I am not sure what i am doing wrong here. Can anyb...

# coroutines

[Sachin Maharana]

I am not sure what i am doing wrong here. Can anybody point out the obvious. 😅

import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.launch
import kotlinx.coroutines.*
import kotlin.system.measureTimeMillis
import kotlinx.coroutines.delay

fun main() = runBlocking {
    println("${Thread.activeCount()} threads active at the start")
    val time = measureTimeMillis {
        createCoroutines(10_000)
    }
    println("${Thread.activeCount()} threads active at the end")
    println("Took $time ms")
}

suspend fun createCoroutines(amount: Int) {
    val jobs = ArrayList<Job>()
    for (i in 1..amount) {
        jobs += launch {
            delay(1000)
        }
    }
    jobs.forEach {
        it.join()
    }
}

[william]

what is your error / problem?

[bezrukov]

you're probably about unknown launch , right?
launch is a CoroutineScope's extension, so you need a scope to call it.

Here is an idiomatic way to write this:

fun main() = runBlocking {
    println("${Thread.activeCount()} threads active at the start")
    val time = measureTimeMillis {
        createCoroutines(10_000)
    }
    println("${Thread.activeCount()} threads active at the end")
    println("Took $time ms")
}

suspend fun createCoroutines(amount: Int) = coroutineScope {
    for (i in 1..amount) {
        launch {
            delay(1000)
        }
    }
}

[Sachin Maharana]

ahh..sorry i thought i made some stupid mistake. error is this.

e: /home/test/IdeaProjects/Coroutines/src/main/kotlin/main.kt: (29, 17): Unresolved reference: launch

[Sachin Maharana]

@bezrukov Yes. that works.Thanks. But i assumed, if i am using runBLocking in main , doesn't that gives scope to the createCoroutine function. and consequently launch could have been called without reference error?

[Sachin Maharana]

Also, is there a difference between runBlocking scope and coroutineScope?

[bezrukov]

But i assumed, if i am using runBLocking in main , doesn't that gives scope to the createCoroutine function.

No, to have a CoroutineScope as a receiver type for createCoroutines you need explicitly write it:
fun CoroutineScope.createCoroutines(amount....
but it is not recommended way.

Without it, where the compiler should take a scope, if you call this function from outside of runBlocking ?

Also, is there a difference between runBlocking scope and coroutineScope?

yes, runBlocking can be called from non-suspending fun, while coroutineScope can be only called from suspend fun.