1# Module kotlinx-coroutines-debug 2 3Debugging facilities for `kotlinx.coroutines` on JVM. 4 5### Overview 6 7This module provides a debug JVM agent that allows to track and trace existing coroutines. 8The main entry point to debug facilities is [DebugProbes] API. 9Call to [DebugProbes.install] installs debug agent via ByteBuddy and starts spying on coroutines when they are created, suspended and resumed. 10 11After that, you can use [DebugProbes.dumpCoroutines] to print all active (suspended or running) coroutines, including their state, creation and 12suspension stacktraces. 13Additionally, it is possible to process the list of such coroutines via [DebugProbes.dumpCoroutinesInfo] or dump isolated parts 14of coroutines hierarchy referenced by a [Job] or [CoroutineScope] instances using [DebugProbes.printJob] and [DebugProbes.printScope] respectively. 15 16This module also provides an automatic [BlockHound](https://github.com/reactor/BlockHound) integration 17that detects when a blocking operation was called in a coroutine context that prohibits it. In order to use it, 18please follow the BlockHound [quick start guide]( 19https://github.com/reactor/BlockHound/blob/1.0.2.RELEASE/docs/quick_start.md). 20 21### Using in your project 22 23Add `kotlinx-coroutines-debug` to your project test dependencies: 24``` 25dependencies { 26 testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-debug:1.4.0' 27} 28``` 29 30### Using in unit tests 31 32For JUnit4 debug module provides special test rule, [CoroutinesTimeout], for installing debug probes 33and to dump coroutines on timeout to simplify tests debugging. 34 35Its usage is better demonstrated by the example (runnable code is [here](test/TestRuleExample.kt)): 36 37```kotlin 38class TestRuleExample { 39 @get:Rule 40 public val timeout = CoroutinesTimeout.seconds(1) 41 42 private suspend fun someFunctionDeepInTheStack() { 43 withContext(Dispatchers.IO) { 44 delay(Long.MAX_VALUE) // Hang method 45 } 46 } 47 48 @Test 49 fun hangingTest() = runBlocking { 50 val job = launch { 51 someFunctionDeepInTheStack() 52 } 53 job.join() // Join will hang 54 } 55} 56``` 57 58After 1 second, test will fail with `TestTimeoutException` and all coroutines (`runBlocking` and `launch`) and their 59stacktraces will be dumped to the console. 60 61### Using as JVM agent 62 63Debug module can also be used as a standalone JVM agent to enable debug probes on the application startup. 64You can run your application with an additional argument: `-javaagent:kotlinx-coroutines-debug-1.6.4.jar`. 65Additionally, on Linux and Mac OS X you can use `kill -5 $pid` command in order to force your application to print all alive coroutines. 66When used as Java agent, `"kotlinx.coroutines.debug.enable.creation.stack.trace"` system property can be used to control 67[DebugProbes.enableCreationStackTraces] along with agent startup. 68 69### Using in production environment 70 71It is possible to run an application in production environments with debug probes in order to monitor its 72state and improve its observability. 73For that, it is strongly recommended to switch off [DebugProbes.enableCreationStackTraces] property to significantly 74reduce the overhead of debug probes and make it insignificant. 75With creation stack-traces disabled, the typical overhead of enabled debug probes is a single-digit percentage of the total 76application throughput. 