[Insight-developers] Circular smart pointer references causing memory leaks

[Bill Lorensen]

I vote for "don't do that". Seems like a design flaw.

On Thu, Aug 4, 2011 at 11:40 AM, Williams, Norman K <
norman-k-williams at uiowa.edu> wrote:

> Vince figured this out and solved one leak, but it points to something
> that I didn't think about that needs to be guarded against.
>
>
> class A contains a SmartPointer to instance of class B
> class B contains a SmartPointer to instance of class A
>
> Whoever wrote A & B thought that the destructors of instances of A & B
> would in turn call the destructors for the smart pointers, and eventually,
> the instances of A & B would all be freed when no smart pointers to them
> went out of scope.
>
> But this isn't the case and here's why: Even after all third party
> SmartPointers to A & B go out of scope, the instances of A & B will still
> have a reference count of 1, so the destructors will never get called, and
> the smart pointer members will live forever.
>
> The only solution, apparently, is that there needs to be a Pre-destructor
> that clears all smart pointers in the class, that gets called before all
> the smart pointers to an object go out of scope or get re-assigned.
>
> Now, in general, this isn't a problem, but the FEM code is a multiple
> interconnected cyclic graphs of smart pointer references. Knowing that I
> can begin to try and fix it.
>
> But it points up a weakness in ITK's dependence on Smart Pointers.  Even
> though in most cases, it solves memory allocation issues; in others it's a
> nightmare, where letting a SmartPointer to an object go out of scope
> actually makes the object pointed to immortal.
>
> Anyone have any ideas how to fix this other than "don't do that!"?
>
>
>
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