AsyncSample.kt

import kotlinx.coroutines.experimental.*
import java.math.BigInteger
import java.util.concurrent.atomic.AtomicBoolean
import java.util.concurrent.atomic.AtomicLong
import kotlin.system.measureTimeMillis

fun main(args: Array<String>) = runBlocking<Unit> {
    var currN = AtomicLong(1);
    var isInterrupted = AtomicBoolean(false);
    var time = 0L;

    var currVal = BigInteger.valueOf(1);

    val fullTime = measureTimeMillis {
        val coroutine = launch {

            async {
                val c = System.`in`.read().toChar()
                when (c) {
                    's' -> {
                        println("currN=${currN.get()}")
                    }
                    'e' -> {
                        println("Interrupting...")
                        isInterrupted.set(true)
                    }
                }
            }

            while (!isInterrupted.get()) {

                time += measureTimeMillis {
                    currN.incrementAndGet()
                    currVal = currVal.multiply(BigInteger.valueOf(currN.get()))
                }

                if (currN.get() == 200_000L) {
                    println("currN=${currN} (currN=MAX_VALUE)")
                    isInterrupted.set(true)
                }
            }

        }
        coroutine.join()
    }

    print("Calculated factorial ${currN.get()}! with ${currVal.toString().length} digits; ")
    println("mesureTime=${time}ms fullTime=${fullTime}ms")
}

JuctAlgorithmSample.kt

import java.math.BigInteger
import kotlin.system.measureTimeMillis

fun main(args: Array<String>) {
    var currN = 1L;
    var currVal = BigInteger.valueOf(1);

    var time = measureTimeMillis {
        do {
            currN++;
            currVal = currVal.multiply(BigInteger.valueOf(currN))
        } while (currN < 200_000L)
    }

    print("Calculated factorial ${currN}! with ${currVal.toString().length} digits; time=${time}ms")
}

out

AsyncSample:
currN=200000 (currN=MAX_VALUE)
Calculated factorial 200000! with 973351 digits; mesureTime=17782ms fullTime=17835ms

JuctAlgorithmSample:
Calculated factorial 200000! with 973351 digits; time=17495ms