reactor/reactor-core

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Non-Blocking Reactive Foundation for the JVM

Stars: 5.2k
Forks: 1.3k
Open beginner issues: 0
Indexed issues: 75
Avg merge: 1d 21m
Merged PRs (30d): 15

Dominant language: Java
License: Apache-2.0
Last GitHub push: Sep 18, 2026
Latest indexed: Sep 19, 2026
Contributing guide: Contributing guide
Code of conduct: Code of conduct
Beginner labels: help wanted

Beginner friendly Everything

Open All

75 open issues indexed

refCount() never disconnects when a subscriber cancels during onSubscribe (regression in 3.8.0) Open

Difficulty 4/5 3-5 days Newbie friendliness 68/100

reactor/reactor-core#4387 · Opened Sep 8, 2026
mergeSequential and flatMapSequential do not discard elements buffered in inner queues Open

Difficulty 3/5 1-2 days Newbie friendliness 68/100

reactor/reactor-core#4379 · Opened Sep 3, 2026
Mono.sequenceEqual does not discard buffered elements on cancellation, error, or mismatch Open

Difficulty 3/5 1-2 days Newbie friendliness 55/100

reactor/reactor-core#4378 · Opened Sep 3, 2026
bufferTimeout with fairBackpressure emits a partial buffer when downstream demand resumes Open

Difficulty 2/5 1-3 hours Newbie friendliness 86/100

reactor/reactor-core#4377 · Opened Sep 3, 2026
Outdated FOSS used in reactive-streams-jvm Open

type/enhancement

Difficulty 4/5 3-5 days Newbie friendliness 35/100

reactor/reactor-core#4368 · Opened Aug 27, 2026
Provide a way for library-internal maintenance tasks to opt out of onSchedule decoration Open

type/enhancement

Difficulty 4/5 3-5 days Newbie friendliness 48/100

reactor/reactor-core#4338 · Opened Jul 26, 2026
`MonoSingle` propagates empty completion after cancellation Open

Difficulty 2/5 1-3 hours Newbie friendliness 78/100

reactor/reactor-core#4330 · 1 comment · Opened Jul 20, 2026
bufferWhile does not discard buffer-triggering element despite what the docs says Open

Difficulty 3/5 1-2 days Newbie friendliness 74/100

reactor/reactor-core#4316 · Opened Jul 8, 2026
flatMap double-counts produced when onErrorContinue resumes a Callable error Open

type/bug

Difficulty 2/5 1-3 hours Newbie friendliness 82/100

reactor/reactor-core#4290 · Opened Jun 25, 2026
FluxRefCount: shared upstream connection not released when subscriber cancels before connection is established Open

type/bug

Difficulty 4/5 3-5 days Newbie friendliness 45/100

reactor/reactor-core#4289 · 1 comment · Opened Jun 25, 2026
JSpecify-annotated `BiConsumer` of `onErrorContinue` should allow null as its second argument Open

Difficulty 2/5 1-3 hours Newbie friendliness 78/100

reactor/reactor-core#4285 · Opened Jun 19, 2026
Hosted Javadoc package-list/package-list returns 404 at projectreactor.io/docs/core/release/api/, breaking downstream -link / Dokka builds Open

type/documentation

Difficulty 4/5 3-5 days Newbie friendliness 45/100

reactor/reactor-core#4278 · Opened Jun 17, 2026
Validate historySize in SinkManyReplayProcessor#create(int, boolean) Open

type/bug

Difficulty 4/5 3-5 days Newbie friendliness 55/100

reactor/reactor-core#4274 · Opened Jun 9, 2026
Validate bufferSize and prefetch in operators Open

type/bug

Difficulty 3/5 1-2 days Newbie friendliness 68/100

reactor/reactor-core#4273 · Opened Jun 9, 2026
Flux.onBackpressureBuffer should validate maxSize Open

type/bug

Difficulty 3/5 1-2 days Newbie friendliness 68/100

reactor/reactor-core#4272 · 1 comment · Opened Jun 9, 2026
Document reactor-core-micrometer policy on registered metrics Open

type/documentation

Difficulty 2/5 1-3 hours Newbie friendliness 68/100

reactor/reactor-core#4271 · 1 comment · Opened Jun 9, 2026
Document reactor-core-micrometer name and tag operator use Open

type/documentation

Difficulty 2/5 1-3 hours Newbie friendliness 68/100

reactor/reactor-core#4270 · Opened Jun 9, 2026
Operators.multiplyCap should handle 0 properly Open

type/bug

Difficulty 2/5 1-3 hours Newbie friendliness 68/100

reactor/reactor-core#4269 · Opened Jun 9, 2026
busy loop causing deadlock in failure handler Open

