Package detail

kotlinx-coroutines-core

Kotlin840Apache-2.01.7.3

Library support for Kotlin coroutines

Kotlin, async, coroutines, JavaScript, JetBrains

readme

kotlinx.coroutines

Library support for Kotlin coroutines in Kotlin/JS.

suspend fun main() = coroutineScope {
    launch { 
       delay(1000)
       println("Kotlin Coroutines World!") 
    }
    println("Hello")
}

Documentation

Guide to kotlinx.coroutines by example on JVM (read it first)
Full kotlinx.coroutines API reference

changelog

Change log for kotlinx.coroutines

Version 1.10.2

Fixed the kotlinx-coroutines-debug JAR file including the module-info.class file twice, resulting in failures in various tooling (#4314). Thanks, @RyuNen344!
Fixed Flow.stateIn hanging when the scope is cancelled in advance or the flow is empty (#4322). Thanks, @francescotescari!
Improved handling of dispatcher failures in .limitedParallelism (#4330) and during flow collection (#4272).
Fixed runBlocking failing to run its coroutine to completion in some cases if its JVM thread got interrupted (#4399).
Small tweaks, fixes, and documentation improvements.

Version 1.10.1

Fixed binary incompatibility introduced for non-JVM targets in #4261 (#4309).

Version 1.10.0

Kotlin was updated to 2.1.0 (#4284).
Introduced Flow.any, Flow.all, and Flow.none (#4212). Thanks, @CLOVIS-AI!
Reorganized kotlinx-coroutines-debug and kotlinx-coroutines-core code to avoid a split package between the two artifacts (#4247). Note that directly referencing kotlinx.coroutines.debug.AgentPremain must now be replaced with kotlinx.coroutines.debug.internal.AgentPremain. Thanks, @sellmair!
No longer shade byte-buddy in kotlinx-coroutines-debug, reducing the artifact size and simplifying the build configuration of client code. Thanks, @sellmair!
Fixed NullPointerException when using Java-deserialized kotlinx-coroutines-core exceptions (#4291). Thanks, @AlexRiedler!
Properly report exceptions thrown by CoroutineDispatcher.dispatch instead of raising internal errors (#4091). Thanks, @zuevmaxim!
Fixed a bug that delayed scheduling of a Dispatchers.Default or Dispatchers.IO task after a yield() in rare scenarios (#4248).
Fixed a bug that prevented the main() coroutine on Wasm/WASI from executing after a delay() call in some scenarios (#4239).
Fixed scheduling of runBlocking tasks on Kotlin/Native that arrive after the runBlocking block was exited (#4245).
Fixed some terminal Flow operators sometimes resuming without taking cancellation into account (#4254). Thanks, @jxdabc!
Fixed a bug on the JVM that caused coroutine-bound ThreadLocal values not to get cleaned when using non-CoroutineDispatcher continuation interceptors (#4296).
Small tweaks, fixes, and documentation improvements.

Version 1.9.0

Features

Wasm/WASI target support (#4064). Thanks, @igoriakovlev!
limitedParallelism now optionally accepts the name of the dispatcher view for easier debugging (#4023).
No longer initialize Dispatchers.IO on the JVM when other standard dispatchers are accessed (#4166). Thanks, @metalhead8816!
Introduced the Flow<T>.chunked(size: Int): Flow<List<T>> operator that groups emitted values into groups of the given size (#1290).
Closeable dispatchers are instances of AutoCloseable now (#4123).

Fixes

Calling hasNext on a Channel's iterator is idempotent (#4065). Thanks, @gitpaxultek!
CoroutineScope() created without an explicit dispatcher uses Dispatchers.Default on Native (#4074). Thanks, @whyoleg!
Fixed a bug that prevented non-Android Dispatchers.Main from initializing when the Firebase dependency is used (#3914).
Ensured a more intuitive ordering of tasks in runBlocking (#4134).
Forbid casting a Mutex to Semaphore (#4176).
Worked around a stack overflow that may occur when calling asDeferred on a Future many times (#4156).

Deprecations and promotions

Advanced the deprecation levels for BroadcastChannel-based API (#4197).
Advanced the deprecation levels for the old kotlinx-coroutines-test API (#4198).
Deprecated Job.cancelFutureOnCompletion (#4173).
Promoted CoroutineDispatcher.limitedParallelism to stable (#3864).
Promoted CoroutineStart.ATOMIC from ExperimentalCoroutinesApi to DelicateCoroutinesApi (#4169).
Promoted CancellableContinuation.resume with an onCancellation lambda to stable, providing extra arguments to the lambda (#4088).
Marked the classes and interfaces that are not supposed to be inherited from with the new InternalForInheritanceCoroutinesApi opt-in (#3770).
Marked the classes and interfaces inheriting from which is not stable with the new ExperimentalForInheritanceCoroutinesApi opt-in (#3770).

