[vtk-developers] vtkAbstractTransform and thread safety

[David Lonie]

Hi David,

I noticed in the vtkAbstractTransform class that there are a set of mutexes
that guard the Update() and GetInverse() methods. Are these necessary? They
were introduced in this commit:

commit 793c003c5064ff90bfee3769d6b85cc4c75104f6
Author: David Gobbi <david.gobbi at gmail.com>
Date:   Wed May 3 16:53:37 2000 -0400

    ERR: The way that GetInverse worked, there was no easy way to fix the
         existing memory leak.  So the GetInverse mechanism has changed (and
         is more efficient than it used to be) but significant other changes
         were necessary.


I'm looking at the performance of some filters, and vtkGlyph3D makes heavy
use of the transform classes to position/scale the glyphs before copying
them into the output. Trouble is, each new transform dynamically allocates
two mutexes, and building up the transforms requires entering critical
sections. Benchmarking Glyph3D shows that removing these mutexes cuts out
about 10% off of the time it takes the filter to update. I imagine this
overhead is hurting performance in other instances, too.

Since VTK isn't typically thread-safe and most uses of the transforms (that
I'm aware of) are single-threaded, it seems reasonable to me that these
should be removed. Is there any reason to keep them?

Thanks,
Dave
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