Re: boost::singleton_pool<...>::release_memory problem

 Barry <>
Tue, 10 Jul 2007 08:09:09 -0700
On 7 10 , 8 44 , dasjotre <> wrote:

On 10 Jul, 03:37, Barry <> wrote:

As boost::pool_alloc use singleton holder for pool allocator, client
programmers have to reclaim the memory by hand through calling
singleton_pool<alloc_tag, elem_size>::purge_memory() or something to
release the memory, so the program should have knowledge of the
elem_size, sometime, it's impossible or at least hard to know the size
of the element allocated by the allocator.
for example:
struct my_tag
list<int, boost::pool_allocator<int> > List;

Here _List_node is the real element that is dynamic created by
allocator, so if I use sizeof(int) instead, it does NOT work

indeed, list uses rebind mechanism to define allocator to use.
_List_node is implementation detail and you should not use it.

I don't think there is a way to achieve that other than to extend

something like
template <class T, ...>
class my_pool_allocator : public boost::pool_allocator<T, ...>
.. forward constructors here

// rebind
        template <typename U>
        struct rebind
                typedef my_pool_allocator<U, ...> other;

        bool release_memory() const
                return ::boost::singleton_pool
                        < ::boost::pool_allocator_tag
                        , sizeof(T)


std::list<int, my_pool_allocator<int, ...> > list;



As check out SGI and Dimkumware STL implementation, I found that they
neither rebind the XX_node(something like that) to be their
allocator_type, they separately provide _Buynod and _M_get_node to
create a node,

So the following code below in MSVC 8.0:

template <class T>
struct my_pool_allocator : pool_allocator<T> {
    my_pool_allocator() : pool_allocator<T>() {}
    my_pool_allocator(my_pool_allocator<T> const&) : pool_allocator<T>()
    my_pool_allocator(pool_allocator<T> const&) {}

    template <class U>
    struct rebind {
        typedef my_pool_allocator<U> other;

    static bool release_memory()
        return singleton_pool
            < pool_allocator_tag
            , sizeof(T)



int main(int argc, char* argv[])
    typedef list<int, my_pool_allocator<int> > mylist;
    mylist IntList;
    cout << typeid(IntList.get_allocator()).name() << endl;
    return 0;

produces the result:
struct my_pool_allocator<int>
and it really does not reclaim memory as I walk into the function

I don't konw the my_pool_allocator extension is right or not, but I
think it does not affect the result

So, if the container is not vector, it's hard to use
boost::pool_allocator and release_memory, if not hopeless


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