Re: [boost] [pool] Why no singleton_object_pool?

From: Jason Hise (chaos_at_[hidden])
Date: 2005-09-29 16:29:44

Joel Eidsath wrote:

>My main purposes right now are familiarizing myself with Boost.
>
> From reading the header file for aligned_storage, I believe that I 
>understand how to do what you're suggesting, although I admit that I am 
>somewhat shaky -- I'd have to figure it out by implementing it, I think.
>
>But correct me if I'm wrong: I don't think that it would be possible to 
>use purge_memory to destruct everything at once like that.  You'd have 
>to destruct everything individually.
>
I haven't personally worked with the pool allocators much, so perhaps my 
suggestion was misplaced.  I was thinking that you wanted a pool that 
allocated only enough memory for a single instance, rather than a single 
instance of a pool that could store many objects.  Anyhow, to use 
aligned_storage like I was thinking, you might do something like:

template < typename Type >
class SingletonPool
{
private:
    typename boost::aligned_storage < Type >::type mem;
    bool exists;
    Type * pmem;

public:
    SingletonPool (  )
        : exists ( false )
        , pmem ( reinterpret_cast<Type *>( &mem ) )
    {
    }

    Type * instance (  )
    {
        if ( !exists )
        {
            new ( pmem ) Type (  );
            exists = true;
        }
        return pmem;
    }

    void release (  )
    {
        if ( exists )
        {
            pmem->~Type (  );
            exists = false;
        }
    }

    ~ SingletonPool (  )
    {
        release (  );
    }
};

But this probably wasn't what you were after...

-Jason