77 78 79### Example of usage 80 81Capabilities of this module can be demonstrated by the following example 82(runnable code is [here](test/Example.kt)): 83 84```kotlin 85suspend fun computeValue(): String = coroutineScope { 86 val one = async { computeOne() } 87 val two = async { computeTwo() } 88 combineResults(one, two) 89} 90 91suspend fun combineResults(one: Deferred<String>, two: Deferred<String>): String = 92 one.await() + two.await() 93 94suspend fun computeOne(): String { 95 delay(5000) 96 return "4" 97} 98 99suspend fun computeTwo(): String { 100 delay(5000) 101 return "2" 102} 103 104fun main() = runBlocking { 105 DebugProbes.install() 106 val deferred = async { computeValue() } 107 // Delay for some time 108 delay(1000) 109 // Dump running coroutines 110 DebugProbes.dumpCoroutines() 111 println("\nDumping only deferred") 112 DebugProbes.printJob(deferred) 113} 114``` 115 116Printed result will be: 117 118``` 119Coroutines dump 2018/11/12 21:44:02 120 121Coroutine "coroutine#2":DeferredCoroutine{Active}@289d1c02, state: SUSPENDED 122 at kotlinx.coroutines.DeferredCoroutine.await$suspendImpl(Builders.common.kt:99) 123 at ExampleKt.combineResults(Example.kt:11) 124 at ExampleKt$computeValue$2.invokeSuspend(Example.kt:7) 125 at ExampleKt$main$1$deferred$1.invokeSuspend(Example.kt:25) 126 (Coroutine creation stacktrace) 127 at kotlin.coroutines.intrinsics.IntrinsicsKt__IntrinsicsJvmKt.createCoroutineUnintercepted(IntrinsicsJvm.kt:116) 128 at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:25) 129 at kotlinx.coroutines.BuildersKt.async$default(Unknown Source) 130 at ExampleKt$main$1.invokeSuspend(Example.kt:25) 131 at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:32) 132 at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:233) 133 at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source) 134 at ExampleKt.main(Example.kt:23) 135 at ExampleKt.main(Example.kt) 136 137... More coroutines here ... 138 139Dumping only deferred 140"coroutine#2":DeferredCoroutine{Active}, continuation is SUSPENDED at line kotlinx.coroutines.DeferredCoroutine.await$suspendImpl(Builders.common.kt:99) 141 "coroutine#3":DeferredCoroutine{Active}, continuation is SUSPENDED at line ExampleKt.computeOne(Example.kt:14) 142 "coroutine#4":DeferredCoroutine{Active}, continuation is SUSPENDED at line ExampleKt.computeTwo(Example.kt:19) 143``` 144 145### Status of the API 146 147API is experimental, and it is not guaranteed it won't be changed (while it is marked as `@ExperimentalCoroutinesApi`). 148Like the rest of experimental API, `DebugProbes` is carefully designed, tested and ready to use in both test and production 149environments. It is marked as experimental to leave us the room to enrich the output data in a potentially backwards incompatible manner 150to further improve diagnostics and debugging experience. 151 152The output format of [DebugProbes] can be changed in the future and it is not recommended to rely on the string representation 153of the dump programmatically. 154 155### Debug agent and Android 156 157Android runtime does not support Instrument API necessary for `kotlinx-coroutines-debug` to function, triggering `java.lang.NoClassDefFoundError: Failed resolution of: Ljava/lang/management/ManagementFactory;`, 158and it is not possible to use coroutine debugger along with Android emulator. 159 160<!--- 161Make an exception googlable 162java.lang.NoClassDefFoundError: Failed resolution of: Ljava/lang/management/ManagementFactory; 163 at kotlinx.coroutines.repackaged.net.bytebuddy.agent.ByteBuddyAgent$ProcessProvider$ForCurrentVm$ForLegacyVm.resolve(ByteBuddyAgent.java:1055) 164 at kotlinx.coroutines.repackaged.net.bytebuddy.agent.ByteBuddyAgent$ProcessProvider$ForCurrentVm.resolve(ByteBuddyAgent.java:1038) 165 at kotlinx.coroutines.repackaged.net.bytebuddy.agent.ByteBuddyAgent.install(ByteBuddyAgent.java:374) 166 at kotlinx.coroutines.repackaged.net.bytebuddy.agent.ByteBuddyAgent.install(ByteBuddyAgent.java:342) 167 at kotlinx.coroutines.repackaged.net.bytebuddy.agent.ByteBuddyAgent.install(ByteBuddyAgent.java:328) 168 at kotlinx.coroutines.debug.internal.DebugProbesImpl.install(DebugProbesImpl.kt:39) 169 at kotlinx.coroutines.debug.DebugProbes.install(DebugProbes.kt:49) 170--> 171 172#### Build failures due to duplicate resource files 173 174Building an Android project that depends on `kotlinx-coroutines-debug` (usually introduced by being a transitive 175dependency of `kotlinx-coroutines-test`) may fail with `DuplicateRelativeFileException` for `META-INF/AL2.0`, 176`META-INF/LGPL2.1`, or `win32-x86/attach_hotspot_windows.dll` when trying to merge the Android resource. 