clojure/core.async

core.async

A Clojure library providing facilities for async programming and communication.

Documentation

• Rationale
• API docs
• Code walkthrough

Presentations

• Rich Hickey on core.async
• Tim Baldridge on core.async from Clojure/conj 2013 (code).
• Tim Baldridge on go macro internals - part 1 part 2

Releases and Dependency Information

This project follows the version scheme MAJOR.MINOR.COMMITS where MAJOR and MINOR provide some relative indication of the size of the change, but do not follow semantic versioning. In general, all changes endeavor to be non-breaking (by moving to new names rather than by breaking existing names). COMMITS is an ever-increasing counter of commits since the beginning of this repository.

Latest release: 1.9.865

• All Released Versions

deps.edn dependency information:

  org.clojure/core.async {:mvn/version "1.9.865"}

Leiningen dependency information:

 [org.clojure/core.async "1.9.865"]

Maven dependency information:

<dependency>
  <groupId>org.clojure</groupId>
  <artifactId>core.async</artifactId>
  <version>1.9.865</version>
</dependency>

Contributing

Contributing to Clojure projects requires a signed Contributor Agreement. Pull requests and GitHub issues are not accepted; please use the core.async JIRA project to report problems or enhancements.

To run the ClojureScript tests:

• lein cljsbuild once
• open script/runtests.html
• View JavaScript console for test results

License

Distributed under the Eclipse Public License, the same as Clojure.

