sysdeps/posix/clock_getres.c

   1 /* clock_getres -- Get the resolution of a POSIX clockid_t.
   2    Copyright (C) 1999-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <stdint.h>
  21 #include <time.h>
  22 #include <unistd.h>
  23 #include <sys/param.h>
  24 #include <libc-internal.h>
  25 #include <shlib-compat.h>
  26
  27 static inline int
  28 realtime_getres (struct timespec *res)
  29 {
  30   long int clk_tck = __sysconf (_SC_CLK_TCK);
  31
  32   if (__glibc_likely (clk_tck != -1))
  33     {
  34       /* This implementation assumes that the realtime clock has a
  35          resolution higher than 1 second.  This is the case for any
  36          reasonable implementation.  */
  37       res->tv_sec = 0;
  38       res->tv_nsec = 1000000000 / clk_tck;
  39       return 0;
  40     }
  41
  42   return -1;
  43 }
  44
  45
  46 /* Get resolution of clock.  */
  47 int
  48 __clock_getres (clockid_t clock_id, struct timespec *res)
  49 {
  50   int retval = -1;
  51
  52   switch (clock_id)
  53     {
  54     case CLOCK_REALTIME:
  55       retval = realtime_getres (res);
  56       break;
  57
  58     default:
  59       __set_errno (EINVAL);
  60       break;
  61     }
  62
  63   return retval;
  64 }
  65
  66 versioned_symbol (libc, __clock_getres, clock_getres, GLIBC_2_17);
  67 /* clock_getres moved to libc in version 2.17;
  68    old binaries may expect the symbol version it had in librt.  */
  69 #if SHLIB_COMPAT (libc, GLIBC_2_2, GLIBC_2_17)
  70 strong_alias (__clock_getres, __clock_getres_2);
  71 compat_symbol (libc, __clock_getres_2, clock_getres, GLIBC_2_2);
  72 #endif