Ahead-of-Time Compilation of Java and Polyglot Applications

These are sample applications illustrating GraalVM unique capabilities to create self-contained executable images which can run unbelievably fast. Here you can find also a more sophisticated example showing the possibility to create polyglot native images.

Preparation #

1. Download or clone the repository and navigate into the native-list-dir directory:

git clone https://github.com/graalvm/graalvm-demos
cd graalvm-demos/native-list-dir

There are two Java classes, but we will start by building ListDir.java for the purposes of this demo. You can manually execute javac ListDir.java, there is also a build.sh script included for your convenience. Note that you can use any JDK for compiling the Java classes, however we refer to javac from GraalVM in the build script to simplify the prerequisites and not to depend on another JDK installed.

2. Having installed GraalVM, export the home directory as the $GRAALVM_HOME and add $GRAALVM_HOME/bin to the path, using a command-line shell for Linux:

export GRAALVM_HOME=/home/${current_user}/path/to/graalvm

and for macOS:

export GRAALVM_HOME=/Users/${current_user}/path/to/graalvm/Contents/Home

Note that your paths are likely to be different depending on the download location.

3. Install Native Image to make use of the native-image utility.

4. Then execute:

./build.sh

The build.sh script creates a native image from the Java class.

Look at it in more detail:

$GRAALVM_HOME/bin/native-image ListDir

The native-image utility ahead-of-time compiles the ListDir class into a standalone binary in the current working directory. After running the command, an executable file listdir should have been produced.

Running the Application #

To run the application, you need to either execute the ListDir class, as a normal Java application using java, or, since we have a native image prepared, run that directly.

The run.sh file, executes both, and times them with the time utility.

time java ListDir $1
time ./listdir $1

To make it more interesting, pass it to a parent directory: ./run.sh .. (.. - is the parent of the current directory, the one containing all the demos).

Depending on the directory content you pass this script for, the output will be different than this:

java ListDir ..
Walking path: ..
Total: 141 files, total size = 14448801 bytes

real	0m0.320s
user	0m0.379s
sys	0m0.070s
./listDir ..
Walking path: ..
Total: 141 files, total size = 14448801 bytes

real	0m0.030s
user	0m0.005s
sys	0m0.011s

The performance gain of the native version is largely due to the faster startup.

Polyglot Capabilities #

You can also experiment with a more sophisticated ExtListDir example, which uses Java and JavaScript polyglot capabilities.

To compile that class you need to add graal-sdk.jar on the classpath:

$GRAALVM_HOME/bin/javac -cp $GRAALVM_HOME/jre/lib/boot/graal-sdk.jar ExtListDir.java

Building the native image command is similar to the one above, but, since the example uses JavaScript, you need to inform the native-image utility about it by passing the --language:js option. Note that it takes a bit more time because it needs to include the JavaScript support.

$GRAALVM_HOME/bin/native-image --language:js ExtListDir

The execution is the same as in the previous example:

$ time java ExtListDir $1
$ time ./extlistdir $1

Profile-Guided Optimizations for High Throughput #

Oracle GraalVM Enterprise Edition offers extra benefits for building native images. These are profile-guided optimisations (PGO). As an example, a program demonstrating Java streams will be used.

1. Run the application with java to see the output:

javac Streams.java
$GRAALVM_HOME/bin/native-image Streams
./streams 1000000 200
...
Iteration 20 finished in 1955 milliseconds with checksum 6e36c560485cdc01

2. Building an instrumented image and run it to collect profiles:

$GRAALVM_HOME/bin/native-image --pgo-instrument Streams
./streams 1000 200

Profiles collected from this run are now stored in the default.iprof file. Note that you run the profiling with a much smaller data size.

3. Use the profiles gathered at the previous step to build an optimized native image:

$GRAALVM_HOME/bin/native-image --pgo Streams

4. Run that optimized native image:

./streams 1000000 200
...
Iteration 20 finished in 827 milliseconds with checksum 6e36c560485cdc01

You should see more than 2x improvements in performance.