On 16/06/2011 06:43, Stephan T. Lavavej wrote:
[Peter Dimov]
My initial implementation of boost::make_shared was a self-contained header that didn't require any changes to shared_ptr (it would have worked with std::tr1::shared_ptr as well as it worked with boost::shared_ptr). This can only be done with a free function.
Aha - that's an interesting bit of history!
(However, it can be argued that this support - the ability to ask for a deleter of a specific type to be default-constructed in place by shared_ptr - should be offered to users as well, not just to make_shared.)
I don't look at Boost's implementation, but this makes me curious as to whether you implement the "we know where you live" optimization. On x86, for a 4-byte Foobar, how big is your reference count control block for make_shared<Foobar>()? Mine is 16 bytes.
What's the point? It still need to be padded to 32 for good performance and to use DWCAS.