ThreadPoolDemo.kt

import java.util.concurrent.LinkedBlockingQueue
import java.util.concurrent.ThreadPoolExecutor
import java.util.concurrent.TimeUnit
import kotlin.random.Random.Default.nextInt


/*
* Here queue size is defined 3
* so that means if the tasks in the queue exceeds 3 then the pool will create
* a new thread for the task execution. The pool can created maximum 5 threads in this case.
* If Queue size is less than or equal 3 then ThreadPool will use minimum number of threads
*/
val pool = ThreadPoolExecutor(
    /* corePoolSize = */ 1,
    /* maximumPoolSize = */ 5,
    /* keepAliveTime = */ 0,
    /* unit = */ TimeUnit.MILLISECONDS,
    /* workQueue = */ LinkedBlockingQueue<Runnable>(3)
)

fun main() {
    printString()
}

fun printString() {
    for (i in 1..8) {
        pool.execute(getRunnable(i))
        if (i == 8) println("Called 8 Times")
    }
}

private fun getRunnable(taskNo: Int): Runnable {
    return Runnable {
        val delay = nextInt(3,12).toLong()
        println("Delaying $delay seconds for task no $taskNo")
        TimeUnit.SECONDS.sleep(delay)
        println("${Thread.currentThread().name} ------ Finished Task no: $taskNo")
    }
}