launch

Learn to start coroutines with GlobalScope.launch.

launch

launch starts a new coroutine inside a coroutine scope. It works fire-and-forget and returns no result. Example: runBlocking { launch { println("Ran") } }.

launch returns a Job; you can call join() to wait for it. Thanks to structured concurrency runBlocking does not return until all inner launch calls finish. This means coroutines complete even without an explicit join call.

launch and join

A launch block runs sequentially in its own coroutine. The println lines inside appear in the order written. Example: launch { println("First"); println("Second") } gives deterministic output.

Multiple launch calls can start at once; their order is nondeterministic. For deterministic output use sequential println inside a single launch. join() waits for a coroutine to finish; this helps when ordering matters. delay can also affect ordering.

Exercise Write two lines with launch

Add import kotlinx.coroutines.*. Write fun main() = runBlocking; inside call launch { println("First"); println("Second") }. A single launch with sequential writes gives deterministic output.

Show example solution

import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        println("First")
        println("Second")
    }
}

Test yourself

Complete the launch call

runBlocking {
    ____ { println("Started") }
}

Show answer

runBlocking {
    launch { println("Started") }
}

Match the launch concepts

launch

Start
Job

Return
join()

Wait
fire-and-forget

No result
What does launch return?
- A value
- Job
- Unit
- Deferred
Show answer

Job — launch returns a Job; you can wait with join().

Next lesson: suspend

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