Async won't compile because of multiple implementations in source

Question

I am trying to run the following code but it's not running because the compiler doesn't know which version of the async method to call. How do I tell it which one to call?

v

ar counter=0
val workerA=asyncIncrement(5000)
val workerB=asyncIncrement(100)
workerA.await()
workerB.await()

print("counter = $counter")

fun asyncIncrement(by:Int)=async{
    for(i in 1..by){
        counter++
    }
}

Just copy and paste the code into a scratch file or wherever and you should see the same compiler error

Answer 1

From Kotlin 1.3 you need to call async on a scope. In this example I have chosen the GlobalScope . But it doesn't matter which scope you choose, you always have to explicitly import the async extension function;

import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.async
import kotlinx.coroutines.runBlocking
import java.util.concurrent.atomic.AtomicInteger


fun main(args: Array<String>) {

    val counter=AtomicInteger(0)

    fun asyncIncrement(by:Int)= GlobalScope.async{
        for(i in 1..by){
            counter.incrementAndGet()
        }
    }

    val workerA=asyncIncrement(5000)
    val workerB=asyncIncrement(100)
    runBlocking {
        workerA.await()
        workerB.await()
    }

    print("counter = $counter")
}

BTW: I changed the variable counter from int to an AtomicInteger because the two async blocks may run in different threads. And I introduced runBlocking , because await has to run in a suspend function.