kotlin-hands-on / intro-coroutines

Introduction to Coroutines and Channels Hands-On Lab

This repository is the code corresponding to the Introduction to Coroutines and Channels Hands-On Lab.

intro-coroutines's Issues

ConcurrentTest fails with 'This job has not completed yet'

Request5ConcurrentKtTest.kt fails for me with:

java.lang.IllegalStateException: This job has not completed yet

Maybe this gets fixed once

• Kotlin/kotlinx.coroutines#1206 is merged
  and
• Kotlin/kotlinx.coroutines#1204 is fixed and rolled out

kotlin version used: 1.3.41

Discrepencies between doc and code

https://github.com/kotlin-hands-on/intro-coroutines/blob/solutions/src/tasks/Request5Concurrent.kt .
and
https://play.kotlinlang.org/hands-on/Introduction%20to%20Coroutines%20and%20Channels/05_Concurrency (section solution)

The documentation does not have service as a parameter, code and solution do.

It seems that all the chapters of the documentation have the same issue.

Request9RxProgressKtTest is failing in 'rx' branch

In the rx branch, Request9RxProgressKtTest is failing due to AssertionError.

It seems the test is failing due to the improvement made in loadContributorsReactiveProgress function by using Observable.scan() function instead of Observable.map() as highlighted below:

return repoUsers
        .scan(listOf()) { allUsers, users ->
            (allUsers + users).aggregate()
        }

The problem here is scan() function emits the initialValue while subscribing, in this case, empty list and hence the test assertion is failing.

There are two ways to solve this:

1. Go back t use map() instead of scan()
2. Apply filter() to filter out the empty list after scan()

I think the second one is kind of confusing, so can go ahead with first. Thoughts?

[Question] - RxJava performance verses coroutines

I've noticed that the fastest coroutine variant runs in a ~5.6 seconds
however, the RxJava variant runs in ~2 seconds,

If I understand correctly,
RxJava runs every request on a different thread and holds it while the coroutine uses a looper to schedule all of the io on the same thread, saving space.

I've tried achieving better performance on coroutines to be in par with RxJava but failed,

can you better explain that? it seems to me that the RxJava variant is much better because of that (for time optimization).

Correct method names

In contributors.MockGithubService in comment section it needs Call to be appended to the end of each method. I cant push branch with such fix :(
@svtk

AWTError

I am unable to pinpoint the problem here but after importing the project into IntelliJ from GitHub I am running into the following error on execution of src/contributors/main/kt

Exception in thread "main" java.awt.AWTError: Assistive Technology not found: org.GNOME.Accessibility.AtkWrapper
	at java.awt.Toolkit.loadAssistiveTechnologies(Toolkit.java:807)
	at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:886)
	at sun.swing.SwingUtilities2.getSystemMnemonicKeyMask(SwingUtilities2.java:2032)
	at javax.swing.plaf.basic.BasicLookAndFeel.initComponentDefaults(BasicLookAndFeel.java:1158)
	at javax.swing.plaf.metal.MetalLookAndFeel.initComponentDefaults(MetalLookAndFeel.java:431)
	at javax.swing.plaf.basic.BasicLookAndFeel.getDefaults(BasicLookAndFeel.java:148)
	at javax.swing.plaf.metal.MetalLookAndFeel.getDefaults(MetalLookAndFeel.java:1577)
	at javax.swing.UIManager.setLookAndFeel(UIManager.java:539)
	at javax.swing.UIManager.setLookAndFeel(UIManager.java:579)
	at javax.swing.UIManager.initializeDefaultLAF(UIManager.java:1349)
	at javax.swing.UIManager.initialize(UIManager.java:1459)
	at javax.swing.UIManager.maybeInitialize(UIManager.java:1426)
	at javax.swing.UIManager.getLookAndFeelDefaults(UIManager.java:1037)
	at contributors.ContributorsUIKt.setDefaultFontSize(ContributorsUI.kt:147)
	at contributors.MainKt.main(main.kt:4)
	at contributors.MainKt.main(main.kt)

Thanks in advance.

