v3.4.0-RC1

Reactor-Core 3.4.0.-RC1 is part of 2020.0.0-RC1 Release Train (codename Europium).

This first Release Candidate brings further changes to the Sinks API introduced in M2

This release note focuses on RC1-specific changes, but RC1 also contains all the changes released in 3.2.20.RELEASE and 3.3.10.RELEASE.

⚠️ Update considerations and deprecations

Processors and sinks update considerations

The most impactful change is the switch in focus from an API that emulates Subscriber (with void return types) to a lower level API that can consistently provide immediate feedback to a signalling attempt via the returned Emission. Now the later is prefixed with tryEmit. An emit API is offered as an initial problematic attempt at a higher level abstraction, but it had to be @Deprecated. See #2374 for potential ways to rewrite code that used to call onNext/next/emitNext-without-checking-returned-Emission in previous versions.

@simonbasle is also preparing a retrospective write up of all the changes through which the sinks API went in #2382.

emitXxx replaced with tryEmitXxx

• See #2319 : Split emitXxx/tryEmitXxx, more consistent use of hooks.

new Emission.FAIL_xxx error codes

• Emission.FAIL_NON_SERIALIZED (see #2342 Failing fast on non-serialized access to Sink)
• Emission.FAIL_ZERO_SUBSCRIBER (see #2338 Add new Emission FAIL_ZERO_SUBSCRIBER error code)

"safe" onBackpressureError() not exposed anymore

• See #2375 : Remove Sinks.many().multicast().onBackpressureError().

emitXxx part of the API to be removed / heavily reworked

• See #2374 : Deprecate Sinks emit{Next,Error,Complete} methods.

🐞 Bug fixes

• These are incremental improvements over the tryEmitNext API (previously emitNext in M2):
  • Handle ASYNC fusion in EmitterProcessor#onNext rather than emitNext (#2316)
  • #2330 Ensure we never throw from tryEmitNext (#2336)
  • #2342 Failing fast on non-serialized access to Sink (#2365)

✨ New features and improvements

• #2312 Add user provided state to Retry
• #2325 Add method to snapshot factory+global schedulers, used by VTS (#2326)
• #2328 Make ParallelFlux.subscribe(array) public to allow delegation
• Sinks related improvements over M2:
  • #2329 Improve Emission API: polish status helpers, add orThrow()
  • #2338 Add new Emission FAIL_ZERO_SUBSCRIBER error code
  • Add onBackpressureError() variant of the unicast Sink (#2347, #2367)
• [Polish] Add inners[] param to Operators dropMulticast private methods

📖 Documentation, Tests and Build

• [doc] As the custom javadoc tags are not displayed in all IDEs, turned discard/errorMode javadoc tags into plain paragraphs (#2136)
• [build] #2353 Use api for reactive streams api dependency import
• several typos and inconsistencies fixed by various contributors
• [doc] #2317 Add examples to deprecation notes of processors
• [test] Avoid potential infinite busy looping in tests
• [doc] Polish javadoc of the multicast onBackpressureBuffer Sinks (#2373)
• [doc] Polish variable names in snippet (#2351)

👍 Thanks to the following contributors that also participated to this release

@hamidshahid, @steppedreckoner

v3.3.10.RELEASE

Reactor-Core 3.3.10.RELEASE is part of Dysprosium-SR12 Release Train.

This maintenance release contains one small enhancement to DirectProcessor/EmitterProcessor.

This version also contains all changes from v3.2.20.RELEASE.

🪲 Bug fixes

• #2356 Have Direct/EmitterProcessor implement currentContext()

📖 Documentation, Tests and Build

• [build] #2308 align reactor-tools test output with others projects

v3.2.20.RELEASE

Reactor-Core 3.2.20.RELEASE is part of Californium-SR21 Release Train.

This is a maintenance release with a couple bugfixes, as well as build polish.

🪲 Bug fixes

• #2318 Prevent FlatMapInner to request if fused in SYNC mode
• #2362 Prevent ConcurrentModificationEx on bufferPredicate discard

📖 Documentation, Tests and Build

• [build] Various polish of Gradle build (deprecation warnings #2274, wrapper validation #2348)
• [test] #2343 migrate tests to JUnit 5
• [build] #2332 remove optional-dependency plugin from Gradle build
• [reactor-test] Allow add/addAll in AssertQueueSubscription test util (46324db)

👍 Thanks to the following contributors that also participated to this release

@seants, @sullis

v3.4.0-M2

Reactor-Core 3.4.0.-M2 is part of 2020.0.0-M2 Release Train (codename Europium).

