Kotlin CoRoutines in NutShell!

API.kt

package com.example.croutinesdemo

import retrofit2.Call
import retrofit2.Response
import retrofit2.http.GET

//  api
interface API {
    @GET("/comments")
    fun getComments(): Call<List<Comment>>  //  apiCallWithRetrofitDemo1(), apiCallWithRetrofitDemo2()

//    @GET("/comments")
//    suspend fun getComments(): Response<List<Comment>>  //  apiCallWithRetrofitDemo1(), apiCallWithRetrofitDemo2()
}

MainActivity.kt

package com.example.croutinesdemo

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.lifecycle.lifecycleScope
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import retrofit2.Retrofit
import retrofit2.await
import retrofit2.awaitResponse
import retrofit2.converter.gson.GsonConverterFactory
import kotlin.system.measureTimeMillis

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        println("yup hello from ${Thread.currentThread().name}")
//        basicCoroutine1()
//        suspendFunc2()
//        contextSwitching3()
//        runBlockingDemo4()
//        jobJoinDemo5()
//        jobCancelDemo5()
//        jobCancel2Demo5()
//        jobCancel3Demo5()
//        jobCancel4Demo5()
//        asyncAwait1Demo6()
//        asyncAwait2Demo6()
//        asyncAwait3Demo6()
//        customScopes1Demo7()
//        customScopes2Demo7()
//        setUpRetroFit()
//        apiCallWithRetrofitDemo1()
//        apiCallWithRetrofitDemo2()
//        apiCallWithRetrofitDemo3()
    }

//    private fun apiCallWithRetrofitDemo3() {
//        GlobalScope.launch(Dispatchers.IO) {
//            val response = apiService.getComments()
//            if (response.isSuccessful) {
//                response.body()?.forEach {
//                    println("yup: it is comment: $it")
//                }
//            }
//        }
//    }

    private fun apiCallWithRetrofitDemo2() {
        GlobalScope.launch(Dispatchers.IO) {
            val response = apiService.getComments().awaitResponse()
            if (response.isSuccessful) {
                response.body()?.forEach {
                    println("yup: it is comment: $it")
                }
            }
        }
    }

    private val BASE_URL = "https://jsonplaceholder.typicode.com"
    private lateinit var apiService: API

    private fun setUpRetroFit() {
        apiService = Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build()
            .create(API::class.java)
    }

    private fun apiCallWithRetrofitDemo1() {
        GlobalScope.launch(Dispatchers.IO) {
            val comments = apiService.getComments().await()
            comments.forEach {
                println("yup: it is comment: $it")
            }
        }
    }

    private fun customScopes2Demo7() {
        //  this is best practice - similarly
        /*
                * 2020-09-16 00:47:01.567 14972-14972/com.example.croutinesdemo I/System.out: yup hello from main
        2020-09-16 00:47:04.703 14972-14972/com.example.croutinesdemo I/System.out: yup: still running!
        2020-09-16 00:47:05.706 14972-14972/com.example.croutinesdemo I/System.out: yup: still running!
        2020-09-16 00:47:06.708 14972-14972/com.example.croutinesdemo I/System.out: yup: still running!
        2020-09-16 00:47:07.712 14972-14972/com.example.croutinesdemo I/System.out: yup: still running!
        2020-09-16 00:47:08.726 14972-14972/com.example.croutinesdemo I/System.out: yup: still running!
        */
        tvDummy.setOnClickListener {
            //  bad practice
            lifecycleScope.launch {
                while (true) {
                    delay(1000L)
                    println("yup: still running!")
                }
            }
            //  launch another coroutine
            GlobalScope.launch {
                delay(5000L)
                startActivity(Intent(this@MainActivity, SecondActivity::class.java))
                finish()
            }
        }
    }

