Developing MagLev itself

Step 1: Install MagLev from GitHub

First, build MagLev from source as described here. Make sure to run the tests and check that they pass.

Step 2: Setup your environment

To work with MagLev from the source tree, you have to run commands from the bin directory of the repository. You can link the checkout to rbenv/.versions/maglev-head if you use rbenv, or manage your PATH in some other way. It’s important you do manage it somehow, because some commands have to be run with another Ruby’s rake, and some can be run from MagLev.

Some of the scripts and rake tasks written for developers additionally require you to set a few environment variables. So, assuming you are in the top-folder of your MagLev repository, run the following:

$ export MAGLEV_HOME="$(pwd)"
$ export GEMSTONE="$MAGLEV_HOME/gemstone"

Step 3: Building a stone from first principles

If you’ve successfully followed the build instructions, you already have a working image. But as a developer, you might run into situations where you break your stone and/or build process in one of several ways, so we’ll walk through the process of manually creating a fresh image from the Smalltalk image provided with Gemstone/S.

At each step I’ll explain what’s going on and how you might want to develop in that particular area.

Note: Most of these commands have to be run with another Ruby. MagLev by default doesn't include a script named ruby, only maglev-ruby. To avoid confusion, make sure $MAGLEV_HOME/bin is at the end of your $PATH. Whenever we have to run something with MagLev, I will always use maglev-ruby -S style invocations.

Clean everything

If at any time your image seems broken or you are afraid that some code has been persisted that you don’t know how else to remove, you can just delete the Ruby image using the clobber task.

$ rake build:clobber

Prepare the Smalltalk image

Ruby and Smalltalk run on the same VM and image, but there are a few changes that the base Smalltalk image needs in order to run even basic Ruby code. That’s the code you will find in the src/smalltalk/ruby directory. These are extensions to the core classes of the Smalltalk system, and you shouldn’t normally have to worry about those. If you ever do need to change any of them, you will have to clobber and start afresh. You can create a basic Ruby image using

$ rake build:filein

This will file in (Smalltalker speak for loading code and persisting it in an image) the basic Ruby code, as well as Monticello (a Smalltalk VCS) and the basic stuff you need to connect to the Stone from a Smalltalk image using GemTools.

If you run this task twice in succession, the second run will fail and possibly leave your image in an unusable state.

Load Ruby core

You know how, on MRI, a lot of core functionality is implemented in C? If you don’t like C, then on MagLev, the situation is a little nicer for you. While the VM, the primitives and the parser are implemented in C/C++, lots of what makes up the Ruby core library is actually written in Smalltalk. That code used to be managed in Monticello, and is now included in file-based form in src/packages. This is actually a FileTree repository, so you can still manage those packages from Monticello in GemTools.

$ rake build:packages

That invocation will load the Ruby core code (as far as it is written in Smalltalk) into the stone. If you want to develop on MagLev, you might work a lot with this code, and there’s two ways to do that:

For Smalltalkers

Developers who know either Gemstone/S or Squeak/Pharo and are comfortable working with Monticello and the image based tools should get the GemTools for MagLev.

Monticello uses FileTree to update the files whenever a new version of the Monticello package for MagLev is saved using the UI, so you don’t need to worry about keeping the code in sync. If you develop from the GemTools browser, you won’t have to repeat the build:packages command either, because all your changes are immediately persisted in your image and applied to your running code.

For friends of the text editor

You can just edit files in the src/packages directory. If you add a class, check how other classes work (separate folder for the class, json file with the definition and method names, folders for instance methods and class methods). If you need to extend a core Smalltalk class, take a look at the folders ending in .extension.

Create a stone

These last two steps have left us with an image called extent0.ruby.dbf. It’s in the fileintmp directory. Now, to create a stone, MagLev expects the image file to be in bin/, but we’ll want to be able to just run the build:packages task again to update Smalltalk code in our stones. So let’s link the image file instead:

$ ln -s $MAGLEV_HOME/fileintmp/extent0.ruby.dbf bin/extent0.ruby.dbf

Then create a stone

$ rake stone:create[maglev]

This will copy the image file to data/maglev/extent/extent0.ruby.dbf and that’s what we’ll be running off when running Ruby code. So we symlink that, too:

$ rm data/maglev/extent/extent0.ruby.dbf
$ ln -s $MAGLEV_HOME/fileintmp/extent0.ruby.dbf data/maglev/extent/extent0.ruby.dbf

Load the Ruby core

Now, finally, we can actually run some Ruby code. Nothing too serious, yet, but enough to load the other half of Ruby core written in Ruby. Much of that code was actually shared with the Rubinius project at some point in the past.

$ rake maglev:start
$ rake maglev:reload_prims

This starts the stone process and loads the code below src/kernel. That means all the Ruby code in there will be parsed, compiled and committed to the image, so subsequent VMs don’t have to reload all of the Ruby core when they start up. Whenever you change any code in there, you’ll have to run the maglev:reload_prims task again.

If everything went as it should, you can now use MagLev to run useful Ruby code. Like this:

$ maglev-ruby -e 'p MAGLEV_VERSION'

Step 4: Great rejoicing

That’s it, you have a basic development environment. You can now pick a feature or try and fix an issue. If you don’t know where the problem is, look around the code and get a feel for what goes where.

Further Topics

Looking at code with Topaz

If you look through the Ruby code in src/kernel, you will find class-level calls to primitive. These bind Ruby method names to Smalltalk methods. These Smalltalk methods are often found under either the src/smalltalk or src/packages directories, but they may also be just in the image. To look at what’s currently available in the image, you can use Gemtools (see above), or topaz, which ships with GemStone/S.

Provided your environment variables are set, and you are in your maglev checkout, run this:

$ bin/maglev startnetldi
$ gemstone/bin/topaz
topaz> set user DataCurator password swordfish gemstone maglev
topaz> login
successful login
topaz 1>

This logged you into the stone “maglev” as DataCurator (the default user).

topaz 1> look Module >> rubyName

category: '*maglev-runtime'
method: Module
  ^ name

topaz 1>

You’ve just looked at the method rubyName in the class module, as it is currently loaded in the stone (useful for comparing what’s in your files and what’s in the stone).

topaz 1> set class Object
topaz 1> rubylook meth inspect
method: Object
    <bridge method, objId 188217345>
method: Object
  def inspect
    # sender of _inspect must be in env 1
# method starts at line 324 of /home/tim/Devel/maglev/src/kernel/bootstrap/Object.rb
topaz 1>

And here you looked at the Ruby implementation of Object#inspect. Notice how the stone sees a method inspect#0*& - this encodes the information how many arguments a method takes.

topaz 1> rubylook meth class
method: Object
    <bridge method, objId 188189697>
method: Object
"return first non-virtual non-singleton class at or above receiver's class.

 The old method  Object>>_class is not implemented in extent0.ruby.dbf
<primitive: 730>
^ self _primitiveFailed: #class
topaz 1>

This is how a primitive looks in the stone. You have a bridge method like for a pure Ruby method, but as implementation, the stone has the Smalltalk method class (which is VM primitive 730).

Topaz has many more features, you can run and edit code. Type help and/or refer to the GemStone/S Programming Guide to learn more. This will also be useful when debugging.