GraalVM Native Image

Cats Effect 3.3.0 brought support for printing a fiber dump to the standard error stream. This functionality can be triggered using POSIX signals. Unfortunately, due to the sun.misc.Signal API being an unofficial JDK API, in order to achieve maximum compatibility, this functionality was implemented using the java.lang.reflect.Proxy reflective approach.

Luckily, GraalVM Native Image has full support for both Proxy and POSIX signals. Cats Effect jars contain extra metadata that makes building native images seamless, without the need of extra configuration. The only caveat is that this configuration metadata is specific to GraalVM 21.0 and later. Previous versions of GraalVM are supported, but Native Image support requires at least 21.0.

Native Image example

Here's an example of an Hello world project compiled with GraalVM Native Image using sbt-native-image plugin.

// project/plugins.sbt
addSbtPlugin("org.scalameta" % "sbt-native-image" % "0.3.1")

// build.sbt
ThisBuild / organization := "com.example"
ThisBuild / scalaVersion := "2.13.8"

lazy val root = (project in file(".")).enablePlugins(NativeImagePlugin).settings(
  name                := "cats-effect-3-hello-world",
  libraryDependencies += "org.typelevel" %% "cats-effect" % "3.4.6",
  Compile / mainClass := Some("com.example.Main"),
  nativeImageOptions  += "--no-fallback",
  nativeImageVersion  := "22.1.0" // It should be at least version 21.0.0
)

// src/main/scala/com/example/Main.scala
package com.example

import cats.effect.{IO, IOApp}

object Main extends IOApp.Simple {
  def run: IO[Unit] = IO.println("Hello Cats Effect!")
}

Note: nativeImageOptions += "--no-fallback" is required, otherwise native-image will try searching a static reflection configuration for this Enumeration method. Thus using this flag is safe only if you're not using Enumerations in your codebase, see this comment for more info.

The code can be compiled using sbt nativeImage and a native-image executable can then be found under target/native-image/cats-effect-3-hello-world, and executed as any native executable with the benefit of a really fast startup time (hyperfine is a command line benchmarking tool written in Rust)

$ ./target/native-image/cats-effect-3-hello-world
Hello Cats Effect!

$ hyperfine ./target/native-image/cats-effect-3-hello-world
Benchmark 1: ./target/native-image/cats-effect-3-hello-world
  Time   (mean ± σ):    11.2 ms ±   0.6 ms    [User: 6.7 ms, System: 4.8 ms]
  Range (min … max):     9.4 ms …  12.9 ms    182 runs

Another way to get your cats effect app compiled with native-image is to leverage the package command of scala-cli, like in the example