nptl/pthread_clock_gettime.c

   1 /* Copyright (C) 2001-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If
  16    not, see <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <stdlib.h>
  20 #include <time.h>
  21 #include "pthreadP.h"
  22
  23
  24 #if HP_TIMING_AVAIL
  25 int
  26 __pthread_clock_gettime (clockid_t clock_id, hp_timing_t freq,
  27                          struct timespec *tp)
  28 {
  29   hp_timing_t tsc;
  30
  31   /* Get the current counter.  */
  32   HP_TIMING_NOW (tsc);
  33
  34   /* This is the ID of the thread we are looking for.  */
  35   pid_t tid = ((unsigned int) clock_id) >> CLOCK_IDFIELD_SIZE;
  36
  37   /* Compute the offset since the start time of the process.  */
  38   if (tid == 0 || tid == THREAD_GETMEM (THREAD_SELF, tid))
  39     /* Our own clock.  */
  40     tsc -= THREAD_GETMEM (THREAD_SELF, cpuclock_offset);
  41   else
  42     {
  43       /* This is more complicated.  We have to locate the thread based
  44          on the ID.  This means walking the list of existing
  45          threads.  */
  46       struct pthread *thread = __find_thread_by_id (tid);
  47       if (thread == NULL)
  48         {
  49           __set_errno (EINVAL);
  50           return -1;
  51         }
  52
  53       /* There is a race here.  The thread might terminate and the stack
  54          become unusable.  But this is the user's problem.  */
  55       tsc -= thread->cpuclock_offset;
  56     }
  57
  58   /* Compute the seconds.  */
  59   tp->tv_sec = tsc / freq;
  60
  61   /* And the nanoseconds.  This computation should be stable until
  62      we get machines with about 16GHz frequency.  */
  63   tp->tv_nsec = ((tsc % freq) * 1000000000ull) / freq;
  64
  65   return 0;
  66 }
  67 #endif