Only blocking and background variant works well

Only blocking and background variant works well

Version 'Suspend' raises illegal reflective access / AWT-EventQueue-0" kotlin.NotImplementedError

90 [AWT-EventQueue-0] INFO Contributors - Clearing result
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by retrofit2.Platform (file:/C:/Users/Gunnar/.gradle/caches/modules-2/files-2.1/com.squareup.retrofit2/retrofit/2.9.0/d8fdfbd5da952141a665a403348b74538efc05ff/retrofit-2.9.0.jar) to constructor java.lang.invoke.MethodHandles$Lookup(java.lang.Class,int)
WARNING: Please consider reporting this to the maintainers of retrofit2.Platform
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Exception in thread "AWT-EventQueue-0" kotlin.NotImplementedError: An operation is not implemented.
at tasks.Request4SuspendKt.loadContributorsSuspend(Request4Suspend.kt:6)
at contributors.Contributors$loadContributors$3.invokeSuspend(Contributors.kt:77)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:313)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

started with:
"C:\Program Files\OpenJDK11\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition Eval\lib\idea_rt.jar=64163:C:\Program Files\JetBrains\IntelliJ IDEA Community Edition Eval\bin" -Dfile.encoding=UTF-8 -classpath "C:\Development\Travelling Salesman\GitHub\KotlinIntroCoroutines\build\classes\kotlin\main;C:\Development\Travelling Salesman\GitHub\KotlinIntroCoroutines\build\resources\main;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-reflect\1.5.20\63810951f09a27f7827977f1bc21094042a915e\kotlin-reflect-1.5.20.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\com.jakewharton.retrofit\retrofit2-kotlinx-serialization-converter\0.8.0\4fe25acf1b2f12f17d7187f7cfcf4ee730822d50\retrofit2-kotlinx-serialization-converter-0.8.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\com.squareup.retrofit2\retrofit-mock\2.9.0\da17c2bcd6a771694ce79091d8394a3118bd7890\retrofit-mock-2.9.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\com.squareup.retrofit2\adapter-rxjava2\2.9.0\180ad7353dbf0480cabc215948b5a234e3692f0a\adapter-rxjava2-2.9.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\com.squareup.retrofit2\retrofit\2.9.0\d8fdfbd5da952141a665a403348b74538efc05ff\retrofit-2.9.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\com.squareup.okhttp3\okhttp\4.9.1\51215279c3fe472c59b6b7dd7491e6ac2e28a81b\okhttp-4.9.1.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-coroutines-swing\1.5.1\3a6498130368bbd3a5cdbb15264e64cedac80eb5\kotlinx-coroutines-swing-1.5.1.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-coroutines-jdk8\1.5.1\6a30b64389d2f541d27c7756d414412eb52a15d\kotlinx-coroutines-jdk8-1.5.1.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-coroutines-slf4j\1.5.1\df3c9da192aa8c14da5f1b81e0c39e8fb646cc10\kotlinx-coroutines-slf4j-1.5.1.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib\1.5.20\9de35cc611bcecec8edce1d56d8e659953806751\kotlin-stdlib-1.5.20.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-coroutines-debug\1.5.1\f0e934de961d0d36f3fb9c61114ddf8803abbcde\kotlinx-coroutines-debug-1.5.1.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\ch.qos.logback\logback-classic\1.2.3\7c4f3c474fb2c041d8028740440937705ebb473a\logback-classic-1.2.3.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\io.reactivex.rxjava2\rxkotlin\2.4.0\2f4a35d683b4851a036b8828d4a7c6888adf75c7\rxkotlin-2.4.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\io.reactivex.rxjava2\rxjava\2.2.21\6f13f24c44567fc660aab94d639cda9f0fe95628\rxjava-2.2.21.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-serialization-core-jvm\1.2.2\f1facb8403cacd65ee314f91fec216ba229f9ac2\kotlinx-serialization-core-jvm-1.2.2.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.reactivestreams\reactive-streams\1.0.3\d9fb7a7926ffa635b3dcaa5049fb2bfa25b3e7d0\reactive-streams-1.0.3.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\com.squareup.okio\okio\2.8.0\49b64e09d81c0cc84b267edd0c2fd7df5a64c78c\okio-jvm-2.8.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-serialization-json-jvm\1.2.2\7cd520a077c5d1addfa8f80f39cd14cb2de027d7\kotlinx-serialization-json-jvm-1.2.2.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib-jdk8\1.5.20\636c5653641cd956de9aee5792155b07ea49825e\kotlin-stdlib-jdk8-1.5.20.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.slf4j\slf4j-api\1.7.25\da76ca59f6a57ee3102f8f9bd9cee742973efa8a\slf4j-api-1.7.25.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlinx\kotlinx-coroutines-core-jvm\1.5.1\59d09c330d2977b39e1e4c0e3711fc903e1b46b0\kotlinx-coroutines-core-jvm-1.5.1.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains\annotations\13.0\919f0dfe192fb4e063e7dacadee7f8bb9a2672a9\annotations-13.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib-common\1.5.20\3d79dbd48bf605f4aac1e7028981a1953e245cbb\kotlin-stdlib-common-1.5.20.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\ch.qos.logback\logback-core\1.2.3\864344400c3d4d92dfeb0a305dc87d953677c03c\logback-core-1.2.3.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\org.jetbrains.kotlin\kotlin-stdlib-jdk7\1.5.20\218b60e1d446d1e0a18bc7aa8663634b136fbcc5\kotlin-stdlib-jdk7-1.5.20.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\net.java.dev.jna\jna-platform\5.5.0\af38e7c4d0fc73c23ecd785443705bfdee5b90bf\jna-platform-5.5.0.jar;C:\Users\Gunnar.gradle\caches\modules-2\files-2.1\net.java.dev.jna\jna\5.5.0\e0845217c4907822403912ad6828d8e0b256208\jna-5.5.0.jar" contributors.MainKt

