nptl/lowlevelrobustlock.c

   1 /* Copyright (C) 2006-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Jakub Jelinek <jakub@redhat.com>, 2006.
   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 <sysdep.h>
  21 #include <lowlevellock.h>
  22 #include <sys/time.h>
  23 #include <pthreadP.h>
  24 #include <kernel-features.h>
  25
  26
  27 int
  28 __lll_robust_lock_wait (int *futex, int private)
  29 {
  30   int oldval = *futex;
  31   int tid = THREAD_GETMEM (THREAD_SELF, tid);
  32
  33   /* If the futex changed meanwhile try locking again.  */
  34   if (oldval == 0)
  35     goto try;
  36
  37   do
  38     {
  39       /* If the owner died, return the present value of the futex.  */
  40       if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
  41         return oldval;
  42
  43       /* Try to put the lock into state 'acquired, possibly with waiters'.  */
  44       int newval = oldval | FUTEX_WAITERS;
  45       if (oldval != newval
  46           && atomic_compare_and_exchange_bool_acq (futex, newval, oldval))
  47         continue;
  48
  49       /* If *futex == 2, wait until woken.  */
  50       lll_futex_wait (futex, newval, private);
  51
  52     try:
  53       ;
  54     }
  55   while ((oldval = atomic_compare_and_exchange_val_acq (futex,
  56                                                         tid | FUTEX_WAITERS,
  57                                                         0)) != 0);
  58   return 0;
  59 }
  60
  61
  62 int
  63 __lll_robust_timedlock_wait (int *futex, const struct timespec *abstime,
  64                              int private)
  65 {
  66   /* Reject invalid timeouts.  */
  67   if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
  68     return EINVAL;
  69
  70   int tid = THREAD_GETMEM (THREAD_SELF, tid);
  71   int oldval = *futex;
  72
  73   /* If the futex changed meanwhile, try locking again.  */
  74   if (oldval == 0)
  75     goto try;
  76
  77   /* Work around the fact that the kernel rejects negative timeout values
  78      despite them being valid.  */
  79   if (__glibc_unlikely (abstime->tv_sec < 0))
  80     return ETIMEDOUT;
  81
  82   do
  83     {
  84 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
  85      || !defined lll_futex_timed_wait_bitset)
  86       struct timeval tv;
  87       struct timespec rt;
  88
  89       /* Get the current time.  */
  90       (void) __gettimeofday (&tv, NULL);
  91
  92       /* Compute relative timeout.  */
  93       rt.tv_sec = abstime->tv_sec - tv.tv_sec;
  94       rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
  95       if (rt.tv_nsec < 0)
  96         {
  97           rt.tv_nsec += 1000000000;
  98           --rt.tv_sec;
  99         }
 100
 101       /* Already timed out?  */
 102       if (rt.tv_sec < 0)
 103         return ETIMEDOUT;
 104 #endif
 105
 106       /* If the owner died, return the present value of the futex.  */
 107       if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
 108         return oldval;
 109
 110       /* Try to put the lock into state 'acquired, possibly with waiters'.  */
 111       int newval = oldval | FUTEX_WAITERS;
 112       if (oldval != newval
 113           && atomic_compare_and_exchange_bool_acq (futex, newval, oldval))
 114         continue;
 115
 116       /* If *futex == 2, wait until woken or timeout.  */
 117 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
 118      || !defined lll_futex_timed_wait_bitset)
 119       lll_futex_timed_wait (futex, newval, &rt, private);
 120 #else
 121       lll_futex_timed_wait_bitset (futex, newval, abstime,
 122                                    FUTEX_CLOCK_REALTIME, private);
 123 #endif
 124
 125     try:
 126       ;
 127     }
 128   while ((oldval = atomic_compare_and_exchange_val_acq (futex,
 129                                                         tid | FUTEX_WAITERS,
 130                                                         0)) != 0);
 131
 132   return 0;
 133 }