This second milestone brings several important changes:

• further evolution of the way processors and sinks are obtained and used (following up on the changes initiated in M1)
• improvements of the Context related APIs
• improvements on the Flux and Mono metrics

This release note focuses on M2-specific changes, but M2 also contains all the changes released in 3.2.19.RELEASE, 3.3.8.RELEASE and 3.3.9.RELEASE.

⚠️ Update considerations and deprecations

Metrics update considerations

The name() operator is no longer used in metrics as a tag but as a prefix for the meter names (#1928):

This allows to use custom tags via the tag() operator, while ensuring unique enough meter names that all bear the same set of tags

The [name].flow.duration meter has a status tag that now differentiate between completed and completedEmpty (#2313)

This allows to detect eg. empty Monos, but code relying on the completed status should be updated to also take completedEmpty into account.

The [name].subscribed and [name].requested meters have had their unit dropped (#1807):

The unit is part of the name in some backends like prometheus, but the unit was redundant. So the requested amount and subscribers unit suffixes have been dropped (separator may vary depending on the metrics backend).

Processors and sinks update considerations

The FluxIdentityProcessor and Processors classes that were introduced in M1 have been rolled back, and Sinks reworked (#2218)

The ultimate goal is to remove the need for processors (or greatly diminish it) and adding processor-related APIs was deemed counterproductive...

The sinks from operators (FluxSinks and MonoSink in create) no longer have a common interface with the "standalone" sinks. The hierarchy has been simplified and we now have 4 uncorrelated interfaces: FluxSink and MonoSink (back to what they were in 3.3, oriented towards subscription-like usage) versus Sinks.One and Sinks.Many (both oriented towards publisher-like usage).

Sinks allow building the later two, with a tiered approach:

1. chose many() vs one() vs empty()
2. Then on many(), chose a flavor (unicast(), multicast(), replay())
3. Finally, fine tune the flavor to obtain a sink (eg. Sinks.many().multicast().onBackpressureError())

These can also be converted to processors efficiently, as their (private) implementation also implement FluxProcessor/MonoProcessor. NB: to convert from a Sinks.Many/Sinks.One to a processor where a processor is still relevant, use FluxProcessor.fromSink and MonoProcessor.fromSink.

The MonoProcessor class used to be concrete but final. It is now abstract (#1053, #2296)

Most of its implementation has been moved to package-private NextProcessor. This will allow to introduce more flavors of MonoProcessor, focusing that class on signaling a Processor<A, B> that is also a Mono<B>.

A new flavor VoidProcessor, has been also immediately added. It backs Sinks.empty() with less overhead than the old MonoProcessor.

Sinks.Many and Sinks.One APIs

Contrary to operator sinks, these two sinks are to be used more like publisher than like subscribers.

That is to say, they are expected to be passed down asFlux() or asMono(), so generally should accommodate multiple subscribers (except for Sinks.many().unicast()).

As a result they expose a different and more restrained API. Most relevant methods are the emitXxx methods, which are not fluent but return an Emission enum.
They can be seen as a "best effort" API, indicating failure through the enum rather than an exception (comparable to Queue#offer vs Queue#add in the JDK).

⚠️ Consequently, the Emission enum should be checked to detect error cases.

For instance, the EmitterProcessor used to sleep when its configured buffer was full and users continued trying to emit, effectively busy-looping until the internal queue would accept the pushed valued. This is effectively blocking, and can be problematic (#2049).

The equivalent sink, Sinks.many().multicast().onBackpressureBuffer(), doesn't sleep/block but immediately returns Emission.FAIL_OVERFLOW.

Note that to get the old behavior, one can manually loop on the emitNext attempt until it returns Emission.OK, sleeping for a few nanoseconds when it returns FAIL_OVERFLOW. But caller could also decide to fail after a number of retries rather than an infinite loop for instance...

Context APIs

ContextView introduction (#2279)

Knowing when a Context can be "written" vs when it cannot is complicated by the fact that operators that aim at exposing the contextual data only for reading still expose the full Context API, with write methods.

In M2, we introduce ContextView, a superinterface to Context that only bears the read methods of the context.

Operators that expose the context for the purpose of reading from it (and where trying to put or remove data would effectively be a no-op) now have an alternative exposing the ContextView, deprecating the old way:

• deferWithContext(Function<Context, P>) is superseded by deferContextual(Function<ContextView, P>)
• we introduce transformDeferredContextual(BiFunction<P1, ContextView, P2>)
• Signal#getContext() is superseded by Signal#getContextView()
• Mono.subscriberContext() is deprecated. No replacement is planned as deferContextual(Mono::just) is a readily available replacement.

A Context is already a ContextView. In case an API presents a ContextView but one really need a Context instead, use Context.of(ContextView).

