kotlin_fundamentals_9.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
        }
        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
        }
        // delay so that task T2,T3 starts and T4,T5 doesn't,
        // to demonstrate use of CoroutineStart.
        delay(100)
        println("Going to await result of task T2,T3 and T4,T5")

        // Now we await the result of task T2,T3 and T4,T5
        // and then combine their result.

        // await() is a suspend function which either
        // suspends the execution of calling function
        // if the deferred doesn't hold the value or
        // will return the result instantly.
        // Suspension: Will suspend the calling coroutine
        //
        // Note: Here it may so happen that jobT2T3 await
        // gives the result back and then we call await on
        // jopT4T5 and it'll return the result immediately
        // since it already computed it while t2 and t3 were executing.
        // This is an example where calling a suspend function doesn't
        // result in a suspension even though we were launching coroutines
        // inside it because the result was already calculated
        // by the time await was called.
        val combinedResult = jobT2T3.await() + "_" + jobT4T5.await()

        // After the await() calls for both tasks are done,
        // the jobs are now in the completed state.
        println("\nThe final result is $combinedResult")
    }
}