sysdeps/posix/clock_getres.c

   1 /* clock_getres -- Get the resolution of a POSIX clockid_t.
   2    Copyright (C) 1999,2000,2001,2003,2004,2008 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <stdint.h>
  22 #include <time.h>
  23 #include <unistd.h>
  24 #include <sys/param.h>
  25 #include <libc-internal.h>
  26
  27
  28 #if HP_TIMING_AVAIL
  29 static long int nsec;           /* Clock frequency of the processor.  */
  30
  31 static int
  32 hp_timing_getres (struct timespec *res)
  33 {
  34   if (__builtin_expect (nsec == 0, 0))
  35     {
  36       hp_timing_t freq;
  37
  38       /* This can only happen if we haven't initialized the `nsec'
  39          variable yet.  Do this now.  We don't have to protect this
  40          code against multiple execution since all of them should
  41          lead to the same result.  */
  42       freq = __get_clockfreq ();
  43       if (__builtin_expect (freq == 0, 0))
  44         /* Something went wrong.  */
  45         return -1;
  46
  47       nsec = MAX (UINT64_C (1000000000) / freq, 1);
  48     }
  49
  50   /* Fill in the values.
  51      The seconds are always zero (unless we have a 1Hz machine).  */
  52   res->tv_sec = 0;
  53   res->tv_nsec = nsec;
  54
  55   return 0;
  56 }
  57 #endif
  58
  59 static inline int
  60 realtime_getres (struct timespec *res)
  61 {
  62   long int clk_tck = sysconf (_SC_CLK_TCK);
  63
  64   if (__builtin_expect (clk_tck != -1, 1))
  65     {
  66       /* This implementation assumes that the realtime clock has a
  67          resolution higher than 1 second.  This is the case for any
  68          reasonable implementation.  */
  69       res->tv_sec = 0;
  70       res->tv_nsec = 1000000000 / clk_tck;
  71       return 0;
  72     }
  73
  74   return -1;
  75 }
  76
  77
  78 /* Get resolution of clock.  */
  79 int
  80 clock_getres (clockid_t clock_id, struct timespec *res)
  81 {
  82   int retval = -1;
  83
  84   switch (clock_id)
  85     {
  86 #ifdef SYSDEP_GETRES
  87       SYSDEP_GETRES;
  88 #endif
  89
  90 #ifndef HANDLED_REALTIME
  91     case CLOCK_REALTIME:
  92       retval = realtime_getres (res);
  93       break;
  94 #endif  /* handled REALTIME */
  95
  96     default:
  97 #ifdef SYSDEP_GETRES_CPU
  98       SYSDEP_GETRES_CPU;
  99 #endif
 100 #if HP_TIMING_AVAIL
 101       if ((clock_id & ((1 << CLOCK_IDFIELD_SIZE) - 1))
 102           == CLOCK_THREAD_CPUTIME_ID)
 103         retval = hp_timing_getres (res);
 104       else
 105 #endif
 106         __set_errno (EINVAL);
 107       break;
 108
 109 #if HP_TIMING_AVAIL && !defined HANDLED_CPUTIME
 110     case CLOCK_PROCESS_CPUTIME_ID:
 111     case CLOCK_THREAD_CPUTIME_ID:
 112       retval = hp_timing_getres (res);
 113       break;
 114 #endif
 115     }
 116
 117   return retval;
 118 }