[phobos] Returning Scoped Allocators From Functions

[David Simcha]

I already solved it, actually, with an extra check on destroying a region.
If the last copy of an old RegionAllocator instance dies before the last
copy of a new RegionAllocator instance, an exception gets thrown on the
death of the RegionAllocator instance and subsequent d'tor call.

On Mon, Jul 18, 2011 at 11:10 AM, Steve Schveighoffer
<schveiguy at yahoo.com>wrote:

>
> >________________________________
> >From: David Simcha <dsimcha at gmail.com>
> >
> >I'm working on retrofitting TempAlloc (renamed to RegionAllocator)to fit
> Andrei's proposed allocator interface.  One issue I've run into is, what
> happens when a scoped allocator is returned from a function?  For example:
> >
> >RegionAllocator fun() {
> >    RegionAllocator alloc;
> >    alloc.malloc(42);
> >
> >    RegionAllocator alloc2;
> >    alloc2.malloc(42);
> >    return alloc2;
> >}
> >
> >Now, alloc has died and alloc2 is still alive, violating LIFO
> requirements.  Since it's virtually impossible to do by mistake, I'm
> inclined to just make returning a RegionAllocator from a function after
> another one has been subsequently created undefined behavior.
>
> Can RegionAllocator check on postblit (called during return? not sure) at
> least in debug mode whether it's valid or not.  I think this might solve the
> problem.
>
> -Steve
>
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