[Ironpython-users] LightweightScopes and scopes in general

[Igor Brejc]

I'm thinking of this scenario: my host application allows users to run
their own Py scripts. OK, in the ideal case, their scripts should take care
of the disposal of the reserved resources, but a lot of times user will
write trail-and-error scripts which will often fail. Is there a mechanism
for the host application to somehow track (and possibly dispose) of the
stuff that has been allocated in a failed user script? Using SetTrace() or
by simply examining the ScriptScope after the script has finished? Or
should I simply ignore this?

I'm wondering how other people who use IronPython as an embedded scripting
engine deal with these issues (if at all).

Thanks,
Igor

On Fri, Feb 10, 2012 at 10:40 PM, Dino Viehland <dinov at microsoft.com> wrote:

>  We won’t call IDispose on them.  Usually they’ll follow the pattern of
> implementing IDisposable + having a finalizer so they will eventually
> release their resources.  Also they can be used with the “with” statement
> so that their Dispose methods are eagerly called.****
>
> ** **
>
> *From:* Igor Brejc [mailto:igor.brejc at gmail.com]
> *Sent:* Friday, February 10, 2012 10:51 AM
> *To:* Dino Viehland
> *Cc:* Jeff Hardy; Ironpython-users at python.org
> *Subject:* Re: [Ironpython-users] LightweightScopes and scopes in general*
> ***
>
> ** **
>
> ** **
>
> 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****
>
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