Improve naming of context operators (#2148)

In 3.3, context operators are a bit confusing since they're only differentiated by their inputs. In 3.4 we deprecate these confusing names and provide alternatives:

• Mono.subscriberContext() is to be removed. Use Mono.deferContextual(Mono::just) instead, or even better try to rewrite the code to fully utilize the capacities of deferContextual and transformDeferredContextual operators (which could allow reading from the ContextView only once).
• subscriberContext(Context) is superseded by contextWrite(ContextView) (which better conveys that the entries in the input are added to the current Context)
• subscriberContext(Function<Context, Context>) is superseded by contextWrite(Function<Context, Context>)

Other update considerations

• Methods and classes deprecated in 3.3 have been removed (#2277)
  • to help with the retryWhen migration from legacy throwable-based function, a second adapter has been added (in both M2 and 3.3 latest release): Retry.withThrowable(Function<Flux<Throwable>, Publisher<?>>)
• subscribe(..., Consumer<Subscription>) variant has been deprecated (#1825):
  • too often, people misuse it to capture or log the Subscription but forget to request it, resulting in hangs
• Mono.subscribe(valueHandler, errorHandler) now passed errors in the valueHandler to the errorHandler (#1995)
• All instances of Scheduler are now expected to require start() call before usage (#1789)
  • the impact is limited as Schedulers.Factory-produced instances are started automatically by Schedulers factory methods (eg. Schedulers.parallel() or even Schedulers.newBoundedElastic())
• when encountering onError signal AFTER onComplete/onError, operators will now default to only logging the extraneous Throwable (#1431)
  • Same with a sequence that is subscribe without a error handler (#2176).
  • This can be tuned by setting a Hooks.onErrorDropped. The old behavior of throwing would cause issues and used to break the rules of Reactive Streams
• All operators that take a Duration now do their best to deal with it in nanosecond precision (#1734)
  • However this means that the maximum interpretable Duration is now Duration.ofNanos(Long.MAX_VALUE) (down from ofMillis(Long.MAX_VALUE). This leaves us with 296 years as the maximum duration, which should be enough for all intents and purposes...
• Schedulers.newElastic and Schedulers.elastic() are now deprecated, to be removed in 3.5

✨ New features and improvements

• fix #2253 redesign how MetricsRegistry is configured: one can now centrally chose the registry to use instead of micrometer's globalRegistry
• fix #2058 identify operators with scheduler through new scannable property (#2123)
• Allow "0" prefetch value in concatMap (#2202)
• fix #2220 Log context access in FINE(ST) level and with correct prefix
• Lazily instantiate exception in Mono#repeatWhenEmpty (#2221)

📖 Documentation, Tests and Build

• various cleanups in code, documentation, tests and build
• [doc] Document Android 21 desugaring options (#2232)

👍 Thanks to the following contributors that also participated to this release

@cnabro, @OlegDokuka, @seants, @yschimke, @robotmrv

v3.3.9.RELEASE

{TODO}

v3.3.8.RELEASE

Reactor-Core 3.3.8.RELEASE is part of Dysprosium-SR10 Release Train.

This maintenance release is a recommended update for all Reactor 3 users.

This version also contains all changes from v3.2.19.RELEASE.

🪲 Bug fixes

• Handle null publisher in MonoDelayUntil (#2245)
• fix #2260 Avoid onSubscribe race in FluxTimeout (#2266)

📖 Documentation, Tests and Build

• [doc] Fix Scheduler Javadoc (#2190)
• [doc] fix #2199 Fix typo in reference guide
• [build] fix #2264 add blockhound to testset
• [doc] Fix small error in TupleUtils asciidoc (#2201)
• [polish] fix #2246 Remove usage of globalRegistry in metrics tests
• [polish] FluxUsingWhenTest awaitility + order of capturing subscription
• [doc] fix #2257 Improve flatMapIterable prefetch javadoc

👍 Thanks to the following contributors that also participated to this release

@dennyac, @nicolasgavalda

v3.2.19.RELEASE

Reactor-Core 3.2.19.RELEASE is part of Californium-SR20 Release Train.

This is a maintenance release with a couple bugfixes, as well as build polish.

