[vtkusers] ReleaseDataFlag

[Tim Hutton]

Hello VTK people,

I'm confused about the ReleaseDataFlag. A couple of my own filters were 
using a lot of memory, so I called 
vtkDataObject::SetGlobalReleaseDataFlag(1) to try to release memory from 
earlier in the pipeline that was no longer needed. This works spectacularly 
for one of them, everything was fine. For the other, however, I got 
problems because towards the end of the Execute() function the data in 
this->GetInput() had been released and had gone! I think the problem is 
captured in this sketch:

void MyFilter::Execute()
{
   ...

   this->GetInput()->GetCell(id); // fine, since data not released

   ...

   vtkTransformPolyDataFilter trans
      trans->SetInput(this->GetInput());
      ...
      trans->Update();

   ... // use output of trans

   this->GetInput()->GetCell(id); // ERROR! data has been released!

}

When trans has finished, it checks to see if it can release its data. The 
global flag says yes, so it releases this->GetInput() which is disastrous.

How do I stop the data being released mid-Execute? Using 
ReleaseDataFlagOff() calls doesn't work because the global flag overrides 
them! (see vtkDataObject::ShouldIReleaseData)

I'm using the latest CVS of VTK4 on win2k with visualc++6.

Thanks,

Tim.
---------------------------------------------------------------------------
Tim Hutton,                        http://www.eastman.ucl.ac.uk/~dmi/MINORI
Research Fellow & PhD student,                   T.Hutton at eastman.ucl.ac.uk
MINORI Project, Biomedical Informatics Unit,     Tel: [+44] (0)20 7915 2344
Eastman Dental Institute, UCL,                   Fax: [+44] (0)20 7915 2303
256 Gray's Inn Road, London WC1X 8LD, UK      Mobile: [+44] (0)7748 678 832
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