Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/vmencik/akka-graal-native

Example of Akka HTTP server compiled with GraalVM native-image
https://github.com/vmencik/akka-graal-native

Last synced: about 1 month ago
JSON representation

Example of Akka HTTP server compiled with GraalVM native-image

Awesome Lists containing this project

README 

        
# Akka HTTP + GraalVM native

Example project with simple Akka HTTP server compiled with GraalVM native-image.



## Pre-requisites

  * SBT

  * [GraalVM](https://github.com/oracle/graal/releases)

  * `native-image` from `GRAAL_HOME/bin` in `PATH`

  

Suggested environment variables:



    export GRAAL_HOME=/Library/Java/JavaVirtualMachines/graalvm-ce-19.1.1/Contents/Home

    export PATH=$PATH:${GRAAL_HOME}/bin

    

[Install native-image](https://www.graalvm.org/docs/reference-manual/aot-compilation/#install-native-image):



    gu install native-image

  

## Compiling

    

    sbt graalvm-native-image:packageBin

    

It might take a few minutes to compile.

   

## Running

    

    # MacOS:

    ./target/graalvm-native-image/akka-graal-native -Djava.library.path=${GRAAL_HOME}/jre/lib

    

    # Linux:

    ./target/graalvm-native-image/akka-graal-native -Djava.library.path=${GRAAL_HOME}/jre/lib/amd64

    

Because the project is compiled with

[Java Crypto enabled](https://github.com/oracle/graal/blob/master/substratevm/JCA-SECURITY-SERVICES.md)

for the native image (to support HTTPS) `java.library.path` system property must be set at runtime

to point to a directory where the dynamic library for the SunEC provider is located.



After the server starts you can access [http://localhost:8086/graal-hp-size](http://localhost:8086/graal-hp-size)

which will make an HTTPS request to the GraalVM home page using Akka HTTP client and return the size of the response.



## How it works

Most of the Akka-specific configuration for `native-image` is provided by [akka-graal-config](https://github.com/vmencik/akka-graal-config)

repository which publishes a set of jar artifacts that contain the necessary configuration resources

for `native-image` to compile Akka modules. Just having these jars in the classpath is enough

for `native-image` to pick up this configuration.

See [this blog post](https://medium.com/graalvm/simplifying-native-image-generation-with-maven-plugin-and-embeddable-configuration-d5b283b92f57)

for more details on how that mechanism works.



### Reflection configuration

See [SubstrateVM docs](https://github.com/oracle/graal/blob/master/substratevm/REFLECTION.md)

for details.



Configuration for Akka itself is provided by [akka-graal-config](https://github.com/vmencik/akka-graal-config)

dependencies. This repo contains only reflection configuration to get java.util.logging working.



Note however that reflective access to `context` and `self` fields must be configured for every actor

that is monitored with `context.watch` (observed empirically).

Otherwise you'll get [an error from Akka's machinery](https://github.com/akka/akka/blob/v2.5.21/akka-actor/src/main/scala/akka/actor/ActorCell.scala#L711).



### HTTPS

Passing the `--enable-url-protocols=https` option to `native-image` enables JCE features.

This configuration option is enabled by configuration from `graal-akka-http` dependency.



### Affinity Pool

`akka.dispatch.affinity.AffinityPool` is using MethodHandles which causes errors like this one

during native image build:



    Error: com.oracle.graal.pointsto.constraints.UnsupportedFeatureException: Invoke with MethodHandle argument could not be reduced to at most a single call: java.lang.invoke.MethodHandle.bindTo(Object)

    

The workaround is to initialize affected classes (and we actually do this for the whole classpath)

at build time using the `--initalize-at-build-time` option.



### Lightbend Config

Static initializers of `com.typesafe.config.impl.ConfigImpl$EnvVariablesHolder`

and `com.typesafe.config.impl.ConfigImpl$SystemPropertiesHolder` need to be run at runtime using

the `--initialize-at-run-time` option.

Otherwise the environment from image build time will be baked in to the configuration.



### Akka Scheduler and sun.misc.Unsafe

To make the default Akka scheduler work with SubstrateVM it is necessary to recalculate the field

offset that it uses with sun.misc.Unsafe.

This is done by using SubstrateVM API in `AkkaSubstitutions` class from `graal-akka-actor` dependency.



For more details see the section about Unsafe in this [blog post](https://medium.com/graalvm/instant-netty-startup-using-graalvm-native-image-generation-ed6f14ff7692).



Note that this substitution is only necessary with Scala 2.12. Curiously with Scala 2.13 `native-image`

can make the substitution itself automatically. Probably due to some difference in the emitted

bytecode.



### MethodHandle in scala.runtime.Statics

In Scala 2.13 a MethodHandle is used in `Statics.releaseFence()` to invoke either

`java.lang.invoke.VarHandle.releaseFence()` if running in Java 9 VM or `sun.misc.Unsafe.storeFence()`

if on Java 8. As noted above, MethodHandles are a problem with `native-image` but since GraalVM is

currently based on Java 8 `Statics.releaseFence()` can be substituted to always call Unsafe without

using MethodHandle. This is done by `ScalaSubstitutions` present in Scala 2.13 version of

`graal-akka-actor`.



### Serialization

SubstrateVM does not support Java serialization yet so anything that depends on

`akka.serialization.JavaSerializer` will not work with `native-image`.



### Logging

It is currently not easy to get Logback working because of its Groovy dependencies and incomplete

classpath problems with `native-image` so `java.util.logging` is used instead.