[Ironpython-users] LightweightScopes and scopes in general

[Igor Brejc]

On Fri, Feb 10, 2012 at 7:46 PM, Dino Viehland <dinov at microsoft.com> wrote:

>
>
> Jeff wrote:
> > I'm taking a stab off the top of my head based on my limited knowledge
> of the
> > internals, but I do know that debug code is not collectable.
> > It's possible that the code itself may be holding references that keep
> objects
> > alive longer than expected.
> >
> > I believe if you run the code in a separate AppDomain you can unload the
> > AppDomain and the code will be collected, which should take everything
> else
> > with it.
> >
> > >
> > > I've also tried running in the release mode and turning on the
> > > options["LightweightScopes"] = true mode, which seems to help. But I
> > > cannot find any information about what this option actually does and
> > > what happens with the scope variables in general. Any info would be
> > appreciated.
> >
> > That one I'll have to leave to Dino.
>
> The difference between the different types of scopes just comes down to how
> we hold onto global variable and call site objects.
>
> The most efficient way to hold onto these is to use CLR static fields to
> store the
> global variables.  That allows the CLR to generate a direct access to the
> field and
> we can quickly access the global variables.  But it comes at the cost of
> not being
> able to recover the static fields and leaking the values that are stored
> in there.
>
> The light weight scopes store the variables in a field or an array instead
> of storing
> them in static fields.  To do that we need to pass in the field or close
> over it and then
> on each access we need to do the field or array access (and if it's an
> array access, it
> needs to be bounds checked).  But the end result is that the only thing
> which is keeping
> the global variable / call site objects alive are the delegate which
> implements the
> ScriptCode.  Once the ScriptCode goes away all of those call sites and
> PythonGlobal
> objects can be collected.
>
> So lightweight scopes come at a performance cost, but they are more
> applicable
> Where you're actually re-compiling code regularly.
>
>
>
Thanks for that explanation, Dino.

Another question that pops up: what happens with Disposable objects (like
files, GDI+ bitmaps etc.) created within the Py scope (if they are not
referenced from the outside)?

Igor
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/ironpython-users/attachments/20120210/a34369ac/attachment.html>