Copyright © Rich Hickey and contributors

Changelog

• Release 1.10.870-alpha2 on 2026-04-06
  • ASYNC-275 (CLJ) Fixed flow/futurize to retain original behavior of propagating exceptions
• Release 1.10.864-alpha1 on 2026-03-19
  • Alpha release of core.async.flow - all APIs subject to change
  • ASYNC-274 (CLJ) Fixed flow/futurize stopped returning a future on Executor change
  • ASYNC-270 (CLJ) futurize with no :exec arg throws
• Release 1.9.865 on 2026-03-19 (accumulated changes since 1.8.741)
  • Added datafy support for channels and buffers
  • ASYNC-273 (CLJ) alts!! callbacks should dispatch on caller when possible
  • ASYNC-272 (CLJ) Use JVM virtual threads in io-thread
  • ASYNC-269 (CLJ) Noop callbacks dispatch on caller thread
• Release 1.9.859-alpha4 on 2026-03-16
  • ASYNC-273 (CLJ) alts!! callbacks should dispatch on caller when possible
  • ASYNC-274 (CLJ) Fixed flow/futurize stopped returning a future on Executor change
  • ASYNC-270 (CLJ) futurize with no :exec arg throws
• Release 1.9.847-alpha3 on 2026-03-11
  • Flow - first cut of broadcast system
  • ASYNC-262 (CLJ) REVERTED from 1.9.829-alpha2
  • ASYNC-272 (CLJ) Use JVM virtual threads in io-thread
  • ASYNC-269 (CLJ) Noop callbacks dispatch on caller thread
• Release 1.9.829-alpha2 on 2025-10-01
  • ASYNC-262 (CLJ) Use virtual threads when available for go and io-thread
• Release 1.9.808-alpha1 on 2025-04-28
  • First alpha release of core.async.flow - all APIs subject to change
  • Added datafy support for channels and buffers
• Release 1.8.741 on 2025-04-07
  • ASYNC-234 (CLJ) Inactive alt handlers hold strong references to (potentially large) caller state after the alt completes
• Release 1.8.735 on 2025.04.02
  • Fix reflection warnings when using clojure.core.async.go-checking
• Release 1.8.730 on 2025.04.02, effective changes since last non-beta release:
  • ASYNC-256 (CLJ) Add io-thread and System property clojure.core.async.executor-factory
  • ASYNC-260 (CLJ) Remove now unused property clojure.core.async.pool-size
  • ASYNC-255 (CLJ) alts guards against put of nil message on entry
• Release 1.8.726-beta3 on 2025.03.31
  • ASYNC-259 (CLJ) Update clojure.core.async.go-checking with new executor pools
• Release 1.8.718-beta2 on 2025.03.10
  • ASYNC-259 (CLJ) Implement clojure.core.async.go-checking with new executor pools
  • ASYNC-260 (CLJ) Remove now unused property clojure.core.async.pool-size
  • ASYNC-261 (CLJ) Put clojure.core.async/thread-macro-executor var back into place
• Release 1.8.711-beta1 on 2025.02.19
  • ASYNC-256 (CLJ) Add io-thread and System property clojure.core.async.executor-factory
  • ASYNC-255 (CLJ) alts guards against put of nil message on entry
  • Update tools.analyzer.jvm to 1.3.2
• Release 1.7.701 on 2024.12.17
  • ASYNC-254 (CLJ) Completions for blocking ops can be directly delivered without enqueuing for dispatch
  • ASYNC-252 (CLJ) Move go expander from ioc-macros to impl.go namespace
  • ASYNC-246 (CLJ) Fix non-deterministic test
  • Update deps to latest
• Release 1.6.681 on 2023.08.09
  • Revert ASYNC-248 (CLJ) due to the issues in ASYNC-249
  • Update to tools.analyzer.jvm 1.2.3
• Release 1.6.673 on 2022.10.27
  • ASYNC-248 (CLJ) Dynamically load ioc analyzer only when needed
  • Perf improvements in go macro compilation
  • Note: as of this version, core.async requires Clojure 1.10
• Release 1.5.648 on 2021.12.14
  • Update dep for tools.analyzer.jvm to 1.2.2
• Release 1.5.644 on 2021.12.06
  • Update dep for tools.analyzer.jvm to 1.2.1
• Release 1.5.640 on 2021.11.23
  • ASYNC-204 (both) On put to closed channel, commit handler to allow pending alt ops to be cleaned up
  • ASYNC-235 (both) Fix ioc-macros/return-chan registers a callback with incorrect arity
  • ASYNC-144 (both) Tweak docstring in pipeline-async
  • ASYNC-238 (both) Fix a/map with empty chan vector hangs
• Release 1.4.627 on 2021.11.03
  • ASYNC-132 (CLJS) Can't close over locals in #js in go)
  • ASYNC-117 (CLJS) let-bindings unavailable in #js literals in go-blocks
  • Update dep for tools.analyzer.jvm to 1.2.0
• Release 1.3.618 on 2021.04.26
  • ASYNC-237 (CLJS) timeout timers access array elements with out-of-bounds index
• Release 1.3.610 on 2020.07.24
  • Update dep for tools.analyzer.jvm to 1.1.0
• Release 1.2.603 on 2020.05.11
  • Fix bug in cljs impl of onto-chan! in 1.2.598
• Release 1.2.598 on 2020.05.11
  • Add onto-chan! and to-chan! to cljs core.async
• Release 1.2.593 on 2020.05.11
  • onto-chan use of go-loop incompatible with blocking colls, replace with onto-chan! and onto-chan!!
• Release 1.1.587 on 2020.04.01
  • Added :require-macros for the promise interop from 1.1.582
• Release 1.1.582 on 2020.03.31
  • Bumped deps - clojure 1.9, clojurescript 1.10.1.597, cljsbuild 1.1.7, tools.analyzer.jvm 1.0.0
  • ASYNC-165 (CLJS) Fix inlining of let binding
  • ASYNC-184 (CLJS) Port CLJ exception handling fixes
  • ASYNC-228 (CLJS) Fix skip list for CLJS timers