Sorting is not stable enough

Request6ProgressKtTest.testProgress failed with this:

Wrong intermediate result after 3200: expected:<[User(login=user-2, contributions=50), User(login=user-1, contributions=50)]> but was:<[User(login=user-1, contributions=50), User(login=user-2, contributions=50)]>
Expected :[User(login=user-2, contributions=50), User(login=user-1, contributions=50)]
Actual   :[User(login=user-1, contributions=50), User(login=user-2, contributions=50)]

intro-coroutines/src/tasks/Aggregation.kt

Line 20 in c51a403

.sortedByDescending { it.contributions }

(in the solution branch) should be updated to

        .sortedWith(compareByDescending<User> { it.contributions }
            .thenByDescending { it.login })

This is my solution for Request6Progress.kt:

suspend fun loadContributorsProgress(
    service: GitHubService,
    req: RequestData,
    updateResults: suspend (List<User>, completed: Boolean) -> Unit
) {
    val repos = service
        .getOrgRepos(req.org)
        .also { logRepos(req, it) }
        .body() ?: listOf()

    var allUsers = emptyList<User>()
    repos.forEachIndexed { index, repo ->
        val users = service
            .getRepoContributors(req.org, repo.name)
            .also { logUsers(repo, it) }
            .bodyList()
        allUsers += users
        // allUsers = (allUsers + users).aggregate() // uncomment this line to make the test happy
        updateResults(allUsers.aggregate(), index == repos.lastIndex)
    }
}

Suggested solutions for Request3Callbacks don't handle errors

As far as I understand the current revision of Using callbacks suggests that using CountDownLatch is the best approach to solve the problem.

However, the provided solution doesn't work even if one of the requests fails. When a request fails, the error is simply logged on Request3Callbacks.kt#L34. countDown() isn't called in that case. Because of that, the thread will never return from await() call.

The same goes for the second suggested solution (AtomicInteger). The counter isn't incremented if a request fails. Because of that, when all requests are completed, the counter won't be equal to the count of repositories.

I am not sure if this should be fixed or even mentioned in the docs, but I think it should be at least listed as a known issue.

