Clojure-CLI-CRaC

A drop-in Clojure-CLI replacement that gets you to the REPL fast.

Clojure is known for its slow start. This project utilizes Linux's Checkpoint/Restore functionality to cache JVM state to disk after Clojure finishes initialization. Subsequent Clojure launches are much faster by restoring from the cached state.

Read more about the design process: part 1 part 2.

Installation

Clojure-CLI-CRaC requires bash and rlwrap. It can be used alongside the offical Clojure CLI.

Clone this repo

git clone https://github.com/YizhePKU/Clojure-CLI-CRaC.git

Download the latest build of JDK with CRaC. Unpack with sudo (sudo is necessary because it contains a setuid executable for triggering Checkpoint/Restore)

wget https://github.com/CRaC/openjdk-builds/releases/download/17-crac%2B5/openjdk-17-crac+5_linux-x64.tar.gz
sudo tar xf openjdk-17-crac+5_linux-x64.tar.gz

Move the unpacked directory into this repo. Rename it to openjdk-17-crac

sudo mv openjdk-17-crac+5_linux-x64 Clojure-CLI-CRaC/openjdk-17-crac

(Optional) add the bin/ directory to your PATH

Usage

Clojure-CLI-CRaC is a drop-in Clojure CLI replacement. Run clojure and clj as you normally would.

JVM options can only be set on the first launch (otherwise they have no effect)
Will automatically invalidate the checkpoint when deps.edn changes (e.g. new dependencies)

Limitations and known issues

Currently Linux-x86_64 only
Will print a bunch of nonsense when creating a checkpoint
There's currently an upstream bug that causes whitespace in command line arguments to be misinterpreted