graal-build-time

From GraalVM 22 onwards, the native-image global --initialize-at-build-time option will be deprecated. This means you will have to list every package that you want to initialize at build time separately, like initialize-at-build-time=clojure,my_library. Classes created by Clojure (currently) need to be initialized at build time. This library automatically registers classes created by Clojure as such, so you don't have to.

Usage

For you native-image build:

1. If you are using a global --initialize-at-build-time, remove it.
2. Include this library on your classpath. This is typically done by simply adding this library to your project dependencies (see clojars link above).

During the image build, you will see a line of output like:

[clj-easy/graal-build-time] Registering packages for build time initialization: clojure, clj_easy

How does it work

This library inspects the classpath during a native image build. All classes that end with __init.class are assumed to be created by Clojure. The package of that class is then added to the results.

Overriding classes

If there are classes in packages that you would like to override, you can still use the --initialize-at-run-time=my.org.MyClass argument in your build. E.g. when using http-kit, the org.httpkit package is included for build-time initialization, but you will still need to override one class: --initialize-at-run-time=org.httpkit.client.ClientSslEngineFactory$SSLHolder.

Single segment namespaces

This library doesn't work with single segment namespaces like digest in a file like src/digest.clj. We recommend not using single segment namespaces in libraries.

Develop

Run bb tasks for all relevant project tasks.

Tasks attempt to avoid unnecessary work by comparing source and target file dates. If you want to skip this optimization, run bb clean before running your task.

Use bb native-image-test to run our integration tests.

• This task builds native images for a hello world app, and then runs them.

• The hello world sources are compiled to Java classes and then jarred to an uberjar.

• We use GraalVM's native-image with graal-build-time on the classpath to create 2 variants of the same app:

  • one built from the uberjar
  • the other built directly from the classes dir

• Note that we omit --initialize-at-build-time when creating the native images. The work that this deprecated option carried out is now taken care of by graal-build-time.

• During native image creation, you'll see output that looks like this:

  [target/native-test-classes:34725]    classlist:   1,627.53 ms,  0.96 GB
  [target/native-test-classes:34725]        (cap):   1,892.39 ms,  0.96 GB
  [clj-easy/graal-build-time] WARN: Single segment package found for class: single_segment_example__init.class. This class has no package and it will not be added to the result packages.
  [clj-easy/graal-build-time] Registering packages for build time initialization: clojure, graal_build_time_test, graal_build_time_test_app, clj_easy
  [target/native-test-classes:34725]        setup:   3,885.01 ms,  0.96 GB
  [target/native-test-classes:34725]     (clinit):     219.91 ms,  1.74 GB
  

  Note:

  • [clj-easy/graal-build-time] Registering packages for build time initialization... will always appear
  • [clj-easy/graal-build-time] WARN: Single segment package found... will appear to warn you of the repercussions of a compiled Clojure single segment namespace found in your build.

License

Licensed under the MIT license, see LICENSE.

Copyright © 2021 Michiel Borkent, Eric Dallo, Rahul Dé, Lee Read and contributors.