[Dune-devel] [Dune-Commit] [Commit] dune-common - f78ce3a: [poolallocator, release] Use a non-static memory pool.

[Markus Blatt]

Hi Carsten,

On Thu, Jan 30, 2014 at 04:29:25PM +0100, Carsten Gräser wrote:
> this looks like a (potentially dangerous) interface change to me.
> Its a change since different instances of the same allocator
> type are no longer equivalent. Furthermore its dangerous
> for the following reason:
> 
> While an stl conforming allocator is in principle allowed to be
> stateful, the standard also explicitly allows that stl implementations
> may require that the allocator is stateless.
> 

Is that really the case? I tried to find this in the C++11 standard,
but to no avail. It even seems to be contrary to me, as there are
interface methods like operator==(other) for testing whether memory
allocated by one allocator might be deallocated by the other.

Seems like this was different in previous standards. But most
implementations do support them:
http://stackoverflow.com/questions/6861046/compiler-support-for-stateful-allocators-in-stl-containers

> Strictly speaking, you can no longer use the pool allocator
> with stl containers unless you know that your specific stl
> implementation supports stateful allocators.
> 

Is anybody doing that? Poolallocator only allows to allocate 1 element
at a time which rules out quite a few containers. At least in the core
modules it only used in dune-istl's AMG and that is where it makes
trouble.

> I'm not proposing to revert the patch and I'm also not sure how to
> resolve this issue. I think thats one of the reasons why the allocator
> design is said to be broken. However we should at least warn the user
> in the docs and the release notes if we keep this patch.

If we agree that stateful allocator are supported by c++11 and above
we could at least apply this behaviour for compilers which support
that.
> 
> Best,
> Carsten
> 
> Am 29.01.2014 19:51, schrieb Markus Blatt:
> > New commit, appeared at Wed Jan 29 19:51:28 2014 +0100
> > as part of the following ref changes:
> > 
> >     branch refs/heads/master    updated from 75e2716 -> f78ce3a
> > 
> > Browsable version: http://cgit.dune-project.org/repositories/dune-common/commit/?id=f78ce3a8db88ecda77664f6e7bfa480768e2e999
> > 
> > ======================================================================
> > 
> > commit f78ce3a8db88ecda77664f6e7bfa480768e2e999
> > Author: Markus Blatt <markus at dr-blatt.de>
> > Date:   Wed Jan 29 19:48:38 2014 +0100
> > 
> >     [poolallocator,release] Use a non-static memory pool.
> >     
> >     Due to its desgin of using one static memory pool. The allocator
> >     could not be used in different threads at the same time without
> >     side effects. With this revision each instance will hold its own private
> >     instance of the pool.
> >     
> >     There should be no issues with this patch and poolallocator seems to be
> >     mostly used in AMG anyway.
> > 
> >  dune/common/poolallocator.hh | 5 +----
> >  1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > 
> > 
> > diff --git a/dune/common/poolallocator.hh b/dune/common/poolallocator.hh
> > index 9bb4897..e7555bd 100644
> > --- a/dune/common/poolallocator.hh
> > +++ b/dune/common/poolallocator.hh
> > @@ -368,7 +368,7 @@ namespace Dune
> >      /**
> >       * @brief The underlying memory pool.
> >       */
> > -    static PoolType memoryPool_;
> > +    PoolType memoryPool_;
> >    };
> >  
> >    // specialization for void
> > @@ -552,9 +552,6 @@ namespace Dune
> >    }
> >  
> >    template<class T, std::size_t s>
> > -  typename PoolAllocator<T,s>::PoolType PoolAllocator<T,s>::memoryPool_;
> > -
> > -  template<class T, std::size_t s>
> >    inline PoolAllocator<T,s>::PoolAllocator()
> >    { }
> >  
> > 
> > _______________________________________________
> > Dune-Commit mailing list
> > Dune-Commit at dune-project.org
> > http://lists.dune-project.org/mailman/listinfo/dune-commit
> > 
> 
> 

-- 
Do you need more support with DUNE or HPC in general? 

Dr. Markus Blatt - HPC-Simulation-Software & Services http://www.dr-blatt.de
Hans-Bunte-Str. 8-10, 69123 Heidelberg, Germany
Tel.: +49 (0) 160 97590858  Fax: +49 (0)322 1108991658 
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