177 178The problem is that Android merges the resources of all its dependencies into a single directory and complains about 179conflicts, but: 180* `kotlinx-coroutines-debug` transitively depends on JNA and JNA-platform, both of which include license files in their 181 META-INF directories. Trying to merge these files leads to conflicts, which means that any Android project that 182 depends on JNA and JNA-platform will experience build failures. 183* Additionally, `kotlinx-coroutines-debug` embeds `byte-buddy-agent` and `byte-buddy`, along with their resource files. 184 Then, if the project separately depends on `byte-buddy`, merging the resources of `kotlinx-coroutines-debug` with ones 185 from `byte-buddy` and `byte-buddy-agent` will lead to conflicts as the resource files are duplicated. 186 187One possible workaround for these issues is to add the following to the `android` block in your gradle file for the 188application subproject: 189```groovy 190 packagingOptions { 191 // for JNA and JNA-platform 192 exclude "META-INF/AL2.0" 193 exclude "META-INF/LGPL2.1" 194 // for byte-buddy 195 exclude "META-INF/licenses/ASM" 196 pickFirst "win32-x86-64/attach_hotspot_windows.dll" 197 pickFirst "win32-x86/attach_hotspot_windows.dll" 198 } 199``` 200This will cause the resource merge algorithm to exclude the problematic license files altogether and only leave a single 201copy of the files needed for `byte-buddy-agent` to work. 202 203Alternatively, avoid depending on `kotlinx-coroutines-debug`. In particular, if the only reason why this library a 204dependency of your project is that `kotlinx-coroutines-test` in turn depends on it, you may change your dependency on 205`kotlinx.coroutines.test` to exclude `kotlinx-coroutines-debug`. For example, you could replace 206```kotlin 207androidTestImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:$coroutines_version") 208``` 209with 210```groovy 211androidTestImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:$coroutines_version") { 212 exclude group: "org.jetbrains.kotlinx", module: "kotlinx-coroutines-debug" 213} 214``` 215<!--- 216Snippets of stacktraces for googling: 217 218org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':app:mergeDebugAndroidTestJavaResource'. 219 ... 220Caused by: org.gradle.workers.intelrnal.DefaultWorkerExecutor$WorkExecutionException: A failure occurred while executing com.android.build.gradle.internal.tasks.Workers$ActionFacade 221 ... 222Caused by: com.android.builder.merge.DuplicateRelativeFileException: More than one file was found with OS independent path 'META-INF/AL2.0'. 223 at com.android.builder.merge.StreamMergeAlgorithms.lambda$acceptOnlyOne$2(StreamMergeAlgorithms.java:85) 224 at com.android.builder.merge.StreamMergeAlgorithms.lambda$select$3(StreamMergeAlgorithms.java:106) 225 at com.android.builder.merge.IncrementalFileMergerOutputs$1.create(IncrementalFileMergerOutputs.java:88) 226 at com.android.builder.merge.DelegateIncrementalFileMergerOutput.create(DelegateIncrementalFileMergerOutput.java:64) 227 at com.android.build.gradle.internal.tasks.MergeJavaResourcesDelegate$run$output$1.create(MergeJavaResourcesDelegate.kt:230) 228 at com.android.builder.merge.IncrementalFileMerger.updateChangedFile(IncrementalFileMerger.java:242) 229 at com.android.builder.merge.IncrementalFileMerger.mergeChangedInputs(IncrementalFileMerger.java:203) 230 at com.android.builder.merge.IncrementalFileMerger.merge(IncrementalFileMerger.java:80) 231 at com.android.build.gradle.internal.tasks.MergeJavaResourcesDelegate.run(MergeJavaResourcesDelegate.kt:276) 232 at com.android.build.gradle.internal.tasks.MergeJavaResRunnable.run(MergeJavaResRunnable.kt:81) 233 at