CGAL users discussion list

[Marc Glisse <>]

On Fri, 16 Jul 2010, 

 wrote:

> Do you have any news on this ? I'm having the same issue with multithreading
> and the Simple_cartesian<Gmpq> kernel. Do you plan to fix it someday ?

It is an old thread, you could give some context ;-)

It is not possible to make reference-counting thread-safe without slowing 
down single-threaded applications, so this hasn't been done yet. It is 
safe to use different Gmpq in different threads (as opposed to Gmpzf which 
may only be used in a single thread), but not to share one between 
threads.

I am assuming that you need an exact construction kernel, or you wouldn't 
be using this one.

You could try to use a type that does not use reference counting 
(mpq_class (from gmpxx.h) instead of Gmpq).

You could also make copies of all the objects that may be accessed (even 
read-only) by several threads, before starting the extra threads, and make 
sure each thread uses a different copy.

Or you could try making Gmpq thread-safer (there used to be a prototype 
there:
http://www.loria.fr/~glisse/tmp/atomic_counter/
but it probably doesn't even compile anymore)

Good luck,

--
Marc Glisse