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

Subject: Re: [boost] [function] function wrapping with noexceptionsafetyguarantee
From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2010-10-25 16:54:58

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.

Does anyone have other suggestions for how to benchmark boost::function?

Daniel Walker