[Insight-developers] Introducing itk::AutoPointer

[Luis Ibanez]

Hi,

As you may recall, the Cell classes were recently
modified to not derive from the itkLightObject.

This change allowed to avoid the time overhead of
Mutex calls during Register() and Unregister()
operations.

The change, however difficulted some of the operations
required in the itkMesh and itkCells class.

In particular:

itkCells are capable of returning their boundaries,
for example a triangle cell is capable of returning
the three line cells which are its boundaries.

The line cells are not actually stored but rather
constructed on the fly upon demand. This creates a
confusing memory managment situation, since it is
not clear who will be responsible for memory release.

At the level of the itkMesh that was solved by creating
a list which contains pointers to cells whose memory
should be released upon destruction of the Mesh.
At the level of the Cell, however it is not possible
to apply the same solution.

Given that cells are not intended to be shared,
this is not exactly a problem of reference counting.
We just want to make sure that somebody will take care
of releasing the memory allocated for the cell.

In response to this need the new class itk::AutoPointer
is being introduced.  The AutoPointer is a helper
class that holds a raw pointer. In the same way that
the itkSmartPointer the AutoPointer is designed to
look pretty much like a raw pointer.

The special feature of this new pointer type is that
upon destruction it will release the memory allocated
by its raw pointer.  That guarranties that at the
end of the scope memory leaks will be controlled.
The memory can also be released explicitly before.

There is a std::auto_ptr already. The reason for not
using this standard class is that it has templated
method that will result in difficulties during
wrapping.

Methods returning Cells from the itkMesh and itkCell
classes will return AutoPointers in order to transfer
the responsibility of memory release to the recipient
if the call.

Storage of Cells inside the itkMesh will still be done
by a VectorContainer of raw pointers to cells.


The details of the implementation and the changes
over the toolkit are being worked out.



      Luis