Re: [Boost-users] [Wave] effect of allocation of data structures oncopying data structures

From: Andreas Sæbjørnsen (andreas.saebjoernsen_at_[hidden])
Date: 2006-05-11 13:27:08

My scenario is number 1) here, so I have to be very careful with the memory
use. I should then probably use
the std::copy using the inserter to copy the values into a data structure
allocated using the standard
allocator. When trying to free the memory allocated by Wave when I use it as
a shared library,
is it enough to delete the variable declaration of type context_type?

Regards
Andreas

On 5/10/06, Hartmut Kaiser < hartmut.kaiser_at_[hidden]> wrote:
>
>
>
> > Andreas Sæbjørnsen wrote:
> >
> > > I need some advice regarding how I should copy the boost data
> > > structures I get from 'advanced_preprocessing_hooks.h'.
> > > The task at hand is to copy some of the data structures
> > from Wave and
> > > store it separate form the memory Wave allocates so that after the
> > > Wave preprocessing step has finished all it's memory can be freed.
> > >
> > > Example: e.g making a copy of the
> > > 'std::vector<std::list<PreprocessingInfo::token_type,boost::fa
> > > st_pool_allocator<PreprocessingInfo::token_type> > >'
> > > representing the arguments in the expansion of a macro in
> > the function
> > > 'expanding_function_like_macro'.
> > >
> > > Syntactically it would be gre at to be able to make a copy
> > using the
> > > operator=, but as far as I can see this is only possible if
> > I am also
> > > using the fast_pool_allocator. If I use the
> > fast_pool_allocator I am
> > > afraid that my copies will be put into the memory pool allocated by
> > > Wave and therefore that memory cannot be safely freed. Is
> > this corect?
> >
> > I'm not sure here. My (unverified) guess is, that the memory
> > pool will be free'd only after the last item allocated from
> > it got free'd. This shouldn't be a problem as long as the
> > memory pool doesn't live in a shared library which gets
> > unloaded prematurely.
>
> After looking at the code and the docs again I discovered the following:
> the
> boost::fast_pool_allocator is build on top of a thread local singleton
> pool.
> This pool gets allocated before entering main and gets free'd after main
> exits. Same should be true for shared libraries.
>
> So yes, you're running into problems only:
> 1) if you have your Wave application compiled into a shared library and
> 2) if you use data from the allocator used by Wave in a different module
> after the first shared library was explicitely unloaded from memory.
>
> HTH
> Regards Hartmut
>
>
> > But anyway, doesn't using std::copy() for the embedded
> > list<>'s allow to change to any adequate data structure?
> >
> > Regards Hartmut
> >
>
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