From: "akr (Akira Tanaka)" Date: 2013-07-20T19:39:19+09:00 Subject: [ruby-core:56092] [ruby-trunk - Feature #8658] Process.clock_gettime Issue #8658 has been updated by akr (Akira Tanaka). File clock_gettime-2.patch added kosaki (Motohiro KOSAKI) wrote: > First, Process.times() returns user time and system time and they are process specific. But Process::CLOCK_MONOTONIC is not per-process time. Yes. Users can choose any clock with Process.clock_gettime unlike other proposals (#8640, #8096). It seems many people use CLOCK_REALTIME to measure a time interval, though. > Second, Linux's CLOCK_MONOTONIC_RAW has the same behavior BSD's CLOCK_MONOTONIC. And, an application which measures a performance need to use CLOCK_MONOTONIC_RAW for avoiding ntp confusing. Then, we should do 1) exporse CLOCK_MONOTONIC_RAW or 2) Process.clock_gettime(Process::CLOCK_MONOTONIC) uses CLOCK_MONOTONIC_RAW internally. OS specific CLOCK_* constants can be defined. Since Process.clock_gettime is a primitive, exchange clk_id is not a good idea. > Third, using float is a good ruby convention. If we need to use inter (for precision and performance?), the method should have a precision explanation, likes get_time_nanosecond. I mean, ruby interpreter can't warn nor detect following mistake. > > a = foo # this is usec > b = bar # this is nsec > c = a + b > > then, we should warn by method name verbosely. IMHO. Hm. It is acceptable as far as the exact result (number of nanoseconds) can be obtained. After thinking while, I find Process.clock_gettime(clk_id, unit). unit is an optional argument and :nanoseconds specifies the nanoseconds. This can help performance on ILP33 because :microseconds with CLOCK_PROCESS_CPUTIME_ID will not use Bignum until 1073 seconds after process start up. I updated the patch. ---------------------------------------- Feature #8658: Process.clock_gettime https://bugs.ruby-lang.org/issues/8658#change-40590 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/