.apply() is deprecated in the new Kotlin version

Dear JetBrains

.apply() seems to be deprecated and I have problems running the app in Intellij since I can't find the main class.

cloning the project and running main method does nothing

I cloned the project and run the main method in contributors/main.kt. Nothing happens. Seems like some plugin is missing. But how do I add that?

Tests build fail

Branch: master

Expected behavior:
Tests to build successfully.

Actual behavior:
Tests fail to build because of MockGithubService#getOrgRepos(org: String) and MockGithubService#getRepoContributors(owner: String, repo: String)

building fails with org.jetbrains.kotlin.jvm plugin not found

Just cloned it and run gradle build:
Build file '/Users/adrianalbu/Downloads/intro-coroutines/build.gradle' line: 2

Plugin [id: 'org.jetbrains.kotlin.jvm', version: '1.5.20'] was not found in any of the following sources:

• Try:
  Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Exception is:
  org.gradle.api.plugins.UnknownPluginException: Plugin [id: 'org.jetbrains.kotlin.jvm', version: '1.5.20'] was not found in any of the following sources:

• Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
• Plugin Repositories (could not resolve plugin artifact 'org.jetbrains.kotlin.jvm:org.jetbrains.kotlin.jvm.gradle.plugin:1.5.20')
  Searched in the following repositories:
  Gradle Central Plugin Repository
  at org.gradle.plugin.use.internal.DefaultPluginRequestApplicator.resolveToFoundResult(DefaultPluginRequestApplicator.java:213)
  at org.gradle.plugin.use.internal.DefaultPluginRequestApplicator.lambda$resolvePluginRequests$4(DefaultPluginRequestApplicator.java:146)
  at org.gradle.util.CollectionUtils.collect(CollectionUtils.java:207)
  at org.gradle.util.CollectionUtils.collect(CollectionUtils.java:201)
  at org.gradle.plugin.use.internal.DefaultPluginRequestApplicator.resolvePluginRequests(DefaultPluginRequestApplicator.java:144)
  at org.gradle.plugin.use.internal.DefaultPluginRequestApplicator.applyPlugins(DefaultPluginRequestApplicator.java:84)
  at org.gradle.configuration.DefaultScriptPluginFactory$ScriptPluginImpl.apply(DefaultScriptPluginFactory.java:117)
  at org.gradle.configuration.BuildOperationScriptPlugin$1.run(BuildOperationScriptPlugin.java:65)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:29)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:26)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:75)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:153)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.run(DefaultBuildOperationRunner.java:56)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.lambda$run$1(DefaultBuildOperationExecutor.java:71)
  at org.gradle.internal.operations.UnmanagedBuildOperationWrapper.runWithUnmanagedSupport(UnmanagedBuildOperationWrapper.java:45)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:71)
  at org.gradle.configuration.BuildOperationScriptPlugin.lambda$apply$0(BuildOperationScriptPlugin.java:62)
  at org.gradle.configuration.internal.DefaultUserCodeApplicationContext.apply(DefaultUserCodeApplicationContext.java:43)
  at org.gradle.configuration.BuildOperationScriptPlugin.apply(BuildOperationScriptPlugin.java:62)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.lambda$applyToMutableState$0(DefaultProjectStateRegistry.java:248)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.fromMutableState(DefaultProjectStateRegistry.java:275)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.applyToMutableState(DefaultProjectStateRegistry.java:247)
  at org.gradle.configuration.project.BuildScriptProcessor.execute(BuildScriptProcessor.java:42)
  at org.gradle.configuration.project.BuildScriptProcessor.execute(BuildScriptProcessor.java:26)
  at org.gradle.configuration.project.ConfigureActionsProjectEvaluator.evaluate(ConfigureActionsProjectEvaluator.java:35)
  at org.gradle.configuration.project.LifecycleProjectEvaluator$EvaluateProject.lambda$run$0(LifecycleProjectEvaluator.java:100)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.lambda$applyToMutableState$0(DefaultProjectStateRegistry.java:248)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.lambda$withProjectLock$3(DefaultProjectStateRegistry.java:308)
  at org.gradle.internal.work.DefaultWorkerLeaseService.withLocks(DefaultWorkerLeaseService.java:178)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.withProjectLock(DefaultProjectStateRegistry.java:308)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.fromMutableState(DefaultProjectStateRegistry.java:289)
  at org.gradle.api.internal.project.DefaultProjectStateRegistry$ProjectStateImpl.applyToMutableState(DefaultProjectStateRegistry.java:247)
