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times: use clock_gettime for cpuTime with POSIX (#9793)

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The POSIX 'clock()' procedure returns process CPU time in an
implementation specific unit, which for historical reasons can be as
large as ~7ms in the case of FreeBSD. Use 'clock_gettime' for higher
accuracy.
This commit is contained in:
Emery Hemingway 2018-11-26 17:00:17 +01:00 • committed by Andreas Rumpf
commit ed8b4befbf
1 changed files with 13 additions and 3 deletions
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16
lib/pure/times.nim
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@ -158,7 +158,9 @@ when defined(posix):
type CTime = posix.Time type CTime = posix.Time
var CLOCK_REALTIME {.importc: "CLOCK_REALTIME", header: "<time.h>".}: Clockid var
realTimeClockId {.importc: "CLOCK_REALTIME", header: "<time.h>".}: Clockid
cpuClockId {.importc: "CLOCK_THREAD_CPUTIME_ID", header: "<time.h>".}: Clockid
proc gettimeofday(tp: var Timeval, unused: pointer = nil) {. proc gettimeofday(tp: var Timeval, unused: pointer = nil) {.
importc: "gettimeofday", header: "<sys/time.h>".} importc: "gettimeofday", header: "<sys/time.h>".}
@ -1065,7 +1067,7 @@ proc getTime*(): Time {.tags: [TimeEffect], benign.} =
result = initTime(a.tv_sec.int64, convert(Microseconds, Nanoseconds, a.tv_usec.int)) result = initTime(a.tv_sec.int64, convert(Microseconds, Nanoseconds, a.tv_usec.int))
elif defined(posix): elif defined(posix):
var ts: Timespec var ts: Timespec
discard clock_gettime(CLOCK_REALTIME, ts) discard clock_gettime(realTimeClockId, ts)
result = initTime(ts.tv_sec.int64, ts.tv_nsec.int) result = initTime(ts.tv_sec.int64, ts.tv_nsec.int)
elif defined(windows): elif defined(windows):
var f: FILETIME var f: FILETIME
@ -2337,7 +2339,15 @@ when not defined(JS):
fib.add(fib[^1] + fib[^2]) fib.add(fib[^1] + fib[^2])
echo "CPU time [s] ", cpuTime() - t0 echo "CPU time [s] ", cpuTime() - t0
echo "Fib is [s] ", fib echo "Fib is [s] ", fib
result = toFloat(int(getClock())) / toFloat(clocksPerSec) when defined(posix):
# 'clocksPerSec' is a compile-time constant, possibly a
# rather awful one, so use clock_gettime instead
var ts: Timespec
discard clock_gettime(cpuClockId, ts)
result = toFloat(ts.tv_sec.int) +
toFloat(ts.tv_nsec.int) / 1_000_000_000
else:
result = toFloat(int(getClock())) / toFloat(clocksPerSec)
proc epochTime*(): float {.rtl, extern: "nt$1", tags: [TimeEffect].} = proc epochTime*(): float {.rtl, extern: "nt$1", tags: [TimeEffect].} =
## gets time after the UNIX epoch (1970) in seconds. It is a float ## gets time after the UNIX epoch (1970) in seconds. It is a float