Difficulty 3/5 1-2 days Newbie friendliness 68/100

reactor/reactor-core#4247 · Opened Apr 28, 2026
FluxTakeUntilOther does not cancel infinite Main on async companion error Open

Difficulty 3/5 1-2 days Newbie friendliness 74/100

reactor/reactor-core#4230 · Opened Mar 31, 2026
windowTimeout(maxSize, duration, fairBackpressure=true) does not propagate backpressure when window closes by timeout Open

type/enhancement

Difficulty 4/5 3-5 days Newbie friendliness 45/100

reactor/reactor-core#4205 · Opened Feb 17, 2026
Integer overflow in `bufferTimeout` Open

:question:need-triage

Difficulty 3/5 1-2 days Newbie friendliness 55/100

reactor/reactor-core#4185 · Opened Jan 20, 2026
DelegateServiceScheduler (via Schedulers) silently terminates periodic tasks on exception (ENC pattern) Open

:question:need-triage

Difficulty 3/5 1-2 days Newbie friendliness 45/100

reactor/reactor-core#4176 · Opened Jan 7, 2026
Flux#sampleFirst(Duration) marble diagram does not match implementation semantics Open

type/documentation

Difficulty 2/5 1-3 hours Newbie friendliness 65/100

reactor/reactor-core#4173 · Opened Jan 5, 2026
Is there a Reactor operator that automatically merges signals under backpressure (mergeOnBackpressure)? Open

type/enhancement

Difficulty 5/5 Over a week Newbie friendliness 30/100

reactor/reactor-core#4162 · Opened Dec 9, 2025
Schedulers.Factory.newThreadPerTaskBoundedElastic(int, int, ThreadFactory) is not publicly accessible Open

type/enhancement

Difficulty 4/5 3-5 days Newbie friendliness 45/100

reactor/reactor-core#4153 · 1 reaction · Opened Dec 4, 2025
Recursive subscribe/loop during service shutdown Open

Difficulty 5/5 Over a week Newbie friendliness 15/100

reactor/reactor-core#4124 · 1 comment · 1 reaction · Opened Oct 27, 2025
Provide bespoke thread-per-task-bounded-elastic scheduler Open

type/enhancement

Difficulty 5/5 Over a week Newbie friendliness 35/100

reactor/reactor-core#4102 · Opened Sep 24, 2025
Broken link to KDoc API in the documentation Open

Difficulty 2/5 1-3 hours Newbie friendliness 55/100

reactor/reactor-core#4079 · Opened Aug 20, 2025
Calling Mono.transform with Hooks.enableContextLossTracking() raises additional cancel signals Open

Difficulty 3/5 1-2 days Newbie friendliness 50/100

reactor/reactor-core#4060 · Opened Jul 28, 2025
retryWhen(backoff()) causing high resource usage in unit test Open

Difficulty 4/5 3-5 days Newbie friendliness 45/100

reactor/reactor-core#4054 · Opened Jul 11, 2025
Inconsistency in marble illustration for Flux.scan Open

help wanted type/documentation

Difficulty 2/5 1-3 hours Newbie friendliness 68/100

reactor/reactor-core#4042 · 3 comments · Opened Jun 23, 2025
Inconsistent behavior with VirtualTimeScheduler + `concatMap` operator + external scheduler Open

