Re: [boost] Re: Boost memory management guidelines

From: E. Gladyshev (egladysh_at_[hidden])
Date: 2003-09-02 16:52:18

--- Gregory Colvin <gregory.colvin_at_[hidden]> wrote:
[...]

> > 3. If your class is using STL containers, use boost::memory::allocator
> >    adapter (see bellow).
> 
> Why not just use std::allocator?

Because boost::memory::allocator will use UserAllocator under the covers.
So if you customized UserAllocator parameter, you customized 
how STL allocate their memory as well.

> 
> > 4. To construct/destroy objects, use boost::memory::construct/destroy.
> 
> See below.
> 
> > 5. Avoid using explicit references to allocators.
> >
> > ... Usage example:
> > ==============
> > template< typename T, typename UserAllocator = 
> > boost::default_user_allocator_new_delete >
> > class X
> > {
> 
> What if you want X to use the same allocator as some other STL container
> constructed with a non-Boost allocator?  That would be difficult unless
> you have [...]

Yes.

> >     T* _p;
> 
> How to pass arguments to T's constructor?  Better just
> 
>    p = new(UserAllocator::malloc(sizeof T)) T(...)
> 
> >     }
> >     ~X()
> >     {
> >         if( _p )
> >             boost::memory::destroy<T, UserAllocator>( _p, 1 );
> 
> In which case, why not just
> 
>    p->~T(), UserAllocator::free(p);
> 
> ?

The boost::memory::construct/destroy are just convinience wrappers
that will do like just that.
They can also handle exceptions properly.

struct memory
{

template< typename T, typename A >
static void destroy( T* p )
{
  try
  {
    p->~T();
    A::free(p);
  }
  catch( ... )
  { 
    A::free(p);  //free memory even if the destructor crashes.
    throw;
  }
}

};

Eugene

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