com.android.build.gradle.internal.tasks.Workers$ActionFacade.run(Workers.kt:242) 234 at org.gradle.workers.internal.AdapterWorkAction.execute(AdapterWorkAction.java:50) 235 at org.gradle.workers.internal.DefaultWorkerServer.execute(DefaultWorkerServer.java:50) 236 at org.gradle.workers.internal.NoIsolationWorkerFactory$1$1.create(NoIsolationWorkerFactory.java:63) 237 at org.gradle.workers.internal.NoIsolationWorkerFactory$1$1.create(NoIsolationWorkerFactory.java:59) 238 at org.gradle.internal.classloader.ClassLoaderUtils.executeInClassloader(ClassLoaderUtils.java:98) 239 at org.gradle.workers.internal.NoIsolationWorkerFactory$1.lambda$execute$0(NoIsolationWorkerFactory.java:59) 240 at org.gradle.workers.internal.AbstractWorker$1.call(AbstractWorker.java:44) 241 at org.gradle.workers.internal.AbstractWorker$1.call(AbstractWorker.java:41) 242 at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:416) 243 at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:406) 244 at org.gradle.internal.operations.DefaultBuildOperationExecutor$1.execute(DefaultBuildOperationExecutor.java:165) 245 at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:250) 246 at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:158) 247 at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:102) 248 at org.gradle.internal.operations.DelegatingBuildOperationExecutor.call(DelegatingBuildOperationExecutor.java:36) 249 at org.gradle.workers.internal.AbstractWorker.executeWrappedInBuildOperation(AbstractWorker.java:41) 250 at org.gradle.workers.internal.NoIsolationWorkerFactory$1.execute(NoIsolationWorkerFactory.java:53) 251 at org.gradle.workers.internal.DefaultWorkerExecutor.lambda$submitWork$2(DefaultWorkerExecutor.java:200) 252 at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.runExecution(DefaultConditionalExecutionQueue.java:215) 253 at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.runBatch(DefaultConditionalExecutionQueue.java:164) 254 at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.run(DefaultConditionalExecutionQueue.java:131) 255 256Execution failed for task ':app:mergeStagingDebugAndroidTestJavaResource'. 257Execution failed for task ':app:mergeDebugAndroidTestJavaResource'. 258Execution failed for task ':app:mergeDebugTestJavaResource' 259 260More than one file was found with OS independent path 'META-INF/LGPL2.1' 261More than one file was found with OS independent path 'win32-x86/attach_hotspot_windows.dll' 262More than one file was found with OS independent path 'win32-x86-64/attach_hotspot_windows.dll' 263--> 264<!--- MODULE kotlinx-coroutines-core --> 265<!--- INDEX kotlinx.coroutines --> 266 267[Job]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-job/index.html 268[CoroutineScope]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-coroutine-scope/index.html 269 270<!--- MODULE kotlinx-coroutines-debug --> 271<!--- INDEX kotlinx.coroutines.debug --> 272 273[DebugProbes]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug/-debug-probes/index.html 274[DebugProbes.install]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug/-debug-probes/install.html 275[DebugProbes.dumpCoroutines]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug/-debug-probes/dump-coroutines.html 276[DebugProbes.dumpCoroutinesInfo]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug/-debug-probes/dump-coroutines-info.html 277[DebugProbes.printJob]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug/-debug-probes/print-job.html 278[DebugProbes.printScope]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug/-debug-probes/print-scope.html 279[DebugProbes.enableCreationStackTraces]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug/-debug-probes/enable-creation-stack-traces.html 280 281<!--- INDEX kotlinx.coroutines.debug.junit4 --> 282 283[CoroutinesTimeout]: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-debug/kotlinx.coroutines.debug.junit4/-coroutines-timeout/index.html 284 285<!--- END --> 286