From: "Eregon (Benoit Daloze)" Date: 2013-07-24T01:22:23+09:00 Subject: [ruby-core:56130] [ruby-trunk - Feature #8658] Process.clock_gettime Issue #8658 has been updated by Eregon (Benoit Daloze). akr (Akira Tanaka) wrote: > > While I appreciate Ruby is not always taking the lowest common denominator for functionality (fork, etc), > > we need a counterpart for Windows and OS X at least. > > Users of such OSs can contribute an emulation function for clock_gettime. A very poor one as mapping to Linux/UNIX constants would just confuse people. I do not think the UNIX API clock_gettime() for this is the most suitable, it does not abstract the functionality and the name/usage is not very ruby-like. I think FFI would be a good way if someone need direct access to that low-level C function (except for accessing the constants, that would not be handy). > > naruse gave a very useful link in #8096, http://www.python.org/dev/peps/pep-0418/ . > > I do not wish for a so large API, but I think we should have the timestamp functionality like time.time() > > and a precise performance counter like time.perf_counter(). > > PEP 0418 mentions that python provide clock_gettime as time.clock_gettime. > PEP 0418 doesn't mean providing clock_gettime itself is bad idea. I believe providing a method which is only available in a quite restricted set of platforms is to be avoided. In Python it is simply not defined on non-supporting platforms. > Higer level methods may be useful but what I intend in this issue is a > low level primitive. To which use-cases other than benchmarking do you think? I want Ruby to propose a nice and precise way to benchmark code *not* requiring the user to know about every detail of available clocks/timers under every platform. ---------------------------------------- Feature #8658: Process.clock_gettime https://bugs.ruby-lang.org/issues/8658#change-40625 Author: akr (Akira Tanaka) Status: Open Priority: Normal Assignee: Category: Target version: How about adding a new method, Process.clock_gettime(clk_id) ? Recently there were two feature request for measuring time. Feature #8640 https://bugs.ruby-lang.org/issues/8640 Feature #8096 https://bugs.ruby-lang.org/issues/8096 It seems they are somewhat different. clock_gettime() function defined by POSIX is a good candidate for providing as a method. I think it can supports the both request. Also, it has less possible design choices than the requests because clock_gettime() is defined by POSIX. People familiar to POSIX can learn the method more easily. I wrote a patch to implement Process.clock_gettime. This method can be used as follows. % ./ruby -e 'p Process.clock_gettime(Process::CLOCK_MONOTONIC)' 2701692957811563 Several considerations: I implemented the method as a module function of Process. It is same as Process.times. I expect clock_gettime is used mainly for measuring time interval and wall clock time is not important. So I didn't use Time. The method returns a number of nanoseconds as an integer. It is not so unexpected if user knows clock_gettime() in POSIX. clock_gettime() returns it as struct timespec which contains two fields: tv_sec and tv_nsec. Although tv_sec is time_t, Time is not appropriate because the origin (zero) can be other than the Epoch. Actually CLOCK_MONOTONIC means elapsed time since the system start-up time on Linux. Also, I expect the result is subtracted in most case: t1 = Process.clock_gettime(...) ... t2 = Process.clock_gettime(...) t = t2 - t1 So the result should be easy to subtract. An array such as [sec, nsec] is difficult to subtract. The result is an integer, not a float. IEEE 754 double is not enough to represent the result of clock_gettime(CLOCK_REALTIME). It contains 19 digits in decimal now but IEEE 754 double can represent only 15 digits. On LP64 systems, Fixnum can represent 2**62-1. So (2**62-1)/(365.25*24*60*60*1e9)=146.1 years are representable without object allocation. On ILP32 and LLP64 systems, Fixnum can represent 2**30-1. So (2**30-1)/1e9=1.07 seconds are representable without object allocation. This means Bignum allocations are mostly required except the origin is very recent. clock_gettime() is defined by POSIX. Linux, NetBSD, FreeBSD, OpenBSD has it, at least. If clock_gettime() is not available, an emulation layer for CLOCK_REALTIME is implementable using gettimeofday(). (not implemented yet, though.) Any comments? -- http://bugs.ruby-lang.org/