Attempting to use GraalVM and Kotlin coroutines together fails due to a limitation of GraalVM - it cannot handle some perfectly valid bytecode produced by the Kotlin compiler.

Kraal performs "node splitting" on Java bytecode in order to eliminate the irreducible loops produced by the Kotlin compiler that GraalVM doesn't handle. The result is a functionally-equivalent bytecode which can be successfully processed with GraalVM.

Eventually, GraalVM may support irreducible loops, or the Kotlin compiler may add a flag to produce bytecode without them. Until then, Kraal allows the usage of these two technologies together.

• oracle/graal#366

Using the Kotlin DSL:

plugins {
    id("com.hpe.kraal") version "0.0.15"
}

The Kraal Gradle plugin by default takes all jars produced by the build and their runtime dependencies, processes them to remove irreducible loops, and leaves processed copies of the jars under build/kraal.

The kraal extension is provided for convenient configuration of the default execution of KraalTask:

kraal {
    input = files(...) // *replace* set of input files
    from(...)          // or, *add* to set of input files

    outputDirectory = file(...)
}

The task and extension expose properties that create a Provider of a zipTree of the processed versions of all of the files. This can be used as a convenient way to create a "fat jar" of the processed classes:

val fatjar by tasks.creating(Jar::class) {
    from(kraal.outputZipTrees) {
        exclude("META-INF/*.SF")
        exclude("META-INF/*.DSA")
        exclude("META-INF/*.RSA")
    }
}

See the example directory for a complete working example with Ktor and GraalVM.

Use the exec-maven-plugin to execute the Kraal driver application com.hpe.kraal.MainKt:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>exec-maven-plugin</artifactId>
    <version>1.6.0</version>
    <dependencies>
        <dependency>
            <groupId>com.hpe.kraal</groupId>
            <artifactId>kraal</artifactId>
            <version>0.0.15</version>
        </dependency>
    </dependencies>
    <executions>
        <execution>
            <goals>
                <goal>java</goal>
            </goals>
            <phase>package</phase>
            <configuration>
                <mainClass>com.hpe.kraal.MainKt</mainClass>
                <arguments>
                    <argument>${project.build.directory}/${project.build.finalName}.${project.packaging}</argument>
                </arguments>
                <includePluginDependencies>true</includePluginDependencies>
            </configuration>
        </execution>
    </executions>
</plugin>

See the maven-example directory for a complete working example with Ktor and GraalVM.