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.

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.

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.

Flow

This version is the first stable release of Flow API.

All Flow API not marked with @FlowPreview or @ExperimentalCoroutinesApi annotations are stable and here to stay.
Flow declarations marked with @ExperimentalCoroutinesApi have the same guarantees as regular experimental API.
Please note that API marked with @FlowPreview have weak guarantees on source, binary and semantic compatibility.

Changelog

• A new guide section about Flow.
• CoroutineDispatcher.asExecutor extension (#1450).
• Fixed bug when select statement could report the same exception twice (#1433).
• Fixed context preservation in flatMapMerge in a case when collected values were immediately emitted to another flow (#1440).
• Reactive Flow integrations enclosing files are renamed for better interoperability with Java.
• Default buffer size in all Flow operators is increased to 64.
• Kotlin updated to 1.3.50.

Flow improvements

• Operators for UI programming are reworked for the sake of consistency, naming scheme for operator overloads is introduced:

  • combineLatest is deprecated in the favor of combine.
  • combineTransform operator for non-trivial transformations (#1224).
  • Top-level combine and combineTransform overloads for multiple flows (#1262).
  • switchMap is deprecated. flatMapLatest, mapLatest and transformLatest are introduced instead (#1335).
  • collectLatest terminal operator (#1269).

• Improved cancellation support in flattenMerge (#1392).

• channelFlow cancellation does not leak to the parent (#1334).

• Fixed flow invariant enforcement for suspend fun main (#1421).

• delayEach and delayFlow are deprecated (#1429).

General changes

• Integration with Reactor context

  • Propagation of the coroutine context of await calls into Mono/Flux builder.
  • Publisher.asFlow propagates coroutine context from collect call to the Publisher.
  • New Flow.asFlux builder.

• ServiceLoader-code is adjusted to avoid I/O on the Main thread on newer (3.6.0+) Android toolchain.

• Stacktrace recovery support for minified builds on Android (#1416).

• Guava version in kotlinx-coroutines-guava updated to 28.0.

• setTimeout-based JS dispatcher for platforms where process is unavailable (#1404).

• Native, JS and common modules are added to kotlinx-coroutines-bom.

• Fixed bug with ignored acquiredPermits in Semaphore (#1423).

Flow

• Core Flow API is promoted to stable
• New basic Flow operators: withIndex, collectIndexed, distinctUntilChanged overload
• New core Flow operators: onStart and onCompletion
• ReceiveChannel.consumeAsFlow and emitAll (#1340)

General changes

• Kotlin updated to 1.3.41
• Added kotlinx-coroutines-bom with Maven Bill of Materials (#1110)
• Reactive integrations are seriously improved
  • All builders now are top-level functions instead of extensions on CoroutineScope and prohibit Job instance in their context to simplify lifecycle management
  • Fatal exceptions are handled consistently (#1297)
  • Integration with Reactor Context added (#284)
• Stacktrace recovery for suspend fun main (#1328)
• CoroutineScope.cancel extension with message (#1338)
• Protection against non-monotonic clocks in delay (#1312)
• Duration.ZERO is handled properly in JDK 8 extensions (#1349)
• Library code is adjusted to be more minification-friendly

• Kotlin updated to 1.3.40.
• Flow exception transparency concept.
• New declarative Flow operators: onCompletion, catch, retryWhen, launchIn. onError* operators are deprecated in favour of catch. (#1263)
• Publisher.asFlow is integrated with buffer operator.
• Publisher.openSubscription default request size is 1 instead of 0 (#1267).

• Kotlin updated to 1.3.40.

Flow:

• Core Flow interfaces and operators are graduated from preview status to experimental.
• Context preservation invariant rework (#1210).
  • channelFlow and callbackFlow replacements for flowViaChannel for concurrent flows or callback-based APIs.
  • flow prohibits emissions from non-scoped coroutines by default and recommends to use channelFlow instead to avoid most of the concurrency-related bugs.
• Flow cannot be implemented directly
  • AbstractFlow is introduced for extension (e.g. for managing state) and ensures all context preservation invariants.
• Buffer size is decoupled from all operators that imply channel usage (#1233)
  • buffer operator can be used to adjust buffer size of any buffer-dependent operator (e.g. channelFlow, flowOn and flatMapMerge).
  • conflate operator is introduced.
• Flow performance is significantly improved.
• New operators: scan, scanReduce, first, emitAll.
• flowWith and flowViaChannel are deprecated.
• retry ignores cancellation exceptions from upstream when the flow was externally cancelled (#1122).
• combineLatest overloads for multiple flows (#1193).
• Fixed numerical overflow in drop operator.

Channels:

• consumeEach is promoted to experimental API (#1080).
• Conflated channels always deliver the latest value after closing (#332, #1235).
• Non-suspending ChannelIterator.next to improve iteration performance (#1162).
• Channel exception types are consistent with produce and are no longer swallowed as cancellation exceptions in case of programmatic errors (#957, #1128).
• All operators on channels (that were prone to coroutine leaks) are deprecated in the favor of Flow.

General changes:

• Kotlin updated to 1.3.31
• Semaphore implementation (#1088)
• Loading of Dispatchers.Main is tweaked so the latest version of R8 can completely remove I/O when loading it (#1231).
• Performace of all JS dispatchers is significantly improved (#820).
• withContext checks cancellation status on exit to make reasoning about sequential concurrent code easier (#1177).
• Consistent exception handling mechanism for complex hierarchies (#689).
• Convenient overload for CoroutinesTimeout.seconds (#1184).
• Fix cancellation bug in onJoin (#1130).
• Prevent internal names clash that caused errors for ProGuard (#1159).
• POSIX's nanosleep as delay in runBlocking in K/N (#1225).

Major:

• Infrastructure for testing coroutine-specific code in kotlinx-coroutines-test: runBlockingTest, TestCoroutineScope and TestCoroutineDispatcher, contributed by Sean McQuillan (@objcode).
• Job.asCompletableFuture extension in jdk8 module (#1113).

Flow improvements:

• flowViaChannel rework: block parameter is no longer suspending, but provides CoroutineScope receiver and allows conflated channel (#1081, #1112).
• New operators: switchMap, sample, debounce (#1107).
• consumerEach is deprecated for removal on Publisher, ObservableSource and MaybeSource, collect extension is introduced instead (#1080).

Other:

• Race in Job.join and concurrent cancellation is fixed (#1123).
• Stacktrace recovery machinery improved.
• Atomicfu-related bug fixes: publish transformed sources, do not propagate transitive atomicfu dependency (#1064, #1116).
• Misplaced resources are removed from the final jar (#1131).