How can I make a coroutine print to another one? ...

# getting-started

[Ryan Zidago]

How can I make a coroutine print to another one?

If I do:

fun someFunction() = runBlocking {
  greet()
}

suspend fun greet() = coroutineScope {
  launch {
    delay(1_000)
    println("world!")
  }
  println("hello")
}

I will see both "hello" and "world!" printed, but the code is blocked until greet is done.

However if Iaunch greet inside a coroutine:

fun someFunction() = runBlocking {
  launch {
    greet()
  }
}

suspend fun greet() = coroutineScope {
  launch {
    delay(1_000)
    println("world!")
  }
  println("hello")
}

the code is non blocking anymore but I can't see any messages printed to the console 🤔

[Joffrey]

Which version of coroutines are you using? The standalone launch in your greet() function should not compile without coroutine scope 🤔

[Ryan Zidago]

My bad I forgot to add the coroutine scope.
I just edited my post.

[Joffrey]

That edited code works fine, and prints stuff. They are both equivalent because runBlocking waits for child coroutines to finish before returning. You can see it run here: https://pl.kotl.in/DHI3W7ifV

If you're not seeing this result, you should probably share the actual code you're using

[Ryan Zidago]

Here's what I have: https://play.kotlinlang.org/#eyJ2ZXJzaW9uIjoiMS42LjEwIiwiY29kZSI6InBhY2thZ2UgY29tLnJ5YW[…]hcIkhlbGxvXCIpXG59IiwicGxhdGZvcm0iOiJqYXZhIiwiYXJncyI6IiJ9

Sorry for the messy code; but I'm building a GraphQL server with Ktor and KgraphQL.

When a user creates a mutation, I want to have a coroutine print a message to the console after a certain time, let's say 1 minute, without blocking the execution of the code.

When I run the code above, I cannot see anything printed to the console.

[Ryan Zidago]

I've finally found the solution:

After having read this article, I've noticed that I needed to use the IO Dispatcher.

So the dummy code would look like this.