A handle to a coroutine you can cancel or wait on with join(). launch returns a Job; async returns Deferred which extends Job.

Does async always run in parallel?

async starts concurrent work within the same scope, but parallelism depends on dispatchers and available threads.

Intermediate 9 min readKotlin 2.0

Kotlin launch vs async — Jobs and Deferred Results

launch and async both start coroutines, but they serve different purposes. Pick launch when you do not need a return value; use async when you do.

What You Will Learn

Start work with launch (returns Job)
Compute results with async (returns Deferred)
Retrieve results using await()
Run multiple async tasks concurrently
Cancel work via Job

launch — Fire and Forget

launch starts a coroutine and returns a Job. Use it for side effects like logging, UI updates, or background sync when you do not need the result in the caller.

launch Example

kotlin
import kotlinx.coroutines.*

fun main() = runBlocking {
    val job = launch {
        delay(200)
        println("Work finished")
    }
    println("Started job: ${job.isActive}")
    job.join()
}

Output

Started job: true Work finished

job.join() waits for the launched coroutine to complete. isActive is true while it runs.

Dependency required: implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.9.0")

async and await — Get a Result

async returns Deferred<T>. Call await() to suspend until the result is ready. Multiple async blocks can run in parallel.

Parallel async

kotlin
import kotlinx.coroutines.*

suspend fun fetch(id: Int): Int {
    delay(100)
    return id * 10
}

fun main() = runBlocking {
    val a = async { fetch(1) }
    val b = async { fetch(2) }
    println(a.await() + b.await())
}

Output

Both fetch calls run concurrently. await() retrieves 10 and 20, then they are summed.

Practice Exercise

Exercisepredict output

What does this print? import kotlinx.coroutines.* fun main() = runBlocking { val d = async { 5 + 5 } println(d.await()) }

Quick Quiz

When should you prefer async over launch?

Kotlin launch vs async — Jobs and Deferred Results

What You Will Learn

launch — Fire and Forget

launch Example

async and await — Get a Result

Parallel async

Practice Exercise

Quick Quiz

Frequently Asked Questions

Related Tutorials