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Re: [Gnash-dev] GC and refcount
From: |
strk |
Subject: |
Re: [Gnash-dev] GC and refcount |
Date: |
Tue, 22 Dec 2009 20:31:49 +0100 |
A posible solution to this problem is having
intrusive_ptr_add_ref(const ref_counted* o)
and
intrusive_ptr_release(const ref_counted* o)
NEVER dereference 'o' but rather ask the GC
to manage the reference count. The GC might
keep a map of managed resources and do
nothing if they are no more in the list.
Only thing to take care of in this case would
be ensuring that the objects-to-be-deleted won't
be really deleted (freed) until the intrusive_ptr
they contain are reset, which means adding a method
to every objects who may contain references to
GcResources to use for 'clearing' all those references
before destruction.
--strk;
On Mon, Dec 21, 2009 at 06:49:55PM +0100, strk wrote:
> Ehm.... for the record, the case to think about is the unreachable
> chain of GcResources circularly referencing each-other trouh this
> "smart pointer".
> The GC would delete the resources, so the "smart pointers" would
> NOT be able to access the actual referee object w/out memory violations.
>
> We'd then need a way from the GC to signal all smart pointers about
> this condition. Chances are weak pointers would help here, but I've no
> experience with that (will do some research).
>
> --strk;
>
> On Mon, Dec 21, 2009 at 06:32:12PM +0100, strk wrote:
> > I've created a new shared branch for the GC work:
> > bzr branch http://bzr.savannah.gnu.org/r/gnash/branches/gc
> >
> > The GC version in the branch allows "manual" deletion of GcResource
> > objects by having GcResource destructor remove self from the GC-managed
> > list. Cost of this is + sizeof(std::list::iterator) per GcResource.
> > Removal from the std::list runs in constant time.
> >
> > Now that we have that possibility, adding a ref-count in GcResource
> > would let us remove earlier any object not containing circular refs.
> > Only trouble would be making sure intrusive_ptrs for GcResource
> > are properly used within the whole codebase.
> > The SafeStack implementation would need to stop keeping as_value
> > alive in order for memory reduction to be noticeable.
> >
> > --strk;
> >
> >
> > On Sat, Dec 19, 2009 at 12:17:43PM +0100, strk wrote:
> > > Here's another idea to reduce memory use.
> > > We could mix refcount and gc for the GcResources
> > > so that in absence of circular refs we'll release
> > > them sooner.
> > >
> > > The additional overhead would be:
> > > - refcount management (per reference)
> > > - GC list management (per object)
> > >
> > > Implementation:
> > > - manage GcResources with intrusive_ptr<>
> > > like others.
> > > - Tweak add/drop refs for GcResource in libbase/smart_ptr.h
> > > - Tweak GcResource to add refcount and signal GC
> > > about being removed.
> > >
> > > --strk;
> > >
> > > Free GIS & Flash consultant/developer () ASCII Ribbon Campaign
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> > >
> > >
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> >
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