Other

Kotlin was updated to 2.0 (#4137).
Reworked the documentation for CoroutineStart and Channel-based API (#4147, #4148, #4167). Thanks, @globsterg!
Simplified the internal implementation of Job (#4053).
Small tweaks, fixes, and documentation improvements.

Version 1.9.0-RC.2

Advanced the deprecation levels for BroadcastChannel-based API (#4197).
Advanced the deprecation levels for the old kotlinx-coroutines-test API (#4198).
Promoted CoroutineStart.ATOMIC from ExperimentalCoroutinesApi to DelicateCoroutinesApi (#4169).
Reworked the documentation for CoroutineStart and Channel-based API (#4147, #4148, #4167). Thanks, @globsterg!
Forbid casting a Mutex to Semaphore (#4176).
Deprecated Job.cancelFutureOnCompletion (#4173).
Worked around a stack overflow that may occur when calling asDeferred on a Future many times (#4156).
Fixed a bug that disallowed setting a custom probeCoroutineResumed when starting coroutines with UNDISPATCHED (#4162).
No longer initialize Dispatchers.IO on the JVM when other standard dispatchers are accessed (#4166). Thanks, @metalhead8816!
Small tweaks, fixes, and documentation improvements.

Version 1.9.0-RC

Kotlin was updated to 2.0 (#4137).
Introduced the Flow<T>.chunked(size: Int): Flow<List<T>> operator that groups emitted values into groups of the given size (#1290).
Closeable dispatchers are instances of AutoCloseable now (#4123).
limitedParallelism now optionally accepts the name of the dispatcher view for easier debugging (#4023).
Marked the classes and interfaces that are not supposed to be inherited from with the new InternalForInheritanceCoroutinesApi opt-in (#3770).
Marked the classes and interfaces inheriting from which is not stable with the new ExperimentalForInheritanceCoroutinesApi opt-in (#3770).
Wasm/WASI target support (#4064). Thanks, @igoriakovlev!
Promoted CoroutineDispatcher.limitedParallelism to stable (#3864).
Promoted CancellableContinuation.resume with an onCancellation lambda to stable, providing extra arguments to the lambda (#4088).
Ensured a more intuitive ordering of tasks in runBlocking (#4134).
Simplified the internal implementation of Job (#4053).
Fixed a bug that prevented non-Android Dispatchers.Main from initializing when the Firebase dependency is used (#3914).
Calling hasNext on a Channel's iterator is idempotent (#4065). Thanks, @gitpaxultek!
CoroutineScope() created without an explicit dispatcher uses Dispatchers.Default on Native (#4074). Thanks, @whyoleg!
Small tweaks and documentation fixes.

Version 1.8.1

Remove the @ExperimentalTime annotation from usages of TimeSource (#4046). Thanks, @hfhbd!
Introduce a workaround for an Android bug that caused an occasional NullPointerException when setting the StateFlow value on old Android devices (#3820).
No longer use kotlin.random.Random as part of Dispatchers.Default and Dispatchers.IO initialization (#4051).
Flow.timeout throws the exception with which the channel was closed (#4071).
Small tweaks and documentation fixes.

Changelog relative to version 1.8.1-Beta

Flow.timeout throws the exception with which the channel was closed (#4071).
Small documentation fixes.

Version 1.8.1-Beta

Remove the @ExperimentalTime annotation from usages of TimeSource (#4046). Thanks, @hfhbd!
Attempt a workaround for an Android bug that caused an occasional NullPointerException when setting the StateFlow value on old Android devices (#3820).
No longer use kotlin.random.Random as part of Dispatchers.Default and Dispatchers.IO initialization (#4051).
Small tweaks.

