Raspberry Pi and Scala

This is a little experience report how to bring up Scala on my RaspberryPi

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Step 1: Java

I have connected my Raspberry only with power and network (no keyboard/mouse/display) for now and log in via ssh from my Linux desktop. Not only to save cables on the desk, but also to allow copy and paste between desktop and RaspberryPi. I am running Raspbian wheezy 2012-08-16 downloaded from the Raspberry website.

Java is installed quick and easy with:

$ sudo apt-get install openjdk-7-jdk

This pulls all its prerequisites and takes a few minutes. Next I was curious to check and just took a little test program like this “hello.java”

class hello
{  
        public static void main(String args[])
        {
           System.out.println("Hello World!");
        }
}

Just compile with

$ javac hello.java

and run with

$ java hello

Curious about performance I took some measurements, first measuring the speed of compilation for a minimal program like this:

$ time javac hello

results: 14 sec. Then I tried to measure the memory size and added a sleep in the program like this:

class hello
{
  public static void main(String args[])
  {
    System.out.println("Hello World!");
    try {
      Thread.sleep(10000); // 10 sec
    } catch (Exception e) {
    }
  }
}

and run with

$ java hello &
$ ps u

Result: Virtual Size (VSZ): 215 MB, Resident Size (RSS): 9MB

Step 2: set up sbt

download with

$ wget http://scalasbt.artifactoryonline.com/scalasbt/sbt-native-packages/org/scala-sbt/sbt/0.12.0/sbt.tgz

unpack and copy to a directory of your choice I have used

$ tar tvozf sbt.tgz
$ mv sbt $HOME

The sbt directory contains a “bin” directory which needs to go in your path by adding this to your $HOME/.bashrc:

$ export PATH=$HOME/sbt/bin:$PATH

open a new shell to reload .bashrc and execute

$ sbt -mem 128 -help

you should see a help message. The parameter -mem 128 will allow 128 MB for the JVM, the default of 1536 MB is way too big for the little Raspberry Pi.

Alternatively you can put a file .sbtopts in your current directory with the sbt command line switches required, in ths case “-mem 128″.

Now, when starting

$ sbt

it will pull some files and updates, slowly, and after some minutes… The sbt prompt comes up fine.

Next I created a small “Hello world” program like this in “hello.scala”:

package greeter
object Hello extends App {
  println("Hello, World!")
}

and started with

$ sbt run

this compiles the scala and java files in your directory – this takes a fair while – and then success:

[info] Running greeter.Hello
Hello, World!
[success] Total time: 507 s, completed 16-Sep-2012 19:02:03

Wow, over 8 minutes for this little piece. But it worked.

What next?

I have seen some discussion on the web that the Oracle JVM may be faster, but also not compatible with Raspbian, so this will be a topic for further investigation. For now it looks like we have to wait for Oracle to release a compatible version, or choose another OS for Raspberry, one alternative approach using Debian Wheezy instead of Raspbian Wheezy can be found here: http://www.savagehomeautomation.com/projects/raspberry-pi-installing-oracle-java-development-kit-jdk-170u.html