Re: [boost] "Small buffer optimization" for boost::function?

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-12-28 15:14:07

Vladimir Prus wrote:
> Alex Besogonov wrote:
>
>> Vladimir Prus wrote:
>>>> This optimization will make boost::function _much_ faster - in one
>>>> of
>>> How much faster, exactly? Recently, in a thread "[signal]
>>> performance" I've posted a small benchmark that finds
>>> boost::function to take 4 times more time that call via function
>>> pointer -- which, IMO, is pretty fast.
>
>> I don't have any problem with boost::function speed of invocations
>> (though FastDelegate is two times faster).
>
> I see. Still, would be nice to see specific numbers.

I like timing the copy contructor of various types. :-)

8M push_back operations in an unreserved vector for:

shared_ptr: 1.6
function<> holding a function pointer: 1.6
POD with size 64: 4.9
function<> holding a trivial function object: 17.6

So, assuming that function<> is more frequently used with function objects, 
SBO would be a win even for size 128. This is with a "bad" ::operator new 
(the one from MSVC 7.1 MT lib), but still...