CoroutineScope

Learn structured concurrency with CoroutineScope.

What is CoroutineScope?

A CoroutineScope is the scope in which coroutines live. Every coroutine belongs to a scope; cancelling the scope cancels all child coroutines.

In Kotlin runBlocking creates a scope and blocks the thread until the block completes. You start a new coroutine inside it with launch, which returns a Job. In this lesson you will write your first coroutine with runBlocking and launch.

Scope with runBlocking

runBlocking creates a new CoroutineScope and waits until the block completes. Inside it you start new coroutines with launch.

Example: runBlocking { launch { println("Running") } }. Here runBlocking is the outer frame and launch is one coroutine. The message inside println is printed; the program ends when runBlocking returns.

Exercise Write your first coroutine

Open a scope with runBlocking. Start a coroutine with launch inside it that prints println("Hello coroutine"). The program ends when runBlocking finishes.

Show example solution

fun main() = runBlocking {
    launch {
        println("Hello coroutine")
    }
}

Test yourself

Which one starts a coroutine?
- launch
- println
- main
- val
Show answer

launch — launch starts a new coroutine.

Complete the CoroutineScope definition

val scope = CoroutineScope(____)

Show answer

val scope = CoroutineScope(Dispatchers.Default)

Match the coroutine parts

CoroutineScope

Scope
launch

Starts
Job

Return type
runBlocking

Waits

Next lesson: Dispatchers

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