    private fun customScopes1Demo7() {
        //  it's bad practice - since we used global scope, instead of activity scope
        /*
                    * 2020-09-16 00:43:55.669 14849-14849/com.example.croutinesdemo I/System.out: yup hello from main
            2020-09-16 00:43:59.872 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:00.875 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:01.877 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:02.881 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:03.884 14849-14904/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:04.893 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:05.895 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:06.897 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:07.900 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:08.903 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:09.907 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:10.910 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:11.912 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:12.915 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:13.929 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:14.932 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:15.934 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:16.936 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:17.939 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:18.944 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
            2020-09-16 00:44:21.576 14849-14903/com.example.croutinesdemo I/System.out: yup: still running!
* */
        tvDummy.setOnClickListener {
            //  bad practice
            GlobalScope.launch {
                while (true) {
                    delay(1000L)
                    println("yup: still running!")
                }
            }
            //  launch another coroutine
            GlobalScope.launch {
                delay(5000L)
                startActivity(Intent(this@MainActivity, SecondActivity::class.java))
                finish()
            }
        }
    }

    private fun asyncAwait3Demo6() {
        //  this is BEST practice
        GlobalScope.launch(Dispatchers.IO) {
            val time = measureTimeMillis {
                val ans1: Deferred<String> = async { doNetworkCall1() }
                val ans2: Deferred<String> = async { doNetworkCall2() }
                println("yup: ans1: ${ans1.await()}")
                println("yup: ans2: ${ans2.await()}")
            }
            println("yup it took: $time ms!")   //  3 sec - which is desirable
        }
    }

    private fun asyncAwait2Demo6() {
        //  this is BAD practice
        GlobalScope.launch(Dispatchers.IO) {
            val time = measureTimeMillis {
                var ans1: String? = null
                var ans2: String? = null
                val job1 = launch { ans1 = doNetworkCall1() }
                val job2 = launch { ans2 = doNetworkCall2() }
                job1.join()
                job2.join()
                println("yup: ans1: $ans1")
                println("yup: ans2: $ans2")
            }
            println("yup it took: $time ms!")   //  3 secs - each request executes async but more boiler plate code
        }
    }

    private fun asyncAwait1Demo6() {
        //  this is BAD practice
        /*
      * 2020-09-16 00:18:18.177 14066-14066/com.example.croutinesdemo I/System.out: yup hello from main
        2020-09-16 00:18:24.566 14066-14117/com.example.croutinesdemo I/System.out: yup: resp1: this is resp1
        2020-09-16 00:18:24.567 14066-14117/com.example.croutinesdemo I/System.out: yup: resp2: this is resp2
        2020-09-16 00:18:24.567 14066-14117/com.example.croutinesdemo I/System.out: yup it took: 6082 ms!
        * */
        //  it'll take tot 6 secs to print result
        GlobalScope.launch(Dispatchers.IO) {
            val time = measureTimeMillis {
                val resp1 = doNetworkCall1()    //  3 sec
                val resp2 = doNetworkCall2()    //  3 sec
                println("yup: resp1: $resp1")
                println("yup: resp2: $resp2")
            }
            println("yup it took: $time ms!")   //  6 secs - which is undesirable
        }
    }

    private fun jobCancel4Demo5() {
        /*
        * with timeout
        *
        *
      * 2020-09-15 23:28:18.585 13481-13481/com.example.croutinesdemo I/System.out: yup hello from main
        2020-09-15 23:28:18.844 13481-13535/com.example.croutinesdemo I/System.out: yup: coroutine started!
        2020-09-15 23:28:20.721 13481-13535/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 30, res: 832040
        2020-09-15 23:28:20.755 13481-13535/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 31, res: 1346269
        2020-09-15 23:28:20.820 13481-13535/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 32, res: 2178309
        2020-09-15 23:28:20.889 13481-13535/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 33, res: 3524578
        2020-09-15 23:28:21.023 13481-13535/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 34, res: 5702887
        2020-09-15 23:28:21.298 13481-13535/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 35, res: 9227465
        2020-09-15 23:28:21.842 13481-13535/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 36, res: 14930352
        2020-09-15 23:28:21.842 13481-13535/com.example.croutinesdemo I/System.out: yup: coroutine ended!
        * */
        GlobalScope.launch(Dispatchers.Default) {
            println("yup: coroutine started!")
            withTimeout(1000L) {    //  cancels automatically after 1sec
                //  long running work
                for (i in 30..40) {
                    if (isActive)
                        println("yup: fib calculated, for i: $i, res: ${fib(i)}")
                }
            }
            println("yup: coroutine ended!")
        }
    }

    private fun jobCancel3Demo5() {
        /*
        *
        * it's cancelling properly
          * 2020-09-15 23:23:32.312 13222-13222/com.example.croutinesdemo I/System.out: yup hello from main
            2020-09-15 23:23:32.313 13222-13275/com.example.croutinesdemo I/System.out: yup: coroutine started!
            2020-09-15 23:23:32.338 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 30, res: 832040
            2020-09-15 23:23:32.365 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 31, res: 1346269
            2020-09-15 23:23:32.412 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 32, res: 2178309
            2020-09-15 23:23:32.467 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 33, res: 3524578
            2020-09-15 23:23:32.573 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 34, res: 5702887
            2020-09-15 23:23:32.774 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 35, res: 9227465
            2020-09-15 23:23:33.017 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 36, res: 14930352
            2020-09-15 23:23:33.314 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 37, res: 24157817
            2020-09-15 23:23:33.314 13222-13222/com.example.croutinesdemo I/System.out: yup: cancel called!
            2020-09-15 23:23:33.314 13222-13222/com.example.croutinesdemo I/System.out: yup: main thread continuing it's work!
            2020-09-15 23:23:33.958 13222-13275/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 38, res: 39088169
            2020-09-15 23:23:33.958 13222-13275/com.example.croutinesdemo I/System.out: yup: coroutine ended!
        * */
        val job = GlobalScope.launch(Dispatchers.Default) {
            println("yup: coroutine started!")
            //  long running work
            for (i in 30..40) {
                if (isActive)
                    println("yup: fib calculated, for i: $i, res: ${fib(i)}")
            }
            println("yup: coroutine ended!")
        }
        runBlocking {
            delay(1000L)
            job.cancel()
            println("yup: cancel called!")
            println("yup: main thread continuing it's work!")
        }
    }

    private fun jobCancel2Demo5() {
        /*

        it's not getting cancelled, because coroutine is busy doing the calculation within the loop
        *
          * 2020-09-15 23:20:42.064 13102-13102/com.example.croutinesdemo I/System.out: yup hello from main
            2020-09-15 23:20:42.162 13102-13161/com.example.croutinesdemo I/System.out: yup: coroutine started!
            2020-09-15 23:20:42.182 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 30, res: 832040
            2020-09-15 23:20:42.210 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 31, res: 1346269
            2020-09-15 23:20:42.242 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 32, res: 2178309
            2020-09-15 23:20:42.303 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 33, res: 3524578
            2020-09-15 23:20:42.370 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 34, res: 5702887
            2020-09-15 23:20:42.500 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 35, res: 9227465
            2020-09-15 23:20:42.699 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 36, res: 14930352
            2020-09-15 23:20:43.002 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 37, res: 24157817
            2020-09-15 23:20:43.181 13102-13102/com.example.croutinesdemo I/System.out: yup: cancel called!
            2020-09-15 23:20:43.181 13102-13102/com.example.croutinesdemo I/System.out: yup: main thread continuing it's work!
            2020-09-15 23:20:43.515 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 38, res: 39088169
            2020-09-15 23:20:44.304 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 39, res: 63245986
            2020-09-15 23:20:45.563 13102-13161/com.example.croutinesdemo I/System.out: yup: fib calculated, for i: 40, res: 102334155
            2020-09-15 23:20:45.563 13102-13161/com.example.croutinesdemo I/System.out: yup: coroutine ended!
        *
        * */
        val job = GlobalScope.launch(Dispatchers.Default) {
            println("yup: coroutine started!")
            //  long running work
            for (i in 30..40) {
                println("yup: fib calculated, for i: $i, res: ${fib(i)}")
            }
            println("yup: coroutine ended!")
        }
        runBlocking {
            delay(1000L)
            job.cancel()
            println("yup: cancel called!")
            println("yup: main thread continuing it's work!")
        }
    }

    private fun fib(n: Int): Int {
        return if (n == 0) 0
        else if (n == 1) 1
        else fib(n - 1) + fib(n - 2)
    }

    private fun jobCancelDemo5() {
        /*
        *   2020-09-15 23:14:21.792 12876-12876/com.example.croutinesdemo I/System.out: yup hello from main
            2020-09-15 23:14:21.888 12876-12911/com.example.croutinesdemo I/System.out: yup: this coroutine is running!
            2020-09-15 23:14:22.902 12876-12911/com.example.croutinesdemo I/System.out: yup: this coroutine is running!
            2020-09-15 23:14:23.905 12876-12876/com.example.croutinesdemo I/System.out: yup: job cancelled!
            2020-09-15 23:14:23.905 12876-12876/com.example.croutinesdemo I/System.out: yup: main thread is continuing!
        * */
        val job = GlobalScope.launch(Dispatchers.IO) {
            repeat(5) {
                println("yup: this coroutine is running!")
                delay(1000L)
            }
        }
        runBlocking {
            delay(2000L)
            job.cancel()
            println("yup: job cancelled!")
            println("yup: main thread is continuing!")
        }
    }

    private fun jobJoinDemo5() {
        /*
          * 2020-09-15 23:03:47.041 12085-12085/com.example.croutinesdemo I/System.out: yup hello from main
            2020-09-15 23:03:47.275 12085-12144/com.example.croutinesdemo I/System.out: yup: CoRoutine is running!
            2020-09-15 23:03:48.298 12085-12144/com.example.croutinesdemo I/System.out: yup: CoRoutine is running!
            2020-09-15 23:03:49.301 12085-12144/com.example.croutinesdemo I/System.out: yup: CoRoutine is running!
            2020-09-15 23:03:50.313 12085-12144/com.example.croutinesdemo I/System.out: yup: CoRoutine is running!
            2020-09-15 23:03:51.316 12085-12144/com.example.croutinesdemo I/System.out: yup: CoRoutine is running!
            2020-09-15 23:03:52.322 12085-12085/com.example.croutinesdemo I/System.out: yup: main thread continuing!
        * */
        val job = GlobalScope.launch(Dispatchers.Default) {
            repeat(5) {
                println("yup: CoRoutine is running!")
                delay(1000L)
            }
        }
        runBlocking {
            job.join()
            println("yup: main thread continuing!")
        }
    }

    private fun runBlockingDemo4() {
//         1
        //  create coroutine in main thread or whatever thread, and blocks the respective thread
//        println("yup before run blocking")
//        runBlocking {
//            println("yup inside run blocking, before delay")
//            delay(5000L)
//            println("yup inside run blocking, after delay")
//        }
//        println("yup after run blocking")

//        2
//        runBlocking {
//            /*
//            * o/p
//              * 2020-09-15 21:50:06.557 11180-11180/com.example.croutinesdemo I/System.out: yup hello from main
//                2020-09-15 21:50:06.558 11180-11180/com.example.croutinesdemo I/System.out: yup 2nd inside run blocking, before delay
//                2020-09-15 21:50:09.560 11180-11235/com.example.croutinesdemo I/System.out: yup finished IO co routine
//                2020-09-15 21:50:11.561 11180-11180/com.example.croutinesdemo I/System.out: yup 2nd inside run blocking, after delay
//            * */
//            launch(Dispatchers.IO) {
//                delay(3000L)
//                println("yup finished IO co routine")
//            }
//            println("yup 2nd inside run blocking, before delay")
//            delay(5000L)
//            println("yup 2nd inside run blocking, after delay")
//        }

