How can I make sure all Kotlin coroutines created by a ktor websocket client are cleared up? - kotlin

Question

I'm trying to wrap my head around Kotlin coroutines and Ktors websocket support. My understanding is that runBlocking will create a scope and that it will block as long as there are coroutines living inside that scope (or child scopes), but I when the call to runBlocking in the test below returns there are still two coroutines alive..
Why am I leaking coroutines here?
package dummy
import io.ktor.client.HttpClient
import io.ktor.client.features.websocket.WebSockets
import io.ktor.client.features.websocket.wss
import io.ktor.http.HttpMethod
import io.ktor.http.cio.websocket.Frame
import io.ktor.http.cio.websocket.readBytes
import io.ktor.http.cio.websocket.readText
import io.ktor.util.KtorExperimentalAPI
import kotlinx.coroutines.*
import kotlinx.coroutines.debug.DebugProbes
import org.junit.jupiter.api.Assertions
import org.junit.jupiter.api.Test
#ExperimentalCoroutinesApi
#KtorExperimentalAPI
class WebsocketTest {
#Test
fun tidy() {
DebugProbes.install()
runBlocking {
val socketJob = Job()
launch(CoroutineName("Websocket") + socketJob) {
println("Connecting to websocket")
connectWebsocket(socketJob)
println("Websocket dead?")
}
launch(CoroutineName("Ninja socket killer")) {
delay(3500)
println("Killing websocket client")
socketJob.cancel(message = "Time to die..")
}
}
println("\n\n-------")
DebugProbes.dumpCoroutines(System.err)
Assertions.assertEquals(0, DebugProbes.dumpCoroutinesInfo().size, "It would be nice if all coroutines had been cleared up by now..")
}
}
#KtorExperimentalAPI
private suspend fun connectWebsocket(socketJob: CompletableJob) {
val client = HttpClient {
install(WebSockets)
}
socketJob.invokeOnCompletion {
println("Shutting down ktor http client")
client.close()
}
client.wss(
method = HttpMethod.Get,
host = "echo.websocket.org",
port = 443,
path = "/"
) {
send(Frame.Text("Hello World"))
for (frame in incoming) {
when (frame) {
is Frame.Text -> println(frame.readText())
is Frame.Binary -> println(frame.readBytes())
}
delay(1000)
send(Frame.Text("Hello World"))
}
}
}
build.gradle.kts
import org.gradle.api.tasks.testing.logging.TestExceptionFormat
import org.gradle.api.tasks.testing.logging.TestLogEvent
plugins {
kotlin("jvm") version "1.3.41" apply true
}
repositories {
mavenCentral()
}
val ktorVersion = "1.2.3"
val junitVersion = "5.5.1"
dependencies {
implementation(kotlin("stdlib-jdk8"))
implementation("io.ktor:ktor-client-websockets:$ktorVersion")
implementation("io.ktor:ktor-client-okhttp:$ktorVersion")
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-debug:1.3.0-RC2")
testImplementation("org.junit.jupiter:junit-jupiter-api:$junitVersion")
testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:$junitVersion")
}
tasks.withType<Test> {
useJUnitPlatform()
testLogging {
showExceptions = true
showStackTraces = true
exceptionFormat = TestExceptionFormat.FULL
events = setOf(TestLogEvent.PASSED, TestLogEvent.SKIPPED, TestLogEvent.FAILED)
}
}

Answer 1

Seems like I have figured it out (obviously just after ripping my hair out long enough to make this post in the first place). When I wrote the post I leaked two coroutines and one of them "solved itself" (I'm not very happy about that, but what ever I do I can't reproduce it).
The second coroutine leaked because Nonce.kt from Ktor explicitly launches a coroutine in GlobalScope.
https://github.com/ktorio/ktor/blob/master/ktor-utils/jvm/src/io/ktor/util/Nonce.kt#L30
private val nonceGeneratorJob =
GlobalScope.launch(
context = Dispatchers.IO + NonCancellable + NonceGeneratorCoroutineName,
start = CoroutineStart.LAZY
) { ....