CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Hi Bernhard,

thanks for the patch, we'll look into it soon and let the list know
about the integration status.
We'll come back directly to you if we have any question.

Best,

Sebastien.

On 01/21/2015 12:06 PM, Bernhard Kornberger wrote:
> Hello!
>
>
> Last year researches from the Distributed and Parallel Systems Group
> of the University of Innsbruck have parallelized one of my programs.
> To this end they needed to patch CGAL to achieve thread safety for
> the Exact_predicates_exact_constructions_kernel. Now I'd like to
> contribute this patch and possibly start a discussion about it:
>
> http://www.geom.at/_downloads/patch.diff
>
> The patch is not my work, so I paste their description here:
>
>
>
> ### Copy&Paste start ###
>
> The handler classes implement reference counting mechanisms. A simple
> atomic increment
> operation was added to the counter increment to avoid concurrent
> alteration. To provide portability,
> the boost::atomic tools were used, instead of using compiler dependent
> built/in functions.
> The current C++11 standard could have been used as well, std::atomic
> provides with the same functionality and portability.
> The modified files are: CGAL/Handle_for.h and CGAL/Handle.h
>
> In CGAL/Lazy.h the version of the approx() method that is not constant
> and do returns a reference to the inner
> object was dropped. We want to avoid anyone from modify the state of the
> object so we can enforce thread
> safety. It seems that this method is not used during compilation and can
> be safely deleted.
> The Lazy_rep object keeps two objects that hold the approximate value:
> at, that holds the
> original approximate value, and at_exact that holds the exact value that
> is recalculated inside
> update_exact. In this way, a thread that calls approx and ta thread that
> calls update_exact operate on
> different objects and we can ensure thread safety.
> Instead of utilizing a mutex to check whenever the approximate value has
> being updated, the
> check is done done via an atomic counter. This counter is initialized
> with value 0 to represent that
> the value is an approximation. The last statement of the update_exact
> operation updates the value to
> represent the fact that the value is no longer an approximation.
>
> ### Copy&Paste end ###
>
>
> I hope that this contribution is useful.
>
> Best regards
> Bernhard Kornberger