Skip to content
Experiments with GraphHopper: GraalVM native image execution
Java C++
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.


GraphHopper is a fast and memory efficient Java routing engine, released under Apache License 2.0. By default it uses OpenStreetMap and GTFS data, but it can import other data sources.

It runs on Android and iOS, i.e. it calculates the routes on the device without internet access. But there are a couple of problems with each approach:

  • GraphHopper mostly already works on Android but Android does not support the latest Java. Even Java 8 is not really well supported. This forces us to stay on old dependencies for our core module and also on Java7 features. Android additionally limits the area one process can mmap. This is ugly because it is an arbitrary limit at ~1.5GB hardcoded in the sources although the devices usually have more and there is no such limit for native applications.
  • There is an iOS port using j2objc, but maintaining this port is not trivial. And so this port is not up-to-date.


  • Rewrite in Kotlin that can target iOS and Android and even JavaScript. But this is a huge work and on Android one needs an additional Kotlin dependency.
  • GraalVM looks promising and could help us to develop a native library that could be included on iOS and Android.

And this repository is about the GraalVM option. Or at least to get a native library working for now on currently supported platforms like Linux.

Create Native Image for GraphHopper

  • download graalvm for your OS e.g graal CE for linux amd64, 19.3.0 and extract to graalvm/
  • run bin/gu install native-image
  • The native-image tool needs a local C toolchain: glibc-devel, zlib-devel and gcc - do e.g.sudo apt-get install zlib1g-dev
  • verify that the tool works: $JAVA_HOME/bin/native-image --help
  • set JAVA_HOME to the downloaded graal (graalvm/) to use the correct JVM for maven
  • mvn clean package => should create a native image at ./target/graphhopper

Start the GraphHopper Native Image

Now that graal created your native image you can start graphhopper:

  • download OSM road data: wget -O osm.pbf
  • start GraphHopper: ./target/graphhopper

It will take a few seconds where it basically converts the pbf file into an internal graph structure (see graph-cache folder), but all subsequent calls will be very fast and calculate the distance between two points in Berlin (see java code).

If you are finished and you noticed something is eating your CPU resources do:

$JAVA_HOME/bin/native-image --server-shutdown

Unscientific Results

Measured via command line utility time and picked the "real" time

  • OpenJDK: 0.5s
  • native image: <0.05s
  • shared library: ~0.025s

Future Tasks

  • try --static options of native-image (see --shared)
  • target iOS
  • target Android
  • we could try to start the dropwizard web service as native image and compare e.g. performance

How to make resources of dependencies working?

Run application with GraalVM and special agent:

$JAVA_HOME/bin/java -agentlib:native-image-agent=config-output-dir=./ni-configs -jar target/*-jar-with-dependencies.jar

Then include these files in native-image command line: see maven plugin.

See also:

Open Questions

  • slf4j-log4j bridge fails with ClassNotFound. Workaround: use slf4j-simple. Likely this is fixed via the resources config in previous section or maybe this
  • Why are they e.g. libgraphhopper_dynamic.h headers and how can I use --static as then no headers are created?

Call GraphHopper from C++

Instead of a native application we now want a library that is called from native code like example.cpp. To create this library do the following:

  • use <imageName>libgraphhopper</imageName> and add --shared in <buildArgs> in pom.xml
  • mvn clean package

Now you should see, libgraphhopper.h, graal_isolate.h in the ./target folder. Proceed with:

g++ example.cpp -I ./target -L ./target -lgraphhopper -o target/example
export LD_LIBRARY_PATH=./target:$LD_LIBRARY_PATH && ./target/example 52.5147 13.3
[main] INFO com.graphhopper.reader.osm.GraphHopperOSM - version 1.0|2019-11-20T22:11:41Z (5,15,4,3,5,5)
[main] INFO com.graphhopper.reader.osm.GraphHopperOSM - graph CH|car|MMAP_STORE|2D|no_turn_cost|5,15,4,3,5, details:edges:126,973(4MB), ...
Distance 6806.26

Graal Help

You can’t perform that action at this time.