Clojure: core.async and Virtual Threads

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A new Clojure blog post/announcement has been posted!

core.async 1.9.829-alpha2 is now available, which adds support for Java virtual threads (ASYNC-262).

Threads must block while waiting on I/O operations to complete. "Parking" allows the platform to unmount and free the underlying thread resource while waiting. This allows users to write "normal" straight line code (without callbacks) while consuming fewer platform resources. Clojure core.async go blocks until now used an analyzer to rewrite code with inversion of control specifically for channel parking operations (the ! async ops like >!). Other blocking operations (!! channel ops or arbitrary I/O ops) are not allowed.

Since Java 21, virtual threads implement I/O parking in the Java platform itself - that capability is a superset of what go blocks provide by supporting all blocking I/O operations. Because virtual threads are a superset of go block capabilities, go blocks can now be reimplemented using virtual threads without changing their semantics.

Using virtual threads

This release reimplements go blocks using virtual threads when available (Java 21+). go blocks retain their existing semantics (! channel ops park, blocking I/O not allowed) but do not require loading or running the analyzer. core.async is faster to load (when using Clojure >= 1.12.3) and faster to compile go blocks (no IOC). No code or configuration changes are required.

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Get the full details here: Clojure - core.async and Virtual Threads