GraphHopper is a fast and memory efficient Java routing engine, released under Apache License 2.0.

It runs on Android and iOS, i.e. it calculates the routes on the device without internet access. 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.

There are a couple of solutions described in this issue. And this repository is about the GraalVM option: get a native library working on Android, see the "mobile native" section.

As a side effect of this experiment we can easily create a native image with nearly no startup overhead, see the "web native" section.

# get latest graalvm from gluon https://github.com/gluonhq/client-samples/#linux-and-android
wget https://download2.gluonhq.com/substrate/graalvm/graalvm-svm-linux-20.1.0-ea+26.zip
# unzip this and let GRAALVM_HOME point to it
export GRAALVM_HOME=$BASE/graalvm-svm-linux-20.1-latest

# get Android SDK: https://developer.android.com/studio/#downloads
export ANDROID_SDK=$BASE/android-sdk-linux

# get Android NDK: https://developer.android.com/ndk/
export ANDROID_NDK=$BASE/android-sdk-linux/ndk/20.1.5948944/

cd android
mvn client:compile
mvn client:link

Then copy the produced android/target/client/aarch64-android/libgraphhoppernative.so into distribution/ghlib/arm64-v8a/ of the repository https://github.com/karussell/native-hello-world-app and start building your Android app

• 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
• cd web
• mvn clean package => should create a native image at ./target/graphhopper

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

• cd web
• download OSM road data: wget http://download.geofabrik.de/europe/germany/berlin-latest.osm.pbf -O osm.pbf
• start GraphHopper: ./target/graphhopper, see example.cpp and src/main/java/example/Example.java for the code that will be executed

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

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

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

• target iOS, see target=iOS here: https://github.com/gluonhq/client-samples and gluonhq/substrate#47
• target Android, see gluonhq/client-samples#35
• we could try to start the dropwizard web service as native image and compare e.g. performance

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:

https://github.com/oracle/graal/blob/master/substratevm/CONFIGURE.md

https://github.com/oracle/graal/blob/master/substratevm/RESOURCES.md

• 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?

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.so, 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

• installing the native-image plugin fails? Download the jar, then do bin/gu -L install ~/Downloads/native-image-installable-svm-java11-linux-amd64-19.3.0.jar
• https://www.graalvm.org/community/
• https://github.com/graalvm/graalvm-demos
• https://github.com/neomatrix369/awesome-graal
• travis example config for GraalVM
• Java distribution of native C++ libraries https://github.com/bytedeco/javacpp-presets