Re: [boost] [function] function wrapping with noexceptionsafetyguarantee

Subject: Re: [boost] [function] function wrapping with noexceptionsafetyguarantee
From: Emil Dotchevski (emil_at_[hidden])
Date: 2010-10-25 17:17:44

On Mon, Oct 25, 2010 at 1:54 PM, Daniel Walker
<daniel.j.walker_at_[hidden]> wrote:
> On Sat, Oct 23, 2010 at 3:00 PM, Domagoj Saric <dsaritz_at_[hidden]> wrote:
>>
>> "Daniel Walker" <daniel.j.walker_at_[hidden]> wrote in message
>> news:AANLkTikXL0i5Z+NoO2a3TiB8q2RmTk4oHJ1kzOyR-7vE_at_mail.gmail.com...
>>>
>>> Do you have any suggestion for how to quantify this? I've run some
>>> simple benchmarks, but in optimized object code the time overhead of
>>> boost::function is so small it's hard to measure.
>>
>> Those benchmarks are obviously lacking...I've given you examples that show
>> that the various overheads of the current implementation are quite
>> measurable...
>
> Sorry, I must have missed your examples. Here's a simple benchmark
> that we could use:
>
> template<class T>
> double benchmark(T f, int n)
> {
>    assert(f);
>    boost::timer t;
>    for(int i = 0; i < n; ++i)
>        f(i);
>    return t.elapsed();
> }
>
> int echo(int x) { return x; }
>
> int main()
> {
>    int n = INT_MAX;
>    boost::function<int(int)> f = &echo;
>
>    double baseline = benchmark(&echo, n);
>    double t = benchmark(f, n);
>    assert(baseline < t);
>
>    std::cout << "boost::function overhead = "
>              << (t - baseline) / n << " seconds"
>              << std::endl;
>    return 0;
> }
>
> On my machine, this measures the overhead of boost::function as 2
> nanoseconds, though, obviously, this is a statistical inference and
> quantities of time that small are hard to measure.

I've found that such benchmarks, while able to produce long mailing
list discussions, don't have much practical value. Do you have a
performance problem with the current boost::function? An actual
program or application which would run noticeably faster with the 2
nanoseconds per call speedup?

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode