Add playground files for Structured concurrency

Author: LukasLechnerDev

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/playground/structuredconcurrency/1_coroutines_need_to_be_started_in_scope.kt

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+package com.lukaslechner.coroutineusecasesonandroid.playground.structuredconcurrency
+
+import kotlinx.coroutines.*
+
+val scope = CoroutineScope(Dispatchers.Default)
+
+fun main() = runBlocking<Unit> {
+
+    val job = scope.launch {
+        delay(100)
+        println("Coroutine completed")
+    }
+
+    job.invokeOnCompletion { throwable ->
+        if (throwable is CancellationException) {
+            println("Coroutine was cancelled")
+        }
+    }
+
+    delay(50)
+    onDestroy()
+}
+
+fun onDestroy() {
+    println("life-time of scope ends")
+    scope.cancel()
+}

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/playground/structuredconcurrency/2_job_hierarchy.kt

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+package com.lukaslechner.coroutineusecasesonandroid.playground.structuredconcurrency
+
+import kotlinx.coroutines.*
+
+fun main() {
+
+    val scopeJob = Job()
+    val scope = CoroutineScope(Dispatchers.Default + scopeJob)
+
+    val passedJob = Job()
+    val coroutineJob = scope.launch(passedJob) {
+        println("Starting coroutine")
+        delay(1000)
+    }
+
+    println("passedJob and coroutineJob are references to the same job object: ${passedJob === coroutineJob}")
+
+    println("Is coroutineJob a child of scopeJob? =>${scopeJob.children.contains(coroutineJob)}")
+}

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/playground/structuredconcurrency/3_parents_wait_for_children.kt

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+package com.lukaslechner.coroutineusecasesonandroid.playground.structuredconcurrency
+
+import kotlinx.coroutines.*
+
+fun main() = runBlocking<Unit> {
+
+    val scope = CoroutineScope(Dispatchers.Default)
+
+    val parentCoroutineJob = scope.launch {
+        launch {
+            delay(1000)
+            println("Child Coroutine 1 has completed!")
+        }
+        launch {
+            delay(1000)
+            println("Child Coroutine 2 has completed!")
+        }
+    }
+
+    parentCoroutineJob.join()
+    println("Parent Coroutine has completed!")
+}

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/playground/structuredconcurrency/4_cancelling_parents_and_children.kt

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+package com.lukaslechner.coroutineusecasesonandroid.playground.structuredconcurrency
+
+import kotlinx.coroutines.*
+
+fun main() = runBlocking<Unit> {
+
+    val scope = CoroutineScope(Dispatchers.Default)
+
+    scope.coroutineContext[Job]!!.invokeOnCompletion { throwable ->
+        if (throwable is CancellationException) {
+            println("Parent job was cancelled")
+        }
+    }
+
+    val childCoroutine1Job = scope.launch {
+        delay(1000)
+        println("Coroutine 1 completed")
+    }
+    childCoroutine1Job.invokeOnCompletion { throwable ->
+        if (throwable is CancellationException) {
+            println("Coroutine 1 was cancelled!")
+        }
+    }
+
+    scope.launch {
+        delay(1000)
+        println("Coroutine 2 completed")
+    }.invokeOnCompletion { throwable ->
+        if (throwable is CancellationException) {
+            println("Coroutine 2 was cancelled!")
+        }
+    }
+
+    delay(200)
+
+    childCoroutine1Job.cancelAndJoin()
+
+    // scope.coroutineContext[Job]!!.cancelAndJoin()
+}

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/playground/structuredconcurrency/5_globalscope.kt

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+package com.lukaslechner.coroutineusecasesonandroid.playground.structuredconcurrency
+
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.launch
+
+fun main() {
+
+    println("Job of GlobalScope: ${GlobalScope.coroutineContext[Job]}")
+
+    GlobalScope.launch {
+
+    }
+
+}