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[WIP] Introducing coroutine-debug module with probe-based agent
 * Agent automatically captures stacktrace when coroutine is created * Agent patches coroutine completion, so backtrace augmentation (#493) prepends creation stacktrace to the augmented stacktrace * Agent can be dynamically loaded and unloaded Fixes #74
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‎core/kotlinx-coroutines-debug/build.gradle

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/*
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* Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
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*/
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dependencies {
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compile "net.bytebuddy:byte-buddy:$byte_buddy_version"
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compile "net.bytebuddy:byte-buddy-agent:$byte_buddy_version"
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}

‎core/kotlinx-coroutines-debug/src/DebugProbes.kt

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/*
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* Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
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*/
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@file:Suppress("unused")
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package kotlinx.coroutines
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import kotlinx.coroutines.internal.*
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import kotlinx.coroutines.internal.CoroutineStackFrame
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import net.bytebuddy.*
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import net.bytebuddy.agent.*
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import net.bytebuddy.dynamic.loading.*
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import java.lang.management.*
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import java.util.*
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import kotlin.collections.ArrayList
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import kotlin.coroutines.*
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/**
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* Debug probes support.
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*
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* Debug probes is a dynamic attach mechanism, which installs multiple hooks into [Continuation] machinery.
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* It significantly slows down all coroutine-related code, but in return provides a lot of debug information, including
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* asynchronous stack-traces and coroutine dumps (similar to [ThreadMXBean.dumpAllThreads] and `jstack`.
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*
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* Installed hooks:
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*
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* * `probeCoroutineResumed` is invoked on every [Continuation.resume].
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* * `probeCoroutineSuspended` is invoked on every continuation suspension.
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* * `probeCoroutineCreated` is invoked on every coroutine creation using stdlib intrinsics.
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*
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* Overhead:
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* * Every created continuation is stored in a weak hash map, thus adding additional GC pressure
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* * On every created continuation, stacktrace of the current thread is dumped
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* * On every `resume` and `suspend`, [WeakHashMap] is updated under a global lock
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*
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* **WARNING: DO NOT USE DEBUG PROBES IN PRODUCTION ENVIRONMENT**
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*/
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public object DebugProbes {
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private val traces = WeakHashMap<Continuation<*>, Array<StackTraceElement>>()
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private var installed: Boolean = false
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/**
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* Installs a [DebugProbes] instead of no-op stdlib probes by redefining
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* debug probes class using the same class loader.
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*
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* **WARNING: DO NOT USE DEBUG PROBES IN PRODUCTION ENVIRONMENT**
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* Subsequent invocations of this method have no effect.
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*/
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@Synchronized
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public fun install() {
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if (installed) {
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return
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}
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installed = true
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ByteBuddyAgent.install()
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val cl = Class.forName("kotlin.coroutines.jvm.internal.DebugProbesKt")
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val cl2 = Class.forName("kotlinx.coroutines.DebugProbesKt")
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ByteBuddy()
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.redefine(cl2)
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.name(cl.name)
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.make()
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.load(cl.classLoader, ClassReloadingStrategy.fromInstalledAgent())
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}
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/**
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* Uninstall debug probes
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*/
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@Synchronized
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public fun uninstall() {
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if (!installed) {
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return
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}
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traces.clear()
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ByteBuddyAgent.install()
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val cl = Class.forName("kotlin.coroutines.jvm.internal.DebugProbesKt")
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val cl2 = Class.forName("kotlinx.coroutines.NoOpProbesKt")
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ByteBuddy()
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.redefine(cl2)
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.name(cl.name)
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.make()
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.load(cl.classLoader, ClassReloadingStrategy.fromInstalledAgent())
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}
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/**
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* Invokes given block of code with installed debug probes and unistall probes in the end.
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* **NOTE:** this method is not composable, it will uninstall debug probes even if they were installed
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* prior to method invocation
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*/
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public inline fun withDebugProbes(block: () -> Unit) {
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install()
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try {
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block()
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} finally {
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uninstall()
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}
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}
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public fun dumpCoroutines(): String = TODO("Not implemented")
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@Synchronized
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internal fun probeCoroutineResumed(frame: Continuation<*>) {
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}
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@Synchronized
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internal fun probeCoroutineSuspended(frame: Continuation<*>) {
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}
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@Synchronized
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internal fun <T> probeCoroutineCreated(completion: kotlin.coroutines.Continuation<T>): kotlin.coroutines.Continuation<T> {
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val stacktrace = sanitizedStackTrace(Exception())
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traces[completion] = stacktrace
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// TODO create lazy proxy and reverse stacktrace on demand
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val frames = ArrayList<CoroutineStackFrame?>(stacktrace.size)
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for ((index, frame) in stacktrace.reversed().withIndex()) {
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frames += object : CoroutineStackFrame {
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override val callerFrame: CoroutineStackFrame?
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get() = if (index == 0) null else frames[index - 1]
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override fun getStackTraceElement(): StackTraceElement = frame
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}
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}
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return object : Continuation<T> by completion, CoroutineStackFrame by frames.last()!! {}
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}
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private fun <T : Throwable> sanitizedStackTrace(throwable: T): Array<StackTraceElement> {
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val stackTrace = throwable.stackTrace
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val size = stackTrace.size
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var lastIntrinsic = -1
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for (i in 0 until size) {
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val name = stackTrace[i].className
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if ("kotlin.coroutines.jvm.internal.DebugProbesKt" == name) {
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lastIntrinsic = i
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}
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}
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val startIndex = lastIntrinsic + 1
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return Array(size - lastIntrinsic) {
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if (it == 0) {
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artificialFrame("Coroutine creation callsite")
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} else {
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stackTrace[startIndex + it - 1]
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}
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}
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}
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}
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// Stubs which are injected as coroutine probes. Require direct match of signatures
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internal fun probeCoroutineResumed(frame: Continuation<*>) = DebugProbes.probeCoroutineResumed(frame)
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internal fun probeCoroutineSuspended(frame: Continuation<*>) = DebugProbes.probeCoroutineSuspended(frame)
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internal fun <T> probeCoroutineCreated(completion: kotlin.coroutines.Continuation<T>): kotlin.coroutines.Continuation<T> =
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DebugProbes.probeCoroutineCreated(completion)

