Helps GraalVM's native-image-agent to be more useful for Clojure applications.
Because Clojure does lots of reflection and bytecode generation when a namespace is loaded, it's necessary to
use build-time initialization
for all Clojure namespaces when compiling it with GraalVM Native Image. We would like native-image-agent to not report
about the reflection and resource usages that happen during Clojure namespace loading. Also we would like to generate
the correct list of classes to put in --initialize-at-build-time, i.e. all Clojure namespaces and the Java classes
which were used during Clojure namespace loading.
That's where this Java agent comes in. You give it the main class of your Clojure application as a parameter, and it
will initialize the Clojure namespaces and track all classes that were loaded, before letting native-image-agent do
its thing. As a result, you get a list of classes to --initialize-at-build-time, and the configuration files generated
by native-image-agent will be shorter.
Download clojure-native-image-agent.jar from releases.
Run clojure-native-image-agent.jar as a Java agent together with native-image-agent.
The order of command line parameters matters: clojure-native-image-agent.jar must be before native-image-agent
on the command line, so that it will run first.
/usr/bin/java \
-javaagent:clojure-native-image-agent.jar=initialize-class=your_clojure_app.main,output-dir=/tmp/native-image \
-agentlib:native-image-agent=config-merge-dir=/tmp/native-image,config-write-period-secs=5 \
-jar your-clojure-app.jar
This will generate a native-image.properties configuration file in the output-dir directory, based on the classes
that were loaded during the initialization of initialize-class.
The configuration is simplified for Clojure namespaces, so that only the top level package is listed. Most JDK classes
are excluded from the configuration, because GraalVM Native Image already handles those. The unredacted list of classes
is written to initialized-classes.txt for debugging purposes.
Currently, the agent initializes all classes that were loaded during initialization. But the Clojure compiler also loads
some classes (Java libraries) without initializing them. Excluding those classes from --initialize-at-build-time would
reduce the risk of encountering incompatible classes.
Build target/clojure-native-image-agent.jar
mvn clean package