Version 1.8.0

Implement the library for the Web Assembly (Wasm) for JavaScript (#3713). Thanks @igoriakovlev!
Major Kotlin version update: was 1.8.20, became 1.9.21.
On Android, ensure that Dispatchers.Main != Dispatchers.Main.immediate (#3545, #3963).
Fixed a bug that caused Flow operators that limit cancel the upstream flow to forget that they were already finished if there is another such operator upstream (#4035, #4038)
kotlinx-coroutines-debug is published with the correct Java 9 module info (#3944).
kotlinx-coroutines-debug no longer requires manually setting DebugProbes.enableCoroutineCreationStackTraces to false, it's the default (#3783).
kotlinx-coroutines-test: set the default timeout of runTest to 60 seconds, added the ability to configure it on the JVM with the kotlinx.coroutines.test.default_timeout=10s (#3800).
kotlinx-coroutines-test: fixed a bug that could lead to not all uncaught exceptions being reported after some tests failed (#3800).
delay(Duration) rounds nanoseconds up to whole milliseconds and not down (#3920). Thanks @kevincianfarini!
Dispatchers.Default and the default thread for background work are guaranteed to use the same context classloader as the object containing it them (#3832).
It is guaranteed that by the time SharedFlow.collect suspends for the first time, it's registered as a subscriber for that SharedFlow (#3885). Before, it was also true, but not documented.
Atomicfu version is updated to 0.23.1, and Kotlin/Native atomic transformations are enabled, reducing the footprint of coroutine-heavy code (#3954).
Added a workaround for miscompilation of withLock on JS (#3881). Thanks @CLOVIS-AI!
Small tweaks and documentation fixes.

Changelog relative to version 1.8.0-RC2

kotlinx-coroutines-debug no longer requires manually setting DebugProbes.enableCoroutineCreationStackTraces to false, it's the default (#3783).
Fixed a bug that caused Flow operators that limit cancel the upstream flow to forget that they were already finished if there is another such operator upstream (#4035, #4038)
Small documentation fixes.

Version 1.8.0-RC2

Fixed a bug introduced in 1.8.0-RC where Mutex.onLock would not unlock if a non-local return was performed (#3985).
Fixed a bug introduced in 1.8.0-RC where depending on kotlinx-coroutines in Native code failed with a compilation error Could not find "org.jetbrains.kotlinx:atomicfu-cinterop-interop" (#3968).
Small documentation fixes.

Version 1.8.0-RC

Implement the library for the Web Assembly (Wasm) for JavaScript (#3713). Thanks @igoriakovlev!
On Android, ensure that Dispatchers.Main != Dispatchers.Main.immediate (#3545, #3963).
kotlinx-coroutines-debug is published with the correct Java 9 module info (#3944).
Major Kotlin version update: was 1.8.20, became 1.9.21.
kotlinx-coroutines-test: set the default timeout of runTest to 60 seconds, added the ability to configure it on the JVM with the kotlinx.coroutines.test.default_timeout=10s (#3800).
kotlinx-coroutines-test: fixed a bug that could lead to not all uncaught exceptions being reported after some tests failed (#3800).
delay(Duration) rounds nanoseconds up to whole milliseconds and not down (#3920). Thanks @kevincianfarini!
Dispatchers.Default and the default thread for background work are guaranteed to use the same context classloader as the object containing it them (#3832).
It is guaranteed that by the time SharedFlow.collect suspends for the first time, it's registered as a subscriber for that SharedFlow (#3885). Before, it was also true, but not documented.
Atomicfu version is updated to 0.23.1, and Kotlin/Native atomic transformations are enabled, reducing the footprint of coroutine-heavy code (#3954).
Added a workaround for miscompilation of withLock on JS (#3881). Thanks @CLOVIS-AI!
Small tweaks and documentation fixes.

Version 1.7.3

Disabled the publication of the multiplatform library metadata for the old (1.6 and earlier) KMP Gradle plugin (#3809).
Fixed a bug introduced in 1.7.2 that disabled the coroutine debugger in IDEA (#3822).

Version 1.7.2

Bug fixes and improvements

Coroutines debugger no longer keeps track of coroutines with empty coroutine context (#3782).
CopyableThreadContextElement now properly copies an element when crossing the coroutine boundary in flowOn (#3787). Thanks @wanyingd1996!
Coroutine timeouts no longer prevent K/N newSingleThreadContext from closing (#3768).
A non-linearizability in Mutex during tryLock/unlock sequence with owners is fixed (#3745).
Atomicfu version is updated to 0.21.0.

Version 1.7.1

Bug fixes and improvements

Special characters in coroutine names in JSON dumps are supported (#3747)
The binary compatibility of the experimental overload of runTest is restored (#3673)
Channels that don't use onUndeliveredElement now allocate less memory (#3646)

Version 1.7.0

Core API significant improvements

New Channel implementation with significant performance improvements across the API (#3621).
New select operator implementation: faster, more lightweight, and more robust (#3020).
Mutex and Semaphore now share the same underlying data structure (#3020).
Dispatchers.IO is added to K/N (#3205)
- newFixedThreadPool and Dispatchers.Default implementations on K/N were wholly rewritten to support graceful growth under load (#3595).
kotlinx-coroutines-test rework:
- Add the timeout parameter to runTest for the whole-test timeout, 10 seconds by default (#3270). This replaces the configuration of quiescence timeouts, which is now deprecated (#3603).
- The withTimeout exception messages indicate if the timeout used the virtual time (#3588).
- TestCoroutineScheduler, runTest, and TestScope API are promoted to stable (#3622).
- runTest now also fails if there were uncaught exceptions in coroutines not inherited from the test coroutine (#1205).

Breaking changes

Old K/N memory model is no longer supported (#3375).
New generic upper bounds were added to reactive integration API where the language since 1.8.0 dictates (#3393).
kotlinx-coroutines-core and kotlinx-coroutines-jdk8 artifacts were merged into a single artifact (#3268).
Artificial stackframes in stacktrace recovery no longer contain the \b symbol and are now navigable in IDE and supplied with proper documentation (#2291).
CoroutineContext.isActive returns true for contexts without any job in them (#3300).

Bug fixes and improvements

Kotlin version is updated to 1.8.20
Atomicfu version is updated to 0.20.2.
JavaFx version is updated to 17.0.2 in kotlinx-coroutines-javafx (#3671)..
JPMS is supported (#2237). Thanks @lion7!
BroadcastChannel and all the corresponding API are deprecated (#2680).
Added all supported K/N targets (#3601, #812, #855).
K/N Dispatchers.Default is backed by the number of threads equal to the number of available cores (#3366).
Fixed an issue where some coroutines' internal exceptions were not properly serializable (#3328).
Introduced Job.parent API (#3201).
Fixed a bug when TestScheduler leaked cancelled jobs (#3398).
TestScope.timeSource now provides comparable time marks (#3617). Thanks @hfhbd!
Fixed an issue when cancelled withTimeout handles were preserved in JS runtime (#3440).
Ensure awaitFrame only awaits a single frame when used from the main looper (#3432). Thanks @pablobaxter!
Obsolete Class-Path attribute was removed from kotlinx-coroutines-debug.jar manifest (#3361).
Fixed a bug when updateThreadContext operated on the parent context (#3411).
Added new Flow.filterIsInstance extension (#3240).
Dispatchers.Default thread name prefixes are now configurable with system property (#3231).
Added Flow.timeout operator as @FlowPreview (#2624). Thanks @pablobaxter!
Improved the performance of the future builder in case of exceptions (#3475). Thanks @He-Pin!
Mono.awaitSingleOrNull now waits for the onComplete signal (#3487).
Channel.isClosedForSend and Channel.isClosedForReceive are promoted from experimental to delicate (#3448).
Fixed a data race in native EventLoop (#3547).
Dispatchers.IO.limitedParallelism(valueLargerThanIOSize) no longer creates an additional wrapper (#3442). Thanks @dovchinnikov!
Various @FlowPreview and @ExperimentalCoroutinesApi are promoted to experimental and stable respectively (#3542, #3097, #3548).
Performance improvements in Dispatchers.Default and Dispatchers.IO (#3416, #3418).
Fixed a bug when internal suspendCancellableCoroutineReusable might have hanged (#3613).
Introduced internal API to process events in the current system dispatcher (#3439).
Global CoroutineExceptionHandler is no longer invoked in case of unprocessed future failure (#3452).
Performance improvements and reduced thread-local pressure for the withContext operator (#3592).
Improved performance of DebugProbes (#3527).
Fixed a bug when the coroutine debugger might have detected the state of a coroutine incorrectly (#3193).
CoroutineDispatcher.asExecutor() runs tasks without dispatching if the dispatcher is unconfined (#3683). Thanks @odedniv!
SharedFlow.toMutableList and SharedFlow.toSet lints are introduced (#3706).
Channel.invokeOnClose is promoted to stable API (#3358).
Improved lock contention in Dispatchers.Default and Dispatchers.IO during the startup phase (#3652).
Fixed a bug that led to threads oversubscription in Dispatchers.Default (#3642).
Fixed a bug that allowed limitedParallelism to perform dispatches even after the underlying dispatcher was closed (#3672).
Fixed a bug that prevented stacktrace recovery when the exception's constructor from cause was selected (#3714).
Improved sanitizing of stracktrace-recovered traces (#3714).
Introduced an internal flag to disable uncaught exceptions reporting in tests as a temporary migration mechanism (#3736).
Various documentation improvements and fixes.