Changelog

Unreleased

0.0.3 - 2026-10-12

Performance and correctness pass across channels, the multiplexer, and the pipeline. No public API changes.

Highlights

• Allocation-free channel fast paths. put! and take! no longer allocate a closure per operation, and take! no longer allocates a result tuple or sequences it. JFR confirms the hot paths allocate no application objects.
• Arbitrary values round-trip safely. A value such as [:block ...] or :closed is returned unchanged by take!. Previously a value whose first element was :block was mistaken for an internal marker and crashed the take.
• Much faster multiplexer. The per-value virtual-thread fan-out and the per-value Phaser barrier were replaced by sequential blocking put! on the dispatcher thread. Every tap still receives every value, in order, with the same strict backpressure.
• Pipeline n=1 fix. nil is the only EOF, so boolean false now passes through, and closing the output channel stops the loop.

Compatibility

• No public API changes: protocols and function signatures are unchanged.
• Multiplexer delivery timing. Taps are now served sequentially in snapshot order rather than concurrently. Observed semantics are unchanged (all taps receive all values in order; a blocked tap blocks the mult), but the order in which different taps receive a given value is deterministic by tap snapshot position instead of racing. Code should not rely on cross-tap timing either way.
• Pipeline n=1. Boolean false inputs are no longer treated as EOF, and the loop stops when the output channel is closed.

Performance

Measured on OpenJDK 25.0.4.1, Clojure 1.12.4, on Linux; min of N runs. The multiplexer figures are an interleaved A/B against the previous revision on the same machine. Absolute numbers vary by hardware.

Channels (200k put!/take! pairs, one producer thread and one consumer):

Configuration	Before	After	Change
unbuffered	315.9 ms	315.9 ms	0%
buffered cap 5	89.7 ms	89.9 ms	~0%
buffered cap 100	32.0 ms	21.9 ms	-31%

Multiplexer (one source, buffered taps, one consumer per tap):

Configuration	Before	After	Change
dispatch-only 5 taps, 50k	140.5 ms	17.8 ms	-87%
dispatch-only 20 taps, 50k	321.8 ms	33.1 ms	-90%
full 5 taps, 100k	387.3 ms	314.2 ms	-19%
full 20 taps, 25k	274.6 ms	241.8 ms	-12%

JFR (settings=profile) shows the multiplexer hot path no longer spends time in Phaser.internalAwaitAdvance or ForkJoinPool/virtual-thread scheduling, and the channel put!/take! fast paths allocate no application objects.

Correctness is covered by the full test suite: 28 tests, 792 assertions, 0 failures.

Requirements / stack

• JDK 24 or later (tested on OpenJDK 25.0.4.1).
• Clojure 1.12.4.
• Test-only dependencies: org.clojure/core.async 1.7.701, criterium/criterium 0.4.6, circleci/bond 0.6.0, and the Cognitect test-runner v0.5.1.

Running the tests and benchmarks

# Functional tests
clojure -M:test:test-runner

# Performance benchmarks (criterium quick-bench)
clojure -M:test:test-performance

0.0.2 - 2026-07-14

Bug-fix, compatibility, and performance pass across channels, the multiplexer, the pipeline, pub/sub, and the waiter machinery. One breaking change to the pub! API.

Highlights

• Publish failure handling. pub! gained an :ex-handler for publish failures, and an exception thrown by an :ex-handler now closes the associated resources regardless of the failure. The multiplexer and pub/sub paths catch Throwable instead of Exception, so errors are reported to the handler instead of escaping the dispatch loop.
• Deadlock fixes. The pipeline no longer deadlocks when the executor rejects a job, the multiplexer error path no longer deadlocks, park-and-wait checks for interruption before its timeout check, and the multiplexer calls shutdownNow on cleanup rather than close.
• Resource-leak fixes. Executor and thread leaks in failure edge cases are fixed on both the multiplexer and pub/sub paths.
• Race fixes. Fixed an edge race between unsub-add! and sub!, and a conflict between zombied AltsWaiters and real waiters.

Compatibility

• Breaking: pub! changed arity to accept the publish functions and an :ex-handler for publish failures; update call sites accordingly.
• put! and take! return false/nil instead of :interrupted when the operation is interrupted (the channel is not closed).
• Channel implementations return nil on close!.
• pub throws when its topic function returns nil instead of silently dropping the value.

Performance

• Fast-path allocations eliminated for buffered and unbuffered channels.
• Multiplexer dispatch loop applies snapshot reuse and a single-tap fast path.
• Pipeline n=1 fast path runs on a single virtual thread.

Requirements

• JDK 24 or later.
• Clojure 1.12.4.

0.0.1 - 2026-04-12

Initial release.

Highlights

• CSP for Clojure on virtual threads. Blocking channel operations that suspend the virtual thread instead of parking a state machine, behind an explicit, macro-free API.

Added

• Unbuffered (rendezvous) and buffered channels.
• Fixed-capacity buffers.
• multiplex for fan-out with per-tap backpressure.
• Pipelines with configurable parallelism.
• Publish/subscribe via pub/sub.
• select over multiple channel operations.
• The waiter machinery and the channel, buffer, multiplexer, publisher, and selectable protocols.
• Missing functions added to the csp-clj.core namespace.

Requirements

• JDK 24 or later (for virtual thread support).
• Clojure 1.12.4.