nptl/pthread_rwlock_timedrdlock.c

   1 /* Copyright (C) 2003