Processes in GNU Smalltalk

Hi,

GNU Smalltalk and I guess most of the Smalltalk implementations,
only provide green threads, that means we have a share everything
approach with the others threads. We clearly lacks of a process
isolation model in Smalltalk, I propose a model to have them with
a relative small cost. Since a process share nothing with the other
processes, we need to generate for each processes  a set of base
classes and objects (Object, Class, Array, ... with their compiled
methods, a symbol table).

Separation has multiple advantages:
  - security
  - sandboxing
  - concurrency
  - resource management
  - ...

A simple and nice approach to have them in GNU Smalltalk is to add
a support for multiple SpecialObjectArray. SpecialObjectArray is a
special object used for storing all the objects that the virtual machine
knows for instance: true, false, nil, #doesNotUnderstand, the list of
processes, ...

GST doesn't have a special object array in the VM because it has an
object table and thus some objects positions are hard-coded, adding
a special object array could also help us for the OT removal ;-)

A new Domain class should be added it's the real process (and not
thread) and the Process (the thread :D) class is extended with a new
domain instance variable. The Domain class stores the special object
array and thus each time the scheduler chooses another thread it has the
process and can swap the special object array.

Cheers,
Gwen

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