beckon-ffm

Experimental signal backends for beckon built entirely on the Java Foreign Function & Memory API (JDK 22+), as an alternative to beckon's default sun.misc.Signal backend:

• Linux - signalfd(2)
• macOS / BSD - kqueue(2) with EVFILT_SIGNAL

It exists because sun.misc.Signal is an internal JDK API that may eventually be removed; this proves out the supported modern replacement. It is experimental and shipped separately precisely because it needs JDK 22+, while beckon's core jar targets JDK 8.

Usage

Add both beckon and beckon-ffm, then opt in with a system property.

[net.clojars.savya/beckon "0.4.0"]
[net.clojars.savya/beckon-ffm "0.1.0"]

Run the JVM with:

-Dbeckon.signal.backend=ffm --enable-native-access=ALL-UNNAMED

The right native mechanism is selected automatically for the platform. The beckon API is unchanged - see the beckon README.

Capabilities and limits

The two implementations differ, which is instructive:

• Linux (signalfd) reliably handles beckon's own raise!, but not signals from outside the process (e.g. kill -HUP): a JVM starts threads before beckon loads, and signalfd only captures a signal blocked in every thread, which cannot be arranged retroactively.
• macOS/BSD (kqueue) sets each managed signal to SIG_IGN - a process-wide disposition - so it also observes external signals.

Because of the Linux limitation and JEP 472 native-access restrictions (--enable-native-access, denied by default from JDK 26), this is not a drop-in replacement; sun.misc.Signal remains beckon's default.

Compatibility

Requires JDK 22 or later (Foreign Function & Memory API, JEP 454). Linux and macOS/BSD only. Continuously tested on JDK 25 across Ubuntu and macOS.

License

Copyright © 2026 Savyasachi.

A companion to beckon (originally by Jean Niklas L'orange). Distributed under the Eclipse Public License, the same as Clojure.