Re: [boost] [Chrono] Proposed library now feature complete

Subject: Re: [boost] [Chrono] Proposed library now feature complete
From: Howard Hinnant (hinnant_at_[hidden])
Date: 2008-11-18 19:56:10

On Nov 18, 2008, at 9:14 AM, Beman Dawes wrote:

> The Chrono library in the sandbox is now more-or-less feature  
> complete. In addition to the C++0x features, timers have been added  
> to replace the old Boost.Timer library which will become deprecated.
>
> The feature list includes:
>
>   *  The C++0x Standard Library's time utilities, including:
>         o Class template duration
>         o Class template time_point
>         o Clocks:
>               + |system_clock|
>               + |monotonic_clock|
>               + |high_resolution_clock|
>                     * Class template |timer|, with typedefs:
>         o |system_timer|
>         o |monotonic_timer|
>         o |high_resolution_timer|
>               * Process clocks and timers:
>         o |process_clock|, capturing real, user-CPU, and system-CPU  
> times.
>         o |process_timer|, capturing elapsed real, user-CPU, and
>           system-CPU times.
>         o |run_timer|, convenient reporting of |process_timer|  
> results.
>               *  The C++0x Standard Library's compile-time rational  
> arithmetic.
>
> See http://svn.boost.org/svn/boost/sandbox/chrono
>
> The implementation is now working and lightly tested on Windows with  
> VC++ 9.0 SP1 and Intel ia32 11.0 compilers, and on Ubuntu Linux with  
> GCC 4.2.4 compiler.
>
> There is a bit more documentation, but it is still needs much work.
>
> Comments are welcome.

It seems a shame that process_clock does not really meet the proposed  
standard clock requirements (its now() doesn't return the  
time_point).  That being said, I can see why you didn't.  This clock  
really has 3 distinct "time points" and one needs to set each of those  
three with one system call.  If one wanted, one could easily create a  
user_time_clock wrapper around processor_clock to adapt it to the  
standard clock requirements if needed.

Just for general education purposes, here's a portable processor-time  
clock (just to show how easy it is to build a custom clock):

#include <ctime>
#include <cstdio>
#include <chrono>

class processor_clock
{
public:
     typedef std::clock_t                             rep;
     typedef std::ratio<1, CLOCKS_PER_SEC>            period;
     typedef std::chrono::duration<rep, period>       duration;
     typedef std::chrono::time_point<processor_clock> time_point;
     static const bool is_monotonic =                 true;

     static time_point now() {return  
time_point(duration(std::clock()));}
};

int main()
{
     processor_clock::time_point t1 = processor_clock::now();
     processor_clock::time_point t2 = processor_clock::now();
     std::printf("%g seconds\n", std::chrono::duration<double>(t2- 
t1).count());
}

Output:

4e-06 seconds

-Howard