[boost] Re: Re: Re: Re: Proposals: p2m offsets, prebuild<>, squad_ptr<>(of course)

From: Philippe A. Bouchard (philippeb_at_[hidden])
Date: 2002-09-03 12:53:58

Larry Evans wrote:

[...]

> parent.  This leaves
> the non-zero rc pointers only on stack. These are then traced to find
> the live rc pointers.
> The rest are collected.  Hence, the time taken would be comparable to
> that taken by
> a regular conservative GC.  The only difference it the method to
> enumerate the rc pointers
> on the stack.

What about implementing some exception when get_count() == 2.  Given:
bool is_on_data(void * p); // Confirm p is address on data segment
bool is_on_stack(void * p); // Confirm p is address on stack segment
bool is_on_heap(void * p); // Confirm p is address on heap segment

struct placed_ptr_header
{
        int m_count;
        void * m_owner;  // Could point to stacked candidate for destruction
};

placed_ptr<T>::placed_ptr(...)
{
        if (is_on_stack(this))
        {
                get_owner() = this;
        }
        ...
}

placed_ptr<T>::~placed_ptr()
{
        if (m_ptr)
        {
                -- get_count();

                if (get_count() == 0)
                {
                        m_ptr->~T();
                        free(m_ptr - ...);
                }
                else if (get_count() == 1 && get_owner() == this)
                {
                        m_ptr->~T();
                        free(m_ptr - ...);
                }
        }
}

This is highly simplified and I'm not sure where this will lead to yet.

-- 
Philippe A. Bouchard