kotlin_fundamentals_8.kt

fun taskT(): Job {
    return GlobalScope.launch(Dispatchers.IO) {
        println("Starting C on ${Thread.currentThread().name}\n")
        val resultT1 = t1()
        println("Starting task T2,T3 on ${Thread.currentThread().name}")
        val jobT2T3 = async {
            val resultT2 = t2(resultT1)
            val resultT3 = t3(resultT2)
            return@async resultT3
        }
        /*
        * Since task T4, T5 aren't dependant on task T2 or T3 using async 
        * for T2,T3 is a win for us since we can continue our execution.
        * Task 'T4' output is input to task 'T5'.
        *
        * Builder explanation: async is used as we need result from these 
        *      two tasks for our final result
        * Task name: T4, T5
        * Coroutine name: C4, C5 respectively
        * Thread pool: Since T4 is a file read and T5 we database write operation, 
        *      we use default thread pool for our combined coroutine
        * suspension: It won't suspend the calling function.
        * start context item : To demonstrate start keyword, we pass it as lazy 
        *      - meaning only start this async coroutine when await() is called.
        *
        * */
        println("Starting task T4,T5 on ${Thread.currentThread().name}\n")
        val jobT4T5 = async(Dispatchers.Default, start = CoroutineStart.LAZY) {
            println("Inside Task T4,T5 on ${Thread.currentThread().name}")
            val resultT4 = t4()
            val resultT5 = t5(scope = this, param4 = resultT4)
            return@async resultT5
        }
        // omitted code here
    }
}