Well, there is no formal specification��� But I could summarize the features as follows (and as Christophe points mostly out)

OzVM supports having two images in logically separated spaces. This separation is achieved by using the free bit in the object header. Thus we support only two spaces by now.

- The main addition is actually a new primitive: #resumeFromSpecialObjectsArray that receives an special objects array as argument and:
    - resumes the execution from the active process of such array
    - on context switch, if the VM is running from a second special objects array, it will return to the first one instead.

- fixes to primitives/bytecodes that assume a single special objects array. e.g.,
   - #someObject and #nextObject should only iterate objects from the correct ���space���
   - #isNil comparisons should take the correct nil
   - the GC should set the correct nil object on Weak containers

The extensions I made are about 20 overrides to StackPrimitive and NewObjectMemory methods.

The rest is implemented completely on image side. We use mirror primitives to manipulate objects from other space (as each image/space has it���s own selector table).

I have in my long TODO list see if the "clever hack��� I did can be supported in a nice manner on top of Spur���s segmented memory. However, I should stop commencing new projects and start finishing them :P.

On 20 ene 2016, at 9:03 a.m., Christophe Demarey <Christophe.Demarey@inria.fr> wrote:

Hi Eliot,

Le 19 janv. 2016 �� 19:29, Eliot Miranda a ��crit :

Hi All,

    great news!  Where can I read a specification of the Oz VM facilities?

I do not know all the details of the Oz VM but basically, it is a standard stack interpreter vm specialized to be able to run 2 images at the same time on top of it. 
Guillermo made it possible by using one available bit in the object header of objects to mark the ownership of an object (e.g. is my object from image1 or image2?). Then, he mainly had to specialize VM primitives dealing with objects retrieval from memory. By example, he had to modify the garbage collector to set the right nil instance (yes, we have 2 images so 2 nil instances. we need to take the one of the active image) when an object is garbage collected; the primitive someObject has to return an object from the active image, etc.
There is also a way to switch execution from an image to the other just by switching the special objects array reference. 

The current implementation uses Cog  6.6.1and OzVM-GuillermoPolito.22.
I do not know if Guille has a more formal specification of the Oz VM.

If you have advices on what is the best way to handle two distinct object (memory) spaces in Spur, they will be welcomed :)

Cheers,
Christophe


_,,,^..^,,,_ (phone)

On Jan 19, 2016, at 6:29 AM, Christophe Demarey <christophe.demarey@inria.fr> wrote:

Hi all,

In case you do not know, we work on bootstrapping Pharo, i.e. create a Pharo image from sources, not based on a previous image (well, we use a pharo image to produce it but no code / state from it).

This process will allow to define a minimal Pharo kernel (currently 52 packages but we could have it far smaller) and to modularize the whole image (currently packages have too much dependencies on packages already loaded into the image).
The bootstrap process also allows to write down the recipe to initialize a new image from scratch (some code is missing in the image or is wrong). In addition, I think we will clean a lot of historical objects that are not used anymore.

With the amazing work done by Guillermo Polito during his Phd (around Espell, Oz): https://guillep.github.io/files/publications/Poli15Thesis.pdf, we succeeded to get a first prototype of a bootstraped Pharo 5 image (from 5.392).
This prototype is able to run an eval command line handler and to log output / errors. Not all classes are yet initialized and you cannot yet save / restart this image but it is a big step forward.
It is a 4 mb image (could be half the size without unicode data). You can download it at: http://chercheurs.lille.inria.fr/~demarey/pmwiki/pub/pharo-bootstrap/pharo-bootstrap.zip.

Next steps are to have a bootstrapped image fully working, then to load packages on top of it (like network, sunit) to produce a minimal image.
Then, we need to implement an Oz VM on top of Spur.
After that, we need to work on a reliable way to build the bootstrap (not too sensitive to changes in the image).

Christophe.

-------
demarey@193-51-236-143:~/dev/rmod/bootstrap/bootstrap-2016-01-19$ ../pharo bootstrap.image --no-default-preferences eval "1 + 1"
2
demarey@193-51-236-143:~/dev/rmod/bootstrap/bootstrap-2016-01-19$ ../pharo bootstrap.image --no-default-preferences eval "'a' , 'b'"
'ab'
demarey@193-51-236-143:~/dev/rmod/bootstrap/bootstrap-2016-01-19$ ../pharo bootstrap.image --no-default-preferences eval "1 / 0"
ZeroDivide
SmallInteger>>/
UndefinedObject>>DoIt
OpalCompiler>>evaluate
OpalCompiler(AbstractCompiler)>>evaluate:
SmalltalkImage>>evaluate:

EvaluateCommandLineHandler>>no (source is Undeclared) 
no source in EvaluateCommandLineHandler>>evaluate: in Block: no source
BlockClosure>>on:do:
EvaluateCommandLineHandler>>evaluate:
EvaluateCommandLineHandler>>evaluateArguments
EvaluateCommandLineHandler>>activate
EvaluateCommandLineHandler class(CommandLineHandler class)>>activateWith:

BasicCommandLineHandler>>no (source is Undeclared) 
no source in PharoCommandLineHandler(BasicCommandLineHandler)>>activateSubCommand: in Block: no source
BlockClosure>>on:do:
PharoCommandLineHandler(BasicCommandLineHandler)>>activateSubCommand:
PharoCommandLineHandler(BasicCommandLineHandler)>>handleSubcommand
PharoCommandLineHandler(BasicCommandLineHandler)>>handleArgument:

BasicCommandLineHandler>>no (source is Undeclared) 
no source in PharoCommandLineHandler(BasicCommandLineHandler)>>activate in Block: no source
BlockClosure>>on:do:
PharoCommandLineHandler(BasicCommandLineHandler)>>activate
PharoCommandLineHandler>>activate
PharoCommandLineHandler class(CommandLineHandler class)>>activateWith:

PharoCommandLineHandler class>>no (source is Undeclared) 
no source in PharoCommandLineHandler class>>activateWith: in Block: no source
NonInteractiveUIManager(UIManager)>>defer:
PharoCommandLineHandler class>>activateWith:
no source in BasicCommandLineHandler>>activateSubCommand: in Block: no source
BlockClosure>>on:do:
BasicCommandLineHandler>>activateSubCommand:
BasicCommandLineHandler>>handleSubcommand
BasicCommandLineHandler>>handleArgument:
no source in BasicCommandLineHandler>>activate in Block: no source

SmallInteger>>no (source is Undeclared) 

UndefinedObject>>no (source is Undeclared) 

AbstractCompiler>>no (source is Undeclared) 

SmalltalkImage>>no (source is Undeclared) 

BlockClosure>>no (source is Undeclared) 

EvaluateCommandLineHandler>>no (source is Undeclared) 

EvaluateCommandLineHandler>>no (source is Undeclared) 

CommandLineHandler class>>no (source is Undeclared) 

BasicCommandLineHandler>>no (source is Undeclared) 

BasicCommandLineHandler>>no (source is Undeclared) 

PharoCommandLineHandler>>no (source is Undeclared) 

UIManager>>no (source is Undeclared) 

UndefinedObject>>no (source is Undeclared) 

CommandLineUIManager>>no (source is Undeclared) 

SmalltalkImage>>no (source is Undeclared) 

DelayMicrosecondScheduler>>no (source is Undeclared) 

BlockClosure>>no (source is Undeclared) 

SmalltalkImage>>no (source is Undeclared) 

WeakArray class>>no (source is Undeclared) 


ps: source cannot be displayed because there is no formatter available in the bootstrap