  at org.gradle.configuration.project.LifecycleProjectEvaluator$EvaluateProject.run(LifecycleProjectEvaluator.java:91)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:29)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:26)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:75)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:153)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.run(DefaultBuildOperationRunner.java:56)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.lambda$run$1(DefaultBuildOperationExecutor.java:71)
  at org.gradle.internal.operations.UnmanagedBuildOperationWrapper.runWithUnmanagedSupport(UnmanagedBuildOperationWrapper.java:45)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:71)
  at org.gradle.configuration.project.LifecycleProjectEvaluator.evaluate(LifecycleProjectEvaluator.java:63)
  at org.gradle.api.internal.project.DefaultProject.evaluate(DefaultProject.java:710)
  at org.gradle.api.internal.project.DefaultProject.evaluate(DefaultProject.java:145)
  at org.gradle.execution.TaskPathProjectEvaluator.configure(TaskPathProjectEvaluator.java:36)
  at org.gradle.execution.TaskPathProjectEvaluator.configureHierarchy(TaskPathProjectEvaluator.java:62)
  at org.gradle.configuration.DefaultProjectsPreparer.prepareProjects(DefaultProjectsPreparer.java:46)
  at org.gradle.configuration.BuildTreePreparingProjectsPreparer.prepareProjects(BuildTreePreparingProjectsPreparer.java:57)
  at org.gradle.configuration.BuildOperationFiringProjectsPreparer$ConfigureBuild.run(BuildOperationFiringProjectsPreparer.java:52)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:29)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:26)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:75)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:153)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.run(DefaultBuildOperationRunner.java:56)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.lambda$run$1(DefaultBuildOperationExecutor.java:71)
  at org.gradle.internal.operations.UnmanagedBuildOperationWrapper.runWithUnmanagedSupport(UnmanagedBuildOperationWrapper.java:45)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:71)
  at org.gradle.configuration.BuildOperationFiringProjectsPreparer.prepareProjects(BuildOperationFiringProjectsPreparer.java:40)
  at org.gradle.initialization.DefaultGradleLauncher.prepareProjects(DefaultGradleLauncher.java:228)
  at org.gradle.initialization.DefaultGradleLauncher.doClassicBuildStages(DefaultGradleLauncher.java:165)
  at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:150)
  at org.gradle.initialization.DefaultGradleLauncher.executeTasks(DefaultGradleLauncher.java:126)
  at org.gradle.internal.invocation.GradleBuildController$1.create(GradleBuildController.java:72)
  at org.gradle.internal.invocation.GradleBuildController$1.create(GradleBuildController.java:67)
  at org.gradle.internal.work.DefaultWorkerLeaseService.withLocks(DefaultWorkerLeaseService.java:178)
  at org.gradle.internal.invocation.GradleBuildController.doBuild(GradleBuildController.java:67)
  at org.gradle.internal.invocation.GradleBuildController.run(GradleBuildController.java:56)
  at org.gradle.tooling.internal.provider.runner.BuildModelActionRunner.run(BuildModelActionRunner.java:54)
  at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35)
  at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35)
  at org.gradle.launcher.exec.BuildOutcomeReportingBuildActionRunner.run(BuildOutcomeReportingBuildActionRunner.java:63)
  at org.gradle.tooling.internal.provider.ValidatingBuildActionRunner.run(ValidatingBuildActionRunner.java:32)
  at org.gradle.tooling.internal.provider.FileSystemWatchingBuildActionRunner.run(FileSystemWatchingBuildActionRunner.java:67)
  at org.gradle.launcher.exec.BuildCompletionNotifyingBuildActionRunner.run(BuildCompletionNotifyingBuildActionRunner.java:41)
  at org.gradle.launcher.exec.RunAsBuildOperationBuildActionRunner$3.call(RunAsBuildOperationBuildActionRunner.java:49)
  at org.gradle.launcher.exec.RunAsBuildOperationBuildActionRunner$3.call(RunAsBuildOperationBuildActionRunner.java:44)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:200)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:195)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:75)
  at org.gradle.internal.operations.DefaultBuildOperationRunner$3.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:153)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:68)
  at org.gradle.internal.operations.DefaultBuildOperationRunner.call(DefaultBuildOperationRunner.java:62)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.lambda$call$2(DefaultBuildOperationExecutor.java:76)
  at org.gradle.internal.operations.UnmanagedBuildOperationWrapper.callWithUnmanagedSupport(UnmanagedBuildOperationWrapper.java:54)