  • ASYNC-96 (CLJS) Fix full checking in fixed buffer
  • ASYNC-230 (CLJS) Add js/Promise interop via core.async.interop
• Release 1.0.567 on 2020.02.18
• Release 0.7.559 on 2020.01.10
  • ASYNC-198 (CLJ) Fix exception rewriting in go can replace return value
  • ASYNC-220 (CLJ) Fix exception in go finally swallows exception of outer try
  • ASYNC-229 (CLJ) Fix go finally block executed twice
  • ASYNC-212 (CLJ) Fix go fails to compile expressions with literal nil as let value
  • ASYNC-145 (CLJ, CLJS) Fix mix throws error when many channels added
  • ASYNC-170 (CLJ) Fix binding in go block throws assertion error
  • ASYNC-127 (CLJ, CLJS) Fix mult to work as doc'ed with all taps accepting before next
  • ASYNC-210 (CLJ) Fix puts allowed when buffer still full from expanding transducer
• Release 0.6.532 on 2019.12.02
  • Bump tools.analyzer.jvm dep to 0.7.3
• Release 0.5.527 on 2019.11.12
  • Add system property clojure.core.async.go-checking that will throw if core.async blocking ops (>!!, <!!, alts!!, alt!!) are used in a go block
  • Fix use of blocking op and thread constraints in pipeline - will now match pipeline-blocking in using N cached threads.
• Release 0.4.500 on 2019.06.11
  • ASYNC-227 cljs alts! isn't non-deterministic
  • ASYNC-224 Fix bad putter unwrapping in channel abort
  • ASYNC-226 Fix bad cljs test code
• Release 0.4.490 on 2018.11.19
  • ASYNC-216 Delay start of timeout thread
  • ASYNC-218 Fix docstring for put!
  • ASYNC-213 Small addition to promise-chan docstring
• Release 0.4.474 on 2018.01.08
  • Fix typo in error message
  • Remove Java code, depend on Java 1.7+
  • Add deps.edn, can now be used as a git dependency
• Release 0.3.465 on 2017.11.17
  • ASYNC-119 Move macros to cljs.core.async ns (CLJS)
  • ASYNC-201 Out-of-bounds index values passed in timers (CLJS)
• Release 0.3.443 on 2017.05.26
  • ASYNC-159 - promise-chan in ClojureScript is broken
• Release 0.3.442 on 2017.03.14
  • Fix bad :refer-clojure clause that violates new spec in Clojure 1.9.0-alpha15
• Release 0.3.441 on 2017.02.23
  • ASYNC-187 - Tag metadata is lost in local closed over by a loop
    • Related: ASYNC-188
  • ASYNC-185 - thread prevents clearing of body locals
  • ASYNC-186 - NPE when go closes over a local variable bound to nil
• Release 0.3.426 on 2017.02.22
  • ASYNC-169 - handling of catch and finally inside go blocks was broken, causing a number of issues. Related: ASYNC-100, ASYNC-173, ASYNC-180, ASYNC-179, ASYNC-122, ASYNC-78, ASYNC-168
  • ASYNC-138 - go blocks do not allow closed over locals to be cleared which can lead to a memory leak. Related: ASYNC-32
  • ASYNC-155 - preserve loop binding metadata when inside a go block
  • ASYNC-54 - fix bad type hint on MAX-QUEUE-SIZE
  • ASYNC-177 - fix typo in Buffer protocol full? method
  • ASYNC-70 - docstring change in thread, thread-call
  • ASYNC-143 - assert that fixed buffers must have size > 0
  • Update tools.analyzer.jvm dependency
• Release 0.2.395 on 2016.10.12
  • Add async version of transduce
• Release 0.2.391 on 2016.09.09
  • Fix redefinition warning for bounded-count (added in Clojure 1.9)
  • Add :deprecated meta to the deprecated functions
• Release 0.2.385 on 2016.06.17
  • Updated tools.analyzer.jvm version
• Release 0.2.382 on 2016.06.13
  • Important: Change default dispatch thread pool size to 8.
  • Add Java system property clojure.core.async.pool-size to set the dispatch thread pool size
  • ASYNC-152 - disable t.a.jvm's warn-on-reflection pass
• Release 0.2.374 on 2015.11.11
  • ASYNC-149 - fix error compiling recur inside case in a go block
  • Updated tools.analyzer.jvm version (and other upstream deps)
  • Updated to latest clojurescript and cljsbuild versions
• Release 0.2.371 on 2015.10.28
  • ASYNC-124 - dispatch multiple pending takers from expanding transducer
  • ASYNC-103 - NEW promise-chan
  • ASYNC-104 - NEW non-blocking offer!, poll!
  • ASYNC-101 - async/reduce now respects reduced
  • ASYNC-112 - replace "transformer" with "transducer" in deprecation messages
  • ASYNC-6 - alts! docs updated to explicitly state ports is a vector
  • Support (try (catch :default)) in CLJS exception handling
  • Use cljs.test
  • Updated tools.analyzer.jvm version (and other upstream deps)
• Release 0.1.346.0-17112a-alpha on 2014.09.22
  • cljs nextTick relies on goog.async.nextTick
  • Updated docstring for put! re result on closed channel
• Release 0.1.338.0-5c5012-alpha on 2014.08.19
  • Add cljs transducers support
• Release 0.1.319.0-6b1aca-alpha on 2014.08.06
  • Add transducers support
  • NEW pipeline
• Release 0.1.303.0-886421-alpha on 2014.05.08
• Release 0.1.301.0-deb34a-alpha on 2014.04.29
• Release 0.1.298.0-2a82a1-alpha on 2014.04.25
• Release 0.1.278.0-76b25b-alpha on 2014.02.07
• Release 0.1.267.0-0d7780-alpha on 2013.12.11
• Release 0.1.262.0-151b23-alpha on 2013.12.10
• Release 0.1.256.0-1bf8cf-alpha on 2013.11.07
• Release 0.1.242.0-44b1e3-alpha on 2013.09.27
• Release 0.1.222.0-83d0c2-alpha on 2013.09.12