🪲 Bug fixes

• fix #2196: don't hang on repeatWhenEmpty + discard handler
• fix #2186 Align MonoCollect and MonoCollectList to avoid race condition leading to NullPointerException

📖 Documentation, Tests and Build

• [polish] In README Gradle snippet, put maven central repo first (#2248)
• [doc] fix #2212 Improve bufferTimeout() marble
• [build] fix #2251 refactor how micrometer integration is tested
• [build] Rework linking between check, japicmp and downloadBaseline tasks (#2226)
• [build] Bump Kotlin to 1.3.72 (#2247)
• [build] Polish travis CI build to use external script for JDK downloads (#2255)
• [build] fix #2241 Get rid of overcomplicated travis-build.sh but show progress
• [build] fix #2262 Make the fact that optional are not in pom anymore explicit
• [build] Fix input package rule for OSGi metadata generator (#2185)

👍 Thanks to the following contributors that also participated to this release

@arturdryomov, @gurkerl83, @rstoyanchev

v3.3.7.RELEASE

reactor-core 3.3.7.RELEASE is part of Dysprosium-SR9 Release Train.

✨ New features and improvements

🪲 Bug fixes

• Align MonoCollect and MonoCollectList to avoid race condition which leads to NullPointerException (#2186)
• Handle nulls from collectors in Flux.collect() (#2181)

📖 Documentation, Tests and Build

• [test] Improve thread regrowth test of boundedElastic/Elastic by considering negative values that might be produced as 0 (no regrowth, aka no increase in the number of active threads from the scheduler).
• [build] Ensure tools fat jar is the one published (#2189)
• [build] Fix input package rule for OSGi metadata generator (#2185)

👍 Thanks to the following contributors that also participated to this release

@rstoyanchev , @melix , @gurkerl83

v3.4.0-M1

Reactor-Core 3.4.0-M1 is the first MILESTONE in the 2020.0.0-M1 Release Train (codename Europium).

Note that in terms of content this milestone is also aligned with what was released in 3.3.7.RELEASE

⚠️ Update considerations and deprecations

• Introduce Sinks and deprecate concrete processors (#2188)
  • more detailed migration notes to come
• Deprecate Schedulers.elastic for 3.5 removal (#1893)
  • This further enforces the use of the boundedElastic flavor
• Remove schedulers deprecated in 3.3 (#2208)

✨ New features and improvements

• Handle nulls from collectors in Flux.collect() (#2181)
• Have push(emitter) delegate to push(emitter, backpressure) (#2177)
• Align implementations of MonoCollect to be comparable to MonoCollectList (#2186)
• Bump the perf baseline to 3.3.6

🪲 Bug fixes

• Fix input package rule for OSGi metadata generator (#2185)

📖 Documentation, Tests and Build

• [build] master is 3.4 Europium, introduce new versioning scheme (#2140)
• [build] Ensure tools fat jar is the one published (#2189)
• [doc] Make ParallelFlux runOn methods doc consistent about work stealing (#2170)
• [doc] Fix 'decided' typo in coreFeatures.adoc (#2174)

👍 Thanks to the following contributors that also participated to this release

@jonenst , @rstoyanchev , @Inego , @gurkerl83

v3.3.6.RELEASE

Reactor-Core 3.3.6.RELEASE is part of Dysprosium-SR8 Release Train.

✨ New features and improvements

• EnsureDeferredSubscription makes requests serially if there is racing between set / requestN (according to RS spec Rule 2.7)(#2164)
• Ensure FluxSwitchOnFirst serializes requests (according to RS spec Rule 2.7) (#2161)
• Ensures next element is dropped if UnicastProcessor disposed to avoid racing between onNext and dispose (#2180)
• Use ZoneId.of(String) to avoid blocking disk load during first access of Schedulers.boundedElastic() (#2143)

🪲 Bug fixes

• Accommodate ASYNC fusion in Mono.metrics() to avoid NullPointerException or hanging in certain cases (#2160 )
• Fix volatile read of first element and ConditionalSubscriber classcast in FluxSwitchOnFirst (#2166)
• Change the Subscription set by reportThrowInSubscribe to an instance compatible with QueueSubscription, preventing fused cases where a ClassCastException would be thrown. (#2152 )

📖 Documentation, Tests and Build

• [test] Fix publishOn scan test, hiccup before asserting BUFFERED
• [doc] Better describe Mono.first() and Mono.or() behavior (#2159)
• [doc] Fix typo Retry.fromFunction() instead of from() (#2172)
• [doc] Fix RetrySpec doc: throwablePredicate is actually filter (#2162)
• [doc] Document onCancel / onDipose limited to 1 use (#2015)
• [doc] Remove wrong curly braces in generate code example (#2110)
• [build] Have blockHoundTest fork JVM on every case (see #2144)
• [build] Consistently use tabs for gradle file indentation (#2157)
• [publication] Publish Gradle metadata, without optional dependencies (#2151)

👍 Thanks to the following contributors that also participated to this release

@alex-dukhno , @chakas , @berry120 , @OlegDokuka , @PyvesB , @josemalonsom