[vtk-developers] Proposal: Simplify vtkDebugLeaks registration

David Lonie david.lonie at kitware.com
Thu Sep 8 17:42:21 EDT 2016

Hi all,

We've been seeing some issues surrounding the use of vtkDebugLeaks and
template classes lately. The main problem stems from the difficulties
of ensuring that ::GetClassName() returns a unique string for
different instantiations of a templated object. This is important to
ensure that things like SafeDownCast work correctly.

At the moment, ::GetClassName() returns typeid(this).name() for
templated types, which is typically very different from the string
passed into vtkObjectFactory::ConstructInstance(...) by the object
factory macros used to implement the ::New() methods.

Right now we jump through some hoops to try to make sure that
vtkDebugLeaks::ConstructClass is called with the ::GetClassName()
string, since that is used when vtkObjectBase::UnregisterInternal
removes an object from the leak tracker. But we've missed some spots
and there are quite a few classes that don't bother with the macros,
and thus have custom implementations of ::New() that need to
explicitly register themselves with DebugLeaks. It's getting messy and
problematic trying to keep all of this consistent.

I propose that we simplify DebugLeaks to make the registration happen
automatically. I see a couple of ways to do this:

1) Just track the objects directly by registering their addresses in
vtkObjectBase's constructor. This would increase the memory footprint
of vtkDebugLeaks, but I think that's not a huge issue since
vtkDebugLeaks is a testing/development tool that isn't used in
production AFAIK. This would also allow a more detailed printout of
the leaked objects since we could call Print() on them.

2) Continue registering name strings, but do so from a
vtkObjectBase::InternalInitialize() (or similar) method that calls
vtkDebugLeaks::ConstructClass(this->GetClassName(). This would still
need to be called explicitly in custom ::New() implementations, but it
would be easier to maintain, update, and keep consistent/correct
thanks to the encapsulation to a single method.

Note that we can't just call
vtkDebugLeaks::ConstructClass(this->GetClassName()) from
vtkObjectBase's constructor due to how virtual methods in constructors
work. ::GetClassName() will always return "vtkObjectBase" when called
from vtkObjectBase's constructor.

Any thoughts/objections/suggestions?


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