Re: [boost] [function] function wrapping withnoexceptionsafetyguarantee

Subject: Re: [boost] [function] function wrapping withnoexceptionsafetyguarantee
From: Jeffrey Lee Hellrung, Jr. (jhellrung_at_[hidden])
Date: 2010-11-06 17:31:37

On 11/6/2010 10:22 AM, Daniel Walker wrote:
> On Tue, Nov 2, 2010 at 7:20 PM, Jeffrey Lee Hellrung, Jr.
> <jhellrung_at_[hidden]>  wrote:
>> On 11/02/2010 02:50 PM, Daniel Walker wrote:
>> [...]
>>>
>>> Here are the results I got, again, using the build of g++ 4.2 provided
>>> by my manufacturer.
>>>
>>> Data (Release):
>>>             |  function   | function (static empty)
>>> time/call  |  3.54e-07s  |  3.51e-07s
>>> space/type |    64B      |    80B
>>>
>>> Data (Debug):
>>>             |  function   | function (static empty)
>>> time/call  |  2.05e-06s  |  2.04e-06s
>>> space/type |    64B      |    80B
>>>
>>> You can see that removing the empty check from boost::function yields
>>> about a 1% improvement in time per call to boost::signal. The
>>> increased space per type overhead is the same as before: 16B.
>>
>> [...]
>>
>> [Butting in after only vaguely following this thread...]
>>
>> Would it also be appropriate to measure the "space/call", in addition to
>> "time/call" and "space/type"?  Or is there no difference, or had this been
>> addressed already?
>
> Well, a call to boost::function does not cost any additional space.

I'm not sure what you mean.  "Additional" to what?

Isn't the underlying dispatching code different for the 2 
implementations of boost::function you're comparing above?  I.e., one 
has a null-pointer check, while the other doesn't.  One might 
hypothesize that the dispatching code that must perform a null-pointer 
check will compile to more instructions than the dispatching code that 
does not perform a null-pointer check, and I presume the timings above 
support this hypothesis.  I would think this should lead to variations 
in the size of the code segment.  This variation might be more 
pronounced if the dispatching were inlined.  I'm just speculating...

- Jeff