‎core/kotlinx-coroutines-debug/src/NoOpProbes.kt

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/*
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* Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
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*/
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@file:Suppress("unused")
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package kotlinx.coroutines
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import kotlin.coroutines.*
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@JvmName("probeCoroutineResumed")
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internal fun probeCoroutineResumedNoOp(frame: Continuation<*>) = Unit
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@JvmName("probeCoroutineSuspended")
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internal fun probeCoroutineSuspendedNoOp(frame: Continuation<*>) = Unit
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@JvmName("probeCoroutineCreated")
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internal fun <T> probeCoroutineCreatedNoOp(completion: kotlin.coroutines.Continuation<T>): kotlin.coroutines.Continuation<T> = completion

‎core/kotlinx-coroutines-debug/test/DebugProbesTest.kt

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/*
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* Copyright 2016-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
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*/
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package kotlinx.coroutines
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import org.junit.Test
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import java.io.*
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import java.util.concurrent.*
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import kotlin.test.*
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class DebugProbesTest : TestBase() {
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private fun CoroutineScope.createDeferred(): Deferred<*> = async {
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throw ExecutionException(null)
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}
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@Test
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fun testAsync() = runTest {
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val deferred = createDeferred()
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val traces = listOf(
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"java.util.concurrent.ExecutionException\n" +
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"\t(Current coroutine stacktrace)\n" +
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"\tat kotlinx/coroutines/DeferredCoroutine.await\$suspendImpl(Deferred.kt:234)\n" +
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"\tat kotlinx/coroutines/DebugProbesTest.oneMoreNestedMethod(DebugProbesTest.kt:49)\n" +
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"\tat kotlinx/coroutines/DebugProbesTest.nestedMethod(DebugProbesTest.kt:44)\n" +
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"\tat kotlinx/coroutines/DebugProbesTest\$testAsync\$1.invokeSuspend(DebugProbesTest.kt:17)\n" +
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"Caused by: java.util.concurrent.ExecutionException\n" +
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"\tat kotlinx.coroutines.DebugProbesTest\$createDeferred\$1.invokeSuspend(DebugProbesTest.kt:16)\n" +
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"\tat kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:32)\n"
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)
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nestedMethod(deferred, traces)
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deferred.join()
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}
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@Test
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fun testAsyncWithProbes() = DebugProbes.withDebugProbes {
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runTest {
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val deferred = createDeferred()
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val traces = listOf(
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"java.util.concurrent.ExecutionException\n" +
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"\t(Current coroutine stacktrace)\n" +
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"\tat kotlinx/coroutines/DeferredCoroutine.await\$suspendImpl(Deferred.kt:234)\n" +
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"\tat kotlinx/coroutines/DebugProbesTest.oneMoreNestedMethod(DebugProbesTest.kt:71)\n" +
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"\tat kotlinx/coroutines/DebugProbesTest.nestedMethod(DebugProbesTest.kt:66)\n" +
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"\tat kotlinx/coroutines/DebugProbesTest\$testAsyncWithProbes\$1\$1.invokeSuspend(DebugProbesTest.kt:43)\n" +
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"\t(Coroutine creation callsite)\n" +
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"\tat kotlin.coroutines.intrinsics.IntrinsicsKt__IntrinsicsJvmKt.createCoroutineUnintercepted(IntrinsicsJvm.kt:116)\n" +
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"\tat kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:23)\n" +
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"\tat kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:99)\n" +
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"\tat kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:148)\n" +
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"\tat kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:45)\n" +
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"\tat kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)\n" +
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"\tat kotlinx.coroutines.TestBase.runTest(TestBase.kt:138)\n" +
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"\tat kotlinx.coroutines.TestBase.runTest\$default(TestBase.kt:19)\n" +
