sysdeps/posix/clock_getres.c

   1 /* clock_getres -- Get the resolution of a POSIX clockid_t.
   2    Copyright (C) 1999-2015 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
  26
  27 #if HP_TIMING_AVAIL
  28 static long int nsec;           /* Clock frequency of the processor.  */
  29
  30 static int
  31 hp_timing_getres (struct timespec *res)
  32 {
  33   if (__glibc_unlikely (nsec == 0))
  34     {
  35       hp_timing_t freq;
  36
  37       /* This can only happen if we haven't initialized the `nsec'
  38          variable yet.  Do this now.  We don't have to protect this
  39          code against multiple execution since all of them should
  40          lead to the same result.  */
  41       freq = __get_clockfreq ();
  42       if (__glibc_unlikely (freq == 0))
  43         /* Something went wrong.  */
  44         return -1;
  45
  46       nsec = MAX (UINT64_C (1000000000) / freq, 1);
  47     }
  48
  49   /* Fill in the values.
  50      The seconds are always zero (unless we have a 1Hz machine).  */
  51   res->tv_sec = 0;
  52   res->tv_nsec = nsec;
  53
  54   return 0;
  55 }
  56 #endif
  57
  58 static inline int
  59 realtime_getres (struct timespec *res)
  60 {
  61   long int clk_tck = sysconf (_SC_CLK_TCK);
  62
  63   if (__glibc_likely (clk_tck != -1))
  64     {
  65       /* This implementation assumes that the realtime clock has a
  66          resolution higher than 1 second.  This is the case for any
  67          reasonable implementation.  */
  68       res->tv_sec = 0;
  69       res->tv_nsec = 1000000000 / clk_tck;
  70       return 0;
  71     }
  72
  73   return -1;
  74 }
  75
  76
  77 /* Get resolution of clock.  */
  78 int
  79 __clock_getres (clockid_t clock_id, struct timespec *res)
  80 {
  81   int retval = -1;
  82
  83   switch (clock_id)
  84     {
  85 #ifdef SYSDEP_GETRES
  86       SYSDEP_GETRES;
  87 #endif
  88
  89 #ifndef HANDLED_REALTIME
  90     case CLOCK_REALTIME:
  91       retval = realtime_getres (res);
  92       break;
  93 #endif  /* handled REALTIME */
  94
  95     default:
  96 #ifdef SYSDEP_GETRES_CPU
  97       SYSDEP_GETRES_CPU;
  98 #endif
  99 #if HP_TIMING_AVAIL
 100       if ((clock_id & ((1 << CLOCK_IDFIELD_SIZE) - 1))
 101           == CLOCK_THREAD_CPUTIME_ID)
 102         retval = hp_timing_getres (res);
 103       else
 104 #endif
 105         __set_errno (EINVAL);
 106       break;
 107
 108 #if HP_TIMING_AVAIL && !defined HANDLED_CPUTIME
 109     case CLOCK_PROCESS_CPUTIME_ID:
 110     case CLOCK_THREAD_CPUTIME_ID:
 111       retval = hp_timing_getres (res);
 112       break;
 113 #endif
 114     }
 115
 116   return retval;
 117 }
 118 weak_alias (__clock_getres, clock_getres)