Circular Exception delivered to invokeOnCompletion

[FabianFrank]

It seems that Kotlin can create Throwables with circular references. While methods like printStackTrace() tend to handle this well, a lot of logging frameworks crash or go into an infinite loop when encountering these.

Kotlin program:

import kotlinx.coroutines.experimental.launch
import kotlinx.coroutines.experimental.runBlocking


fun main(args: Array<String>) {
    val job = launch {
        println("A")

        launch(coroutineContext) {
            println("B")
            throw RuntimeException("foobar")
        }
    }
    job.invokeOnCompletion {
        it!!.printStackTrace()
    }

    runBlocking {
        job.join()
    }
}

Output:

/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/bin/java "-javaagent:/Applications/IntelliJ IDEA CE.app/Contents/lib/idea_rt.jar=51858:/Applications/IntelliJ IDEA CE.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_162.jdk/Contents/Home/lib/tools.jar:/Users/fabian/projects/coroutinetest/out/production/classes:/Users/fabian/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-jdk8/1.2.31/50094b02ec8a4c2e4444073c722bb56c8a52b83c/kotlin-stdlib-jdk8-1.2.31.jar:/Users/fabian/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlinx/kotlinx-coroutines-core/0.22.5/a654b6962cbdf394cd88e6fc173314c92dd50edb/kotlinx-coroutines-core-0.22.5.jar:/Users/fabian/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib-jdk7/1.2.31/95d6a67e8787280a82a2059e54e4db7ac6cfe74/kotlin-stdlib-jdk7-1.2.31.jar:/Users/fabian/.gradle/caches/modules-2/files-2.1/org.jetbrains.kotlin/kotlin-stdlib/1.2.31/153dcd9ed9db246a7e36f4d7609e2a9f4718c674/kotlin-stdlib-1.2.31.jar:/Users/fabian/.gradle/caches/modules-2/files-2.1/org.jetbrains/annotations/13.0/919f0dfe192fb4e063e7dacadee7f8bb9a2672a9/annotations-13.0.jar MainKt
A
B
Exception in thread "ForkJoinPool.commonPool-worker-2" java.lang.RuntimeException: foobar
	at MainKt$main$job$1$1.doResume(Main.kt:11)
	at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:54)
	at kotlinx.coroutines.experimental.DispatchedTask$DefaultImpls.run(Dispatched.kt:161)
	at kotlinx.coroutines.experimental.DispatchedContinuation.run(Dispatched.kt:25)
	at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
Exception in thread "ForkJoinPool.commonPool-worker-2" java.lang.RuntimeException: foobar
	at MainKt$main$job$1$1.doResume(Main.kt:11)
	at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:54)
	at kotlinx.coroutines.experimental.DispatchedTask$DefaultImpls.run(Dispatched.kt:161)
	at kotlinx.coroutines.experimental.DispatchedContinuation.run(Dispatched.kt:25)
	at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
java.lang.RuntimeException: foobar
	at MainKt$main$job$1$1.doResume(Main.kt:11)
	at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:54)
	at kotlinx.coroutines.experimental.DispatchedTask$DefaultImpls.run(Dispatched.kt:161)
	at kotlinx.coroutines.experimental.DispatchedContinuation.run(Dispatched.kt:25)
	at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
	Suppressed: kotlinx.coroutines.experimental.JobCancellationException: Job is being cancelled; job=StandaloneCoroutine{Cancelled}@44bf0252
		at kotlinx.coroutines.experimental.JobSupport.toCancellationException(Job.kt:788)
		at kotlinx.coroutines.experimental.JobSupport.getCancellationException(Job.kt:778)
		at kotlinx.coroutines.experimental.Child.invoke(Job.kt:1486)
		at kotlinx.coroutines.experimental.JobSupport.notifyCancellation(Job.kt:1534)
		at kotlinx.coroutines.experimental.JobSupport.tryMakeCancelling(Job.kt:1020)
		at kotlinx.coroutines.experimental.JobSupport.makeCancelling(Job.kt:1005)
		at kotlinx.coroutines.experimental.JobSupport.cancel(Job.kt:960)
		at kotlinx.coroutines.experimental.AbstractCoroutine.cancel(AbstractCoroutine.kt:174)
		at kotlinx.coroutines.experimental.CoroutineExceptionHandlerKt.handleCoroutineException(CoroutineExceptionHandler.kt:45)
		at kotlinx.coroutines.experimental.StandaloneCoroutine.onFinishingInternal$kotlinx_coroutines_core(Builders.kt:197)
		at kotlinx.coroutines.experimental.JobSupport.makeCompletingInternal(Job.kt:1083)
		at kotlinx.coroutines.experimental.JobSupport.makeCompletingOnce$kotlinx_coroutines_core(Job.kt:1045)
		at kotlinx.coroutines.experimental.AbstractCoroutine.resumeWithException(AbstractCoroutine.kt:118)
		at kotlin.coroutines.experimental.jvm.internal.CoroutineImpl.resume(CoroutineImpl.kt:53)
		... 7 more
	[CIRCULAR REFERENCE:java.lang.RuntimeException: foobar]

Process finished with exit code 0

[qwwdfsad]

Good catch.
The problem here is that outer launch is cancelled due to inner launch exception, but for its completion handler we'd like to expose original exception from inner launch, thus suppressing JobCancellationException.

As solution we can either try to do something similar to reactor Exception#addThrowable (wrap multiple exceptions into CompositeException) or carefully revisit dependent cancellation paths

[qwwdfsad]

Verified, it crashes logback and it's not going to be fixed: https://jira.qos.ch/browse/LOGBACK-1027

[qwwdfsad]

This specific case was fixed in 0.23 as part of #323

[FabianFrank]

Thank you for shipping a fix! 👍