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"\tat kotlinx.coroutines.DebugProbesTest.testAsyncWithProbes(DebugProbesTest.kt:38)",
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"Caused by: java.util.concurrent.ExecutionException\n" +
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"\tat kotlinx.coroutines.DebugProbesTest\$createDeferred\$1.invokeSuspend(DebugProbesTest.kt:16)\n" +
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"\tat kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:32)\n")
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nestedMethod(deferred, traces)
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deferred.join()
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}
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}
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private suspend fun nestedMethod(deferred: Deferred<*>, traces: List<String>) {
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oneMoreNestedMethod(deferred, traces)
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assertTrue(true) // Prevent tail-call optimization
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}
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private suspend fun oneMoreNestedMethod(deferred: Deferred<*>, traces: List<String>) {
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try {
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deferred.await()
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expectUnreached()
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} catch (e: ExecutionException) {
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verifyStackTrace(e, traces)
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}
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}
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private fun verifyStackTrace(e: Throwable, traces: List<String>) {
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val stacktrace = toStackTrace(e)
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traces.forEach {
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assertTrue(stacktrace.trimStackTrace().contains(it.trimStackTrace()),
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"\nExpected trace element:\n$it\n\nActual stacktrace:\n$stacktrace")
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}
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val causes = stacktrace.count("Caused by")
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assertNotEquals(0, causes)
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assertEquals(causes, traces.map { it.count("Caused by") }.sum())
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}
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private fun toStackTrace(t: Throwable): String {
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val sw = StringWriter() as Writer
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t.printStackTrace(PrintWriter(sw))
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return sw.toString()
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}
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private fun String.trimStackTrace(): String {
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return applyBackspace(trimIndent().replace(Regex(":[0-9]+"), ""))
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}
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private fun applyBackspace(line: String): String {
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val array = line.toCharArray()
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val stack = CharArray(array.size)
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var stackSize = -1
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for (c in array) {
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if (c != '\b') {
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stack[++stackSize] = c
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} else {
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--stackSize
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}
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}
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return String(stack, 0, stackSize)
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}
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private fun String.count(substring: String): Int = split(substring).size - 1
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}

‎gradle.properties

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# Kotlin
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version=0.26.0-rc13-SNAPSHOT
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version=0.26.0-rc13
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group=org.jetbrains.kotlinx
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kotlin_version=1.3.0-rc-6
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kotlin_native_version=0.9
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# Dependencies
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junit_version=4.12
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atomicFU_version=0.11.6
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byte_buddy_version=1.8.22
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html_version=0.6.8
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lincheck_version=1.9
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dokka_version=0.9.16-rdev-2-mpp-hacks

‎settings.gradle

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module('common/kotlinx-coroutines-core-common')
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module('core/kotlinx-coroutines-core')
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module('core/kotlinx-coroutines-debug')
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module('integration/kotlinx-coroutines-guava')
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module('integration/kotlinx-coroutines-jdk8')
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module('js/example-frontend-js')
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module('native/kotlinx-coroutines-core-native')
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