Re: [boost] portable precise garbage collector for C++

From: Larry Evans (cppljevans_at_[hidden])
Date: 2007-09-22 12:34:26

On 09/22/07 08:00, Achilleas Margaritis wrote:
> O/H Sebastian Redl έγραψε:
[snip]
>>
>> Then first you need the node allocator:
>>
>> typedef typename Alloc::template rebind<node<T> >::other node_allocator;
>>
>> Then you can get the new allocator's pointer type:
>>
>> typedef typename node_allocator::pointer node_ptr;
>>
>> class node
>> {
>>   T elem;
>>   node_ptr next;
>>   node_ptr prev;
>> };
>>
>> Don't forget to construct the node_allocator member you'll hold from the
>> allocator you're passed in. All allocators must have a templated
>> constructor for this purpose.
>> Something most implementations do, by the way, is that they are written
>> in such a way that EBO applies to the allocator if it has no state.
>>
> 
> But STL containers do not use the rebind struct for their internal 
> allocations or for their member pointers. They just use T* instead of 
> allocator<T>::rebind<U>::pointer.

The main_stl.zip in boost-vault/memory uses Sebastian's suggestion and
it seems to work.  It runs a little std_list test, then a GCBench
with std:pair, then GCBench with std_list<., gc_allocator>.

As (I think) you're pointing out above, the std_list<T,gc_allocator<T> >
would define gc_allocator<T>::pointer as gc_ptr<T>, which is
never used in std_list at all because the std_list stores the
complete T (not T*) in std_list<...>::node.  I can see where this
would be confusing and is a shortcoming of the allocator model.
It just happens to work in this case.