On Tue, May 22, 2012 at 03:24:34PM -0700, Eliot Miranda wrote:
> On Tue, May 22, 2012 at 12:07 AM, Colin Putney <colin at wiresong.com> wrote:
> 
> > Hi all,
> >
> > I've just uploaded a package to the Inbox for review by the community:
> >
> > http://source.squeak.org/inbox/Mirrors-cwp.2.mcz
> >
> > It's a simple first step at creating a mirror API for Squeak. I've only
> > implemented ObjectMirror and ObjectVmMirror, which provide high- and
> > low-level reflection on an object. This implementation has a twist,
> > however: it sends no messages to the object it's reflecting. That allows us
> > to reflect on network proxies, ORM stubs, mock objects and the like without
> > triggering any state changes.
> >
> > As a proof of the concept, I've implemented a rudimentary non-invasive
> > MirrorInspector. The main thing that's missing is non-invasive printing,
> > which would take a bit of work to implement, but isn't necessary for a
> > demo. To see it in action do try the following in a workspace.
> >
> > WARNING: Read the comments carefully, and don't do this in an image you
> > care about!
> >
> > "This creates a very dangerous object"
> > Object subclass: #Nuke
> > instanceVariableNames: 'one two three'
> > classVariableNames: ''
> > poolDictionaries: ''
> > category: 'Test'.
> > class := Smalltalk at: #Nuke.
> > class superclass: nil.
> > inst := class basicNew.
> >
> > "This is harmless"
> > MirrorInspector inspect: inst.
> >
> > "This will crash your image"
> > inst yourself.
> >
> > The implementation uses primitive 188 to directly execute CompiledMethods
> > with the reflected object as the receiver, thus giving us access to the
> > object's state without sending it a message.
> >
> 
> In part you can use the light-weigth mirror methods in ContextPart, these
> take the object operated on as an argument.  Non-invasive printing could be
> done via execution simulation.  I've already modified the Squeak debugger
> in Qwaq/Teleplace images to use these light-weight mirror primitives so
> that messages are not sent to receivers when simulating execution in the
> debugger (i.e. when doing send instead of step).  If the mirror primitives
> now work on the interpreter I can fold this into trunk.  David, do the
> mirror primitive tests pass on the interpreter?

All mirror primitive tests pass on the interpreter VM if built with the
latest VMMaker and SVN sources. However, the mirror primitive support is
not yet present in any officially released standard VM.

The updates for mirror primitive support were added in VMMaker-dtl.262 and
VMMaker-dtl.261. Note the update comment in VMMaker-dtl.262, as the
implementation differs from Cog and a code review would be welcome:

    Name: VMMaker-dtl.262
    Author: dtl
    Time: 5 January 2012, 12:41:29.745 am
    
    VMMaker 4.7.19
    
    Reference Mantis 7429: Add Mirror Primitives to the VM
    
    Update primitivePerformInSuperclass to support ContextPart>>object:perform:withArguments:inClass:
    
    Implementation differs from that of oscog in that the original primitivePerformAt:
    is retained unmodified, and the necessary stack adjustments are done in
    primitivePerformInSuperclass for the special case of argumentCount 4
    (mirror primitive call) rather than 3. The oscog approach may be prefered
    (not least for its clearer method naming), but making the change in
    primitivePerformInSuperclass is low risk and more easily implemented by
    a Sunday Squeaker.
    
    All MirrorPrimitiveTests pass.

Dave