Kotlin Coroutines with returning value

Question

I want to create a coroutine method which has returning value.

For example)

fun funA() = async(CommonPool) {
    return 1
}

fun funB() = async(Commo         


        

Answer 1

It may be late to answer this question but hopefully someone will find it useful. The code snippet below calculates sum of 3 values A + B + C. Each value is calculated independently in its own background thread in parallel and then all interim results consolidated into one final result and returned to the main thread to display it on a screen.

So it takes 5 seconds to calculate the final value (not 10 seconds = 2 + 3 + 5) and the result is 6 obviously and it's non-blocking, the main thread can handle other events while sum() execution is not complete.

suspend fun sum(scheduler: ThreadPoolExecutor): Int = coroutineScope {

    withContext(scheduler.asCoroutineDispatcher()) {
        val a = async { funA() }
        val b = async { funB() }
        val c = async { funC() }

        a.await() + b.await() + c.await()
    }
}

fun funA(): Int {
    Thread.sleep(2000L)
    return 1
}

fun funB(): Int {
    Thread.sleep(3000L)
    return 2
}

fun funC(): Int {
    Thread.sleep(5000L)
    return 3
}

class MainActivity : AppCompatActivity(), View.OnClickListener {
    private val tripletsPool = ThreadPoolExecutor(3, 3, 5L, TimeUnit.SECONDS, LinkedBlockingQueue())

   ...

    override fun onClick(view: View?) {
        if (view == null) {
            return
        }

        when (view.id) {
            R.id.calculate -> {
                GlobalScope.launch(Dispatchers.Main, CoroutineStart.DEFAULT) {
                    progressBar.visibility = View.VISIBLE
                    result.setText("${sum(tripletsPool)}")
                    progressBar.visibility = View.GONE
                }
            }
        }
    }
}