fromExecutor

fun Resource.Companion.fromExecutor(f: suspend () -> ExecutorService): Resource<CoroutineContext>

Creates a single threaded CoroutineContext as a Resource. Upon release an orderly shutdown of the ExecutorService takes place in which previously submitted tasks are executed, but no new tasks will be accepted.

import arrow.fx.coroutines.*
import java.util.concurrent.Executors
import java.util.concurrent.atomic.AtomicInteger
import kotlin.math.max

suspend fun main(): Unit {
val pool = Resource.fromExecutor {
val ctr = AtomicInteger(0)
val size = max(2, Runtime.getRuntime().availableProcessors())
Executors.newFixedThreadPool(size) { r ->
Thread(r, "computation-${ctr.getAndIncrement()}")
.apply { isDaemon = true }
}
}

pool.use { ctx ->
listOf(1, 2, 3, 4, 5).parTraverse(ctx) { i ->
println("#$i running on ${Thread.currentThread().name}")
}
}
}