  at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:76)
  at org.gradle.launcher.exec.RunAsBuildOperationBuildActionRunner.run(RunAsBuildOperationBuildActionRunner.java:44)
  at org.gradle.launcher.exec.InProcessBuildActionExecuter.lambda$execute$0(InProcessBuildActionExecuter.java:54)
  at org.gradle.composite.internal.DefaultRootBuildState.run(DefaultRootBuildState.java:87)
  at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:53)
  at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:29)
  at org.gradle.launcher.exec.BuildTreeScopeLifecycleBuildActionExecuter.lambda$execute$0(BuildTreeScopeLifecycleBuildActionExecuter.java:33)
  at org.gradle.internal.buildtree.BuildTreeState.run(BuildTreeState.java:49)
  at org.gradle.launcher.exec.BuildTreeScopeLifecycleBuildActionExecuter.execute(BuildTreeScopeLifecycleBuildActionExecuter.java:32)
  at org.gradle.launcher.exec.BuildTreeScopeLifecycleBuildActionExecuter.execute(BuildTreeScopeLifecycleBuildActionExecuter.java:27)
  at org.gradle.tooling.internal.provider.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:104)
  at org.gradle.tooling.internal.provider.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:55)
  at org.gradle.tooling.internal.provider.SubscribableBuildActionExecuter.execute(SubscribableBuildActionExecuter.java:64)
  at org.gradle.tooling.internal.provider.SubscribableBuildActionExecuter.execute(SubscribableBuildActionExecuter.java:37)
  at org.gradle.tooling.internal.provider.SessionScopeLifecycleBuildActionExecuter.lambda$execute$0(SessionScopeLifecycleBuildActionExecuter.java:54)
  at org.gradle.internal.session.BuildSessionState.run(BuildSessionState.java:67)
  at org.gradle.tooling.internal.provider.SessionScopeLifecycleBuildActionExecuter.execute(SessionScopeLifecycleBuildActionExecuter.java:50)
  at org.gradle.tooling.internal.provider.SessionScopeLifecycleBuildActionExecuter.execute(SessionScopeLifecycleBuildActionExecuter.java:36)
  at org.gradle.tooling.internal.provider.GradleThreadBuildActionExecuter.execute(GradleThreadBuildActionExecuter.java:36)
  at org.gradle.tooling.internal.provider.GradleThreadBuildActionExecuter.execute(GradleThreadBuildActionExecuter.java:25)
  at org.gradle.tooling.internal.provider.StartParamsValidatingActionExecuter.execute(StartParamsValidatingActionExecuter.java:59)
  at org.gradle.tooling.internal.provider.StartParamsValidatingActionExecuter.execute(StartParamsValidatingActionExecuter.java:31)
  at org.gradle.tooling.internal.provider.SessionFailureReportingActionExecuter.execute(SessionFailureReportingActionExecuter.java:55)
  at org.gradle.tooling.internal.provider.SessionFailureReportingActionExecuter.execute(SessionFailureReportingActionExecuter.java:41)
  at org.gradle.tooling.internal.provider.SetupLoggingActionExecuter.execute(SetupLoggingActionExecuter.java:47)
  at org.gradle.tooling.internal.provider.SetupLoggingActionExecuter.execute(SetupLoggingActionExecuter.java:31)
  at org.gradle.launcher.daemon.server.exec.ExecuteBuild.doBuild(ExecuteBuild.java:65)
  at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:37)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.WatchForDisconnection.execute(WatchForDisconnection.java:39)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.ResetDeprecationLogger.execute(ResetDeprecationLogger.java:29)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.RequestStopIfSingleUsedDaemon.execute(RequestStopIfSingleUsedDaemon.java:35)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.ForwardClientInput$2.create(ForwardClientInput.java:78)
  at org.gradle.launcher.daemon.server.exec.ForwardClientInput$2.create(ForwardClientInput.java:75)
  at org.gradle.util.Swapper.swap(Swapper.java:38)
  at org.gradle.launcher.daemon.server.exec.ForwardClientInput.execute(ForwardClientInput.java:75)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.LogAndCheckHealth.execute(LogAndCheckHealth.java:55)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.LogToClient.doBuild(LogToClient.java:63)
  at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:37)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.EstablishBuildEnvironment.doBuild(EstablishBuildEnvironment.java:84)
  at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:37)
  at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:104)
  at org.gradle.launcher.daemon.server.exec.StartBuildOrRespondWithBusy$1.run(StartBuildOrRespondWithBusy.java:52)
  at org.gradle.launcher.daemon.server.DaemonStateCoordinator$1.run(DaemonStateCoordinator.java:297)
  at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
  at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
  at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)