Difficulty 4/5 3-5 days Newbie friendliness 42/100

reactor/reactor-core#4031 · Opened May 31, 2025
Add asynchronous version of Flux::scan Open

type/enhancement

Difficulty 5/5 Over a week Newbie friendliness 35/100

reactor/reactor-core#4026 · Opened May 8, 2025
Added overloaded expectNextMatch to match multiple elements Open

status/need-user-input type/enhancement

Difficulty 3/5 1-2 days Newbie friendliness 42/100

reactor/reactor-core#4024 · 3 comments · Opened Apr 27, 2025
[Doc] The "Search in all Project Reactor Docs" text button leads to a 400 error page. Open

type/documentation

Difficulty 2/5 1-3 hours Newbie friendliness 35/100

reactor/reactor-core#4011 · Opened Mar 12, 2025
Hidden TOC appears with long header titles Open

help wanted type/documentation

Difficulty 3/5 1-2 days Newbie friendliness 38/100

reactor/reactor-core#4007 · 5 comments · Opened Mar 7, 2025
Streams shared via Flux.publish() replay elements emitted while there are no attached subscribers Open

area/connectableFlux status/need-investigation

Difficulty 4/5 3-5 days Newbie friendliness 35/100

reactor/reactor-core#3963 · 1 comment · 2 reactions · Opened Jan 7, 2025
FluxPublishOn to detach itself after further requests Open

status/need-user-input

Difficulty 4/5 3-5 days Newbie friendliness 42/100

reactor/reactor-core#3954 · 1 comment · Opened Dec 19, 2024
Mistake Open

type/enhancement

Difficulty 5/5 Over a week Newbie friendliness 1/100

reactor/reactor-core#3929 · 1 comment · 26 reactions · Opened Nov 8, 2024
Pull Request Policy Open

type/enhancement

Difficulty 5/5 Over a week Newbie friendliness 15/100

reactor/reactor-core#3925 · 7 comments · 45 reactions · Opened Nov 8, 2024
FluxZip fails to deliver error from concurrently running sources Open

type/bug

Difficulty 4/5 3-5 days Newbie friendliness 42/100

reactor/reactor-core#3917 · 6 comments · Opened Nov 5, 2024
autoConnect(0) seems to be broken - late subscribers receive data Open

area/connectableFlux status/need-investigation

Difficulty 4/5 3-5 days Newbie friendliness 35/100

reactor/reactor-core#3805 · 1 comment · Opened May 2, 2024
Add bufferWeightedWithin operator. Open

status/need-decision type/enhancement

Difficulty 4/5 3-5 days Newbie friendliness 35/100

reactor/reactor-core#3774 · 2 reactions · Opened Mar 22, 2024
[Flaky test] FluxCreateTest.fluxCreateOnRequestMultipleThreadsSlowProducer Open

type/test/flaky

Difficulty 4/5 3-5 days Newbie friendliness 30/100

reactor/reactor-core#3765 · Opened Mar 19, 2024
[Flaky test] FluxBlackboxProcessorVerification Open

type/test/flaky

Difficulty 4/5 3-5 days Newbie friendliness 30/100

reactor/reactor-core#3742 · 6 comments · Opened Mar 7, 2024
Auto-cancelled Sink still accepts emissions Open

type/bug

Difficulty 3/5 1-2 days Newbie friendliness 48/100

reactor/reactor-core#3715 · 11 comments · 2 reactions · Opened Feb 6, 2024
FluxSampleTimeout Javadoc concerns Open

status/need-decision

Difficulty 4/5 3-5 days Newbie friendliness 25/100

reactor/reactor-core#3689 · 3 comments · Opened Jan 9, 2024
[Suggestion] Create an operator that merges multiple ordered flux's into a single flow with optional fields for flux's with gaps in there keys Open

help wanted status/need-design type/enhancement

Difficulty 5/5 Over a week Newbie friendliness 25/100

reactor/reactor-core#3645 · 6 comments · 1 reaction · Opened Nov 21, 2023
[Flaky test] JCStress test hangs randomly `reactor.core.publisher.FluxSwitchOnFirstStressTest.InboundErrorLeadingToErrorAndOutboundCancelStressTest` Open

type/test/flaky

Difficulty 4/5 3-5 days Newbie friendliness 35/100

reactor/reactor-core#3627 · Opened Nov 2, 2023

reactor/reactor-core

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