        //  3
        runBlocking {
            /*
            * o/p

                    2020-09-15 21:51:52.771 11319-11319/com.example.croutinesdemo I/System.out: yup hello from main
                    2020-09-15 21:51:52.909 11319-11319/com.example.croutinesdemo I/System.out: yup 2nd inside run blocking, before delay
                    2020-09-15 21:51:57.978 11319-11319/com.example.croutinesdemo I/System.out: yup 2nd inside run blocking, after delay
                    2020-09-15 21:52:00.987 11319-11371/com.example.croutinesdemo I/System.out: yup finished IO co routine
            * */
            println("yup 2nd inside run blocking, before delay")
            delay(5000L)
            launch(Dispatchers.IO) {
                delay(3000L)
                println("yup finished IO co routine")
            }
            println("yup 2nd inside run blocking, after delay")
        }
    }

    private fun contextSwitching3() {
        GlobalScope.launch(Dispatchers.Main) {
            //  updating UI
            println("yup: I'm CoRoutine that runs in Main Thread:  ${Thread.currentThread().name}")
        }

        GlobalScope.launch(Dispatchers.IO) {
            //  api calls, db operation, file r/w etc
            println("yup: I'm CoRoutine that runs in worker Thread:  ${Thread.currentThread().name}")
        }

        GlobalScope.launch(Dispatchers.Default) {
            //  such as sorting 10,000 items in list
            println("yup: I'm CoRoutine that runs in worker Thread, suitable for long running process:  ${Thread.currentThread().name}")    //  let the thread name = `worker2`

            GlobalScope.launch(Dispatchers.Unconfined) {
                //  not confined to any thread, it'll run in the thread where this launch/suspend function is called
                println("yup: I'm CoRoutine that runs in UnConfined Thread:  ${Thread.currentThread().name}")   //  this coroutine will run in thread `worker2`
            }
        }

//        GlobalScope.launch(Dispatchers.Unconfined) {
//            //  not confined to any thread, it'll run in `main` thread
//            println("yup: I'm CoRoutine that runs in UnConfined Thread:  ${Thread.currentThread().name}")
//        }

        GlobalScope.launch(newSingleThreadContext("coroutine will work in this thread!")) {
            println("yup: I'm CoRoutine that runs in specified Thread:  ${Thread.currentThread().name}")
        }

        //  network call simulation
        GlobalScope.launch(Dispatchers.IO) {
            println("yup: sim n/w call I'm CoRoutine that runs in worker Thread:  ${Thread.currentThread().name}")
            val resp = doNetworkCall1()
            withContext(Dispatchers.Main) {
                println("yup: sim n/w call I'm CoRoutine that runs in main Thread:  ${Thread.currentThread().name}")
                tvDummy.text = resp
            }
        }
    }

    private fun suspendFunc2() {
        GlobalScope.launch {
            val resp1 = doNetworkCall1()
            val resp2 = doNetworkCall2()
            println("yup res resp1: $resp1")
            println("yup res resp2: $resp2")
        }
    }

    private suspend fun doNetworkCall1(): String {
        delay(3000L)
        return "this is resp1"
    }

    private suspend fun doNetworkCall2(): String {
        delay(3000L)
        return "this is resp2"
    }


    private fun basicCoroutine1() {
        /*
        * O/P
        *
        * 2020-09-15 23:00:56.531 11965-11965/com.example.croutinesdemo I/System.out: yup hello from main
          2020-09-15 23:00:59.538 11965-12004/com.example.croutinesdemo I/System.out: yup hello from  DefaultDispatcher-worker-1
        * */
        GlobalScope.launch {    //  launches co routine, that lives for whole application life time
            delay(3000L)
            println("yup hello from  ${Thread.currentThread().name}")
        }
    }
}

SecondActivity.kt

package com.example.croutinesdemo

import androidx.appcompat.app.AppCompatActivity

class SecondActivity : AppCompatActivity()