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POextending the std::chrono functionality to deal with run-time (non compile-time) constant periods
 

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  1. POextending the std::chrono functionality to deal with run-time (non compile-time) constant periods
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    <p>I have been experimenting with all kind of timers on Linux and OSX, and would like to try and wrap some of them with the same interface used by std::chrono.</p> <p>That's easy to do for timers that have a well-defined "period" at compile time, e.g. the POSIX clock_gettime() familiy, the clock_get_time() family on OSX, or gettimeofday().</p> <p>However, there are some useful timers for which the "period" - while constant - is only known at runtime. For example: - POSIX states the period of clock(), CLOCKS_PER_SEC, may be a variable on non-XSI systems - on Linux, the period of times() is given at runtime by sysconf(_SC_CLK_TCK) - on OSX, the period of mach_absolute_time() is given at runtime by mach_timebase_info() - on recent Intel processors, the DST register ticks at a constant rate, but of course that can only be determined at runtime</p> <p>To wrap these timers in the std::chrono interface, one possibility would be to use a period of std::chrono::nanosecond , and convert the value of each timer to nanoseconds. An other approach could be to use a floating point representation. However, both approaches would introduce a (very small) overhead to the now() function, and a (probably small) loss in precision.</p> <p>The solution I'm trying to pursue is to define a set of classes to represent such "run-time constant" periods, built along the same lines as the std::ratio class. However I expect that will require rewriting all the related template classes and functions (as they assume constexpr values).</p> <p>Does anyone have any experience with wrapping these kind of timers a la std:chrono ?</p> <p>Or with using non-constexpr values for the time period of a clock ?</p>
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