beckon-ffm

Experimental signal backends for beckon use only the Java Foreign Function & Memory API (JDK 22+). Use them as an alternative to beckon's default sun.misc.Signal backend:

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

sun.misc.Signal is an internal JDK API. The JDK can remove it. This library tests a supported replacement. It is experimental and ships separately because it requires JDK 22+. The beckon core jar targets JDK 8.

Stack

Installation

Use beckon by default. Add beckon-ffm only when you want the experimental Foreign Function & Memory backend and can run on JDK 22+.

Add both artifacts, then opt in with a system property.

net.clojars.savya/beckon {:mvn/version "0.4.2"}
net.clojars.savya/beckon-ffm {:mvn/version "0.1.8"}

Leiningen:

[net.clojars.savya/beckon "0.4.2"]
[net.clojars.savya/beckon-ffm "0.1.8"]

Run the JVM with:

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

The platform selects the native mechanism automatically. The beckon API does not change. See the beckon README.

Capabilities and limits

The two implementations differ:

• Linux (signalfd) reliably handles beckon's own raise!. It does not reliably handle signals from outside the process (e.g. kill -HUP). A JVM starts threads before beckon loads. signalfd only captures a signal blocked in every thread. beckon cannot arrange this after the JVM starts.
• macOS/BSD (kqueue) sets each managed signal to SIG_IGN. This is a process-wide disposition. It also observes external signals.

The Linux limitation and JEP 472 native-access restrictions mean this is not a drop-in replacement. --enable-native-access is denied by default from JDK 26. sun.misc.Signal remains beckon's default.

Compatibility

Requires JDK 22 or later (Foreign Function & Memory API, JEP 454). Linux and macOS/BSD only. CI compiles and tests on JDK 22.

Development

Use JDK 22. Compile the two Java FFM backends before running the test suite:

clojure -T:build compile-java
clojure -M:test
clojure -T:build jar

License

Copyright © 2026 Savyasachi.

A companion to beckon (originally by Jean Niklas L'orange). Distributed under the Eclipse Public License 1.0.