where is solutions branch ?

Kotlin doc says the cloned project will include a 'solutions' branch.
But I see it nowhere.

Use CountDownLatch instead of AtomicInteger

To fix the callback solution I suggest to use a CountDownLatch instead of an AtomicInteger based solution. It won't save LOC but allows for a more decoupled solution (updating the results isn't part of the backend call code):

val countDownLatch = CountDownLatch(repos.size)
for (repo in repos) {
    service.getRepoContributorsCall(req.org, repo.name).onResponse { responseUsers ->
        // more code here
        countDownLatch.countDown()
    }
}

countDownLatch.await()
updateResults(allUsers.aggregate())

Is adding to list thread safe?

In Request3Callbacks.kt you use AtomicInteger to make sure you increment and read the integer in a thread safe way, but you append to the allUsers list which isn't synchronized. Isn't this a problem?

I think it needs a synchronized block

fun loadContributorsCallbacks(service: GitHubService, req: RequestData, updateResults: (List<User>) -> Unit) {
    service.getOrgReposCall(req.org).onResponse { responseRepos ->
        logRepos(req, responseRepos)
        val repos = responseRepos.bodyList()
        val allUsers = mutableListOf<User>()
        var numberOfProcessed = 0
        val lock = Any()
        for (repo in repos) {
            service.getRepoContributorsCall(req.org, repo.name).onResponse { responseUsers ->

                synchronized(lock) {
                    logUsers(repo, responseUsers)
                    val users = responseUsers.bodyList()
                    allUsers += users
                    numberOfProcessed += 1
                    if (numberOfProcessed == repos.size) {
                        updateResults(allUsers.aggregate())
                    }
                }
                
            }
        }
    }
}

Examples should avoid runBlocking? and be more relevant to integration with existing Kotlin project

It has been said to avoid runBlocking and it would never really be used in production code. So, can the examples be more relevant to an existing project where you have Kotlin code and use a new library that has coroutines. Most likely you would not want runBlocking right?

Tutorial text edit suggestion on GlobalScope

Hello 😃

In part of tutorial "Canceling the loading of contributors" on step 3 it is suggested to add 3-second delay.

And the actual code sample stands like that:

suspend fun loadContributorsConcurrent(
    service: GitHubService,
    req: RequestData
): List<User> = coroutineScope {
    // ...
    GlobalScope.async {
        log("starting loading for ${repo.name}")
        delay(3000)
        // load repo contributors
    }
    // ...
}

I guess, it shouldn't be GlobalScope.async {} in this case. Therefore, if we will add GlobalScope, then loading won't be canceled.