#19 Should be able to create std::shared_ptr with pool_allocator

khizmax — Wed, 04 May 2016 19:50:09 -0000

vyukov_queue_pool and its variations are not suitable for std::allocate_shared. According to http://en.cppreference.com/w/cpp/memory/shared_ptr/allocate_shared, "this function typically allocates memory for the T object and for the shared_ptr's control block with a single memory allocation".
vyukov_queue_pool is not a general-purpose allocator. It is a free-list - a pool of free fixed-sized block for objects of some type T.

Should be able to create std::shared_ptr with pool_allocator

Anonymous — Thu, 28 Apr 2016 16:05:44 -0000

The following code doesn't compile :

static cds::memory::vyukov_queue_pool<Toto> pool;

    struct PoolAccessor 
    {
        typedef cds::memory::vyukov_queue_pool<Toto>::value_type   value_type;
        cds::memory::vyukov_queue_pool<Toto>& operator()() const
        {
            return pool;
        }
    };

    typedef cds::memory::pool_allocator< Toto, PoolAccessor >   PoolAllocator;

    template<class... TArgs>
    static std::shared_ptr<Toto> createNew(TArgs... args)
    {
        return std::allocate_shared<Toto, PoolAllocator, TArgs...>(PoolAllocator(), std::forward<TArgs>(args)...);
    }

Due to the following static_assert :

static_assert( sizeof(value_type) <= sizeof(typename accessor_type::value_type), "Incompatible type" );

Granted we still can use the overload of the shared_ptr constructor, but in this case, we loose the opimization of make_shared / allocate_shared.

And i'm not sure how to avoid this limitation. Any ideas ?

Recent changes to 19: Should be able to create std::shared_ptr with pool_allocator

#19 Should be able to create std::shared_ptr with pool_allocator

Should be able to create std::shared_ptr with pool_allocator