1.4.0-M1

Breaking changes

• The concept of atomic cancellation in channels is removed. All operations in channels
  and corresponding Flow operators are cancellable in non-atomic way (#1813).
• If CoroutineDispatcher throws RejectedExecutionException, cancel current Job and schedule its execution to Dispatchers.IO (#2003).
• CancellableContinuation.invokeOnCancellation is invoked if the continuation was cancelled while its resume has been dispatched (#1915).
• Flow.singleOrNull operator is aligned with standard library and does not longer throw IllegalStateException on multiple values (#2289).

New experimental features

• SharedFlow primitive for managing hot sources of events with support of various subscription mechanisms, replay logs and buffering (#2034).
• Flow.shareIn and Flow.stateIn operators to transform cold instances of flow to hot SharedFlow and StateFlow respectively (#2047).

Other

• Support leak-free closeable resources transfer via onUndeliveredElement in channels (#1936).
• Changed ABI in reactive integrations for Java interoperability (#2182).
• Fixed ProGuard rules for kotlinx-coroutines-core (#2046, #2266).
• Lint settings were added to Flow to avoid accidental capturing of outer CoroutineScope for cancellation check (#2038).

External contributions

• Allow nullable types in Flow.firstOrNull and Flow.singleOrNull by @ansman (#2229).
• Add Publisher.awaitSingleOrDefault|Null|Else extensions by @sdeleuze (#1993).
• awaitCancellation top-level function by @LouisCAD (#2213).
• Significant part of our Gradle build scripts were migrated to .kts by @turansky.

Thank you for your contributions and participation in the Kotlin community!

1.3.9

• Support of CoroutineContext in Flow.asPublisher and similar reactive builders (#2155).
• Kotlin updated to 1.4.0.
• Transition to new HMPP publication scheme for multiplatform usages:
  • Artifacts kotlinx-coroutines-core-common and kotlinx-coroutines-core-native are removed.
  • For multiplatform usages, it's enough to depend directly on kotlinx-coroutines-core in commonMain source-set.
  • The same artifact coordinates can be used to depend on a platform-specific artifact in platform-specific source-set.

1.3.8

New experimental features

• Added Flow.transformWhile operator (#2065).
• Replaced scanReduce with runningReduce to be consistent with the Kotlin standard library (#2139).

Bug fixes and improvements

• Improve user experience for the upcoming coroutines debugger (#2093, #2118, #2131).
• Debugger no longer retains strong references to the running coroutines (#2129).
• Fixed race in Flow.asPublisher (#2109).
• Fixed ensureActive to work in the empty context case to fix IllegalStateException when using flow from suspend fun main (#2044).
• Fixed a problem with AbortFlowException in the Flow.first operator to avoid erroneous NoSuchElementException (#2051).
• Fixed JVM dependency on Android annotations (#2075).
• Removed keep rules mentioning kotlinx.coroutines.android from core module (#2061 by @mkj-gram).
• Corrected some docs and examples (#2062, #2071, #2076, #2107, #2098, #2127, #2078, #2135).
• Improved the docs and guide on flow cancellation (#2043).
• Updated Gradle version to 6.3 (it only affects multiplatform artifacts in this release).

1.3.7

• Fixed problem that triggered Android Lint failure (#2004).
• New Flow.cancellable() operator for cooperative cancellation (#2026).
• Emissions from flow builder now check cancellation status and are properly cancellable (#2026).
• New currentCoroutineContext function to use unambiguously in the contexts with CoroutineScope in receiver position (#2026).
• EXACTLY_ONCE contract support in coroutine builders.
• Various documentation improvements.

1.3.6

Flow

• StateFlow, new primitive for state handling (#1973, #1816, #395). The StateFlow is designed to eventually replace ConflatedBroadcastChannel for state publication scenarios. Please, try it and share your feedback. Note, that Flow-based primitives to publish events will be added later. For events you should continue to either use BroadcastChannel(1), if you put events into the StateFlow, protect them from double-processing with flags.
• Flow.onEmpty operator is introduced (#1890).
• Behavioural change in Flow.onCompletion, it is aligned with invokeOnCompletion now and passes CancellationException to its cause parameter (#1693).
• A lot of Flow operators have left its experimental status and are promoted to stable API.

Other

• runInterruptible primitive to tie cancellation with thread interruption for blocking calls. Contributed by @jxdabc (#1947).
• Integration module with RxJava3 is introduced. Contributed by @ZacSweers (#1883)
• Integration with BlockHound in kotlinx-coroutines-debug module (#1821, #1060).
• Memory leak in ArrayBroadcastChannel is fixed (#1885).
• Behavioural change in suspendCancellableCoroutine, cancellation is established before invoking passed block argument (#1671).
• Debug agent internals are moved into kotlinx-coroutines-core for better integration with IDEA. It should not affect library users and all the redundant code should be properly eliminated with R8.
• ClassCastException with reusable continuations bug is fixed (#1966).
• More precise scheduler detection for Executor.asCoroutineDispatcher (#1992).
• Kotlin updated to 1.3.71.

1.3.5

Version 1.3.5

• firstOrNull operators. Contributed by @bradynpoulsen
• java.time adapters for Flow operators. Contributed by @fvasco
• kotlin.time.Duration support (#1402). Contributed by @fvasco
• Memory leak with a mix of reusable and non-reusable continuations is fixed (#1855)
• DebugProbes are ready for production installation: its performance is increased, the flag to disable creation stacktraces to reduce the footprint is introduced (#1379, #1372)
• Stacktrace recovery workaround for Android 6.0 and earlier bug (#1866).
• New integration module: kotlinx-coroutines-jdk9 with adapters for java.util.concurrent.Flow
• BroadcastChannel.close properly starts lazy coroutine (#1713).
• kotlinx-coroutines-bom is published without Gradle metadata.
• Make calls to service loader in reactor integrations optimizable by R8 (#1817)

1.3.4

Flow

• Detect missing awaitClose calls in callbackFlow to make it less error-prone when used with callbacks (#1762, #1770). This change makes callbackFlow different from channelFlow
• ReceiveChannel.asFlow extension is introduced (#1490)
• Enforce exception transparency invariant in flow builder (#1657)
• Proper Dispatcher support in Flow reactive integrations (#1765)
• Batch Subscription.request calls in Flow reactive integration (#766)
• ObservableValue.asFlow added to JavaFx integration module (#1695)
• ObservableSource.asFlow added to RxJava2 integration module (#1768)

Other changes

• kotlinx-coroutines-core is optimized for R8, making it much smaller for Android usages (75 KB for 1.3.4 release)
• Performance of Dispatchers.Default is improved (#1704, #1706)
• Kotlin is updated to 1.3.70
• CoroutineDispatcher and ExecutorCoroutineDispatcher experimental coroutine context keys are introduced (#1805)
• Performance of various Channel operations is improved (#1565)

1.3.3

Flow

• Flow.take performance is significantly improved (#1538).
• Flow.merge operator (#1491).
• Reactive Flow adapters are promoted to stable API (#1549).
• Reusable cancellable continuations were introduced that improved the performance of various flow operators and iteration over channels (#1534).
• Fixed interaction of multiple flows with take operator (#1610).
• Throw NoSuchElementException instead of UnsupportedOperationException for empty Flow in reduce operator (#1659).
• onCompletion now rethrows downstream exceptions on emit attempt (#1654).
• Allow non-emitting withContext from flow builder (#1616).

Debugging

• DebugProbes.dumpCoroutines is optimized to be able to print the 6-digit number of coroutines (#1535).
• Properly capture unstarted lazy coroutines in debugger (#1544).
• Capture coroutines launched from within a test constructor with CoroutinesTimeout test rule (#1542).
• Stacktraces of Job-related coroutine machinery are shortened and prettified (#1574).
• Stacktrace recovery unification that should provide a consistent experience recover of stacktrace (#1597).
• Stacktrace recovery for withTimeout is supported (#1625).
• Do not recover exception with a single String parameter constructor that is not a message (#1631).

Other features

• Dispatchers.Default and Dispatchers.IO rework: CPU consumption is significantly lower, predictable idle threads termination (#840, #1046, #1286).
• Avoid ServiceLoader for loading Dispatchers.Main (#1572, #1557, #878, #1606).
• Consistently handle undeliverable exceptions in RxJava and Reactor integrations (#252, #1614).
• yield support in immediate dispatchers (#1474).
• CompletableDeferred.completeWith(result: Result<T>) is introduced.
• Added support for tvOS and watchOS-based Native targets (#1596).

Bug fixes and improvements

• Kotlin version is updated to 1.3.61.
• CoroutineDispatcher.isDispatchNeeded is promoted to stable API (#1014).
• Livelock and stackoverflows in mutual select expressions are fixed (#1411, #504).
• Properly handle null values in ListenableFuture integration (#1510).
• Making ReceiveChannel.cancel linearizability-friendly.
• Linearizability of Channel.close in a complex contended cases (#1419).
• ArrayChannel.isBufferEmpty atomicity is fixed (#1526).
• Various documentation improvements.
• Reduced bytecode size of kotlinx-coroutines-core, reduced size of minified dex when using basic functionality of kotlinx-coroutines.

1.3.2

This is a maintenance release that does not include any new features or bug fixes.

• Reactive integrations for Flow are promoted to stable API.
• Obsolete reactive API is deprecated.
• Deprecation level for API deprecated in 1.3.0 is increased.
• Various documentation improvements.

1.3.1

This is a minor update with various fixes:

• Flow: Fix recursion in combineTransform<T1, T2, R> (#1466).
• Fixed race in the Semaphore (#1477).
• Repaired some of ListenableFuture.kt's cancellation corner cases (#1441).
• Consistently unwrap exception in slow path of CompletionStage.asDeferred (#1479).
• Various fixes in documentation (#1496, #1476, #1470, #1468).
• Various cleanups and additions in tests.

Note: Kotlin/Native artifacts are now published with Gradle metadata format version 1.0, so you will need Gradle version 5.3 or later to use this version of kotlinx.coroutines in your Kotlin/Native project.