[vtk-developers] RELEASE_DATA doesn't?

[Wilson, Andrew T]

Summary: the vtkDemandDrivenPipeline::RELEASE_DATA() key is always removed the first time a pipeline executes.

I'm working on a pipeline that needs to use RELEASE_DATA almost everywhere.  If I use vtkDataObject::SetGlobalReleaseDataFlag() then ReleaseData() gets called.  If I use vtkAlgorithm::SetReleaseDataFlag then ReleaseData() never gets called.

I've tracked this down to the following chain of events during pipeline execution:
  - vtkDemandDrivenPipeline::ExecuteDataObject calls CheckDataObject to make sure the output object is there.
  - CheckDataObject notices that there is no data object yet, creates one, and calls vtkExecutive::SetOutputData().
  - SetOutputData puts in place the new output object and calls ResetPipelineInformation().
  - vtkDemandDrivenPipeline::ResetPipelineInformation removes the RELEASE_DATA key.

The net result is that calls to SetReleaseDataFlag() before the pipeline is executed will have no effect.  This seems like a bug.  I have a couple of ideas regarding how to fix it but since this is at the heart of the pipeline I'd like input from pipeline hackers first.

Idea #1: Don't call ResetPipelineInformation() from SetOutputData().  If a filter wants to reset the pipeline keys make it do so itself.

Idea #2: Only call ResetPipelineInformation() if SetOutputData() is replacing an existing object.

Thoughts?

-- Andy

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