered a Coroutine Builder as it creates a coroutine.
This new created coroutine will stop the current thread for running all we have defined inside it. When the coroutine will complete, the main thread will continue normally. This coroutine behaviour is atypical for a coroutine which run in parallel with the thread.

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.delay
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking
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")

	runBlocking {
		println("START: runBlocking I")
		launch {
			delay(2000L)
			println(">>>>>>>>>>>> runBlocking I >> launch 1")
		}
		launch {
			delay(1000L)
			println(">>>>>>>>>>>> runBlocking I >> launch 2")
		}
		println("runBlocking I - end")
	}

	println("END")
}

When we run this code we receive the following output:

START
START: runBlocking I
runBlocking I - end
>>>>>>>>>>>> runBlocking I >> launch 2
>>>>>>>>>>>> runBlocking I >> launch 1
END

Info

If instead launch method we will use GlobalScope.launch the execution behaviour will change as the new coroutine will have another scope.