CGAL users discussion list

["Thomas Zangl - Home" <>]

Am Thu, 26 Jun 2008 21:21:42 +0200, schrieb "Sylvain Pion" 
<>:

Hi!

>What kernel do you use, Exact_pred_exact_constructions it seems ?

True :-) With GMP enabled.

>This one would also have some thread-safety issues, e.g. copying
>points between threads...  Even the default constructed Point (or other
>objects from this kernel) has a shared ref-counter...

I already suspected something in this area. 
Just a short side-note:
I was reading your papers on arithmetic filtering a few days ago (for my
diploma thesis). I hope I got the big picture right, CGAL uses with
the Exact_pred_exact_constr. kernel a chain of filters (for the
predicates): Static -> Interval arithmetic -> Exact arithmetic. Is
that true? 

>I would be interested in knowing more details about your needs in this area.

We basically require that READONLY sharing of CGAL data structures is
threadsafe. In our case we do the following:

-> Create a regular triangulation and label the facets of this reg.tr.
according to some criterias. Each reg.tr. facet ist now UNIQUELY
labeled (in paractice, it got an ID). 

-> For each used label, spawn a thread and feed the reg.tr. facet
handels with the same label into the thread class' constructor. 

-> The thread does now the following:
   -> at each reg.tr. facet is an info() object with some custom
properties. One property is of a point_3 type. 
   -> Create a Delaunay_Triangulation_3 
   -> Iterate over all reg.tr . facets and insert this point_3 property
      into the Delaunay Triangulation.
   -> Create the Voronoi Diagram of the Delaunay Triang. and output it
      (write to file) 

So, we require:

-> Share a reg.tr. between the threads where we only do some read only
operations (like quering point locations or requesting the exact
coordinates of a vertex, iterating over the reg.tr., etc.) 
-> Having geometric primitives threadsafe (predicates, constructions)
-> Having a Delaunay / Regular Triang. instance for each thread and
modifying it in any way (insert, remove, iterating, .dual(), etc.). 

Thank you!

Best regards,
-- 
,yours Thomas Zangl, Bakk.rer.soc.oec. - 

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