python, time and sleep

gistfile1.py

# -*- coding: utf-8 -*-
from __future__ import absolute_import, print_function, unicode_literals

from select import select
from cffi import FFI


ffi = FFI()
ffi.cdef("""
#define CLOCK_REALTIME ...
#define CLOCK_MONOTONIC ...
#define CLOCK_PROCESS_CPUTIME_ID ...
#define CLOCK_THREAD_CPUTIME_ID ...
#define CLOCK_MONOTONIC_RAW ...
#define CLOCK_REALTIME_COARSE ...
#define CLOCK_MONOTONIC_COARSE ...
#define CLOCK_BOOTTIME ...

typedef int clockid_t;

struct timespec
{
    long tv_sec;            /* Seconds.  */
    long tv_nsec;  /* Nanoseconds.  */
};

int clock_getres (clockid_t __clock_id, struct timespec *__res);
int clock_gettime (clockid_t __clock_id, struct timespec *__tp);
int clock_settime (clockid_t __clock_id, const struct timespec *__tp);

int nanosleep (const struct timespec *__requested_time,
               struct timespec       *__remaining);
""")

ffi_lib = ffi.verify("""
#include <time.h>
""", libraries=['rt', ])


def _ts_to_float(ts):
    return ts.tv_sec + ts.tv_nsec / 1e9


def nano_sleep(value):
    ts_a = ffi.new('struct timespec *')
    ts_a.tv_sec, ts_a.tv_nsec = int(value), int((value - int(value)) * 1e9)

    ts_b = ffi.new('struct timespec *')
    ffi_lib.nanosleep(ts_a, ts_b)
    return _ts_to_float(ts_b)


def clock_get_resolution(clock_id):
    ts = ffi.new('struct timespec *')
    if ffi_lib.clock_getres(clock_id, ts) < 0:
        raise OSError(ffi.errno, 'clock_getres failed')
    return _ts_to_float(ts)


def clock_get_time(clock_id):
    ts = ffi.new('struct timespec *')
    if ffi_lib.clock_gettime(clock_id, ts) < 0:
        raise OSError(ffi.errno, 'clock_gettime failed')
    return _ts_to_float(ts)


def monotonic():
    return clock_get_time(ffi_lib.CLOCK_MONOTONIC)


while True:
    a = monotonic()
    nano_sleep(3.)
    b = monotonic()
    print('nsleep:', b - a)

    a = monotonic()
    select([], [], [], 3.)
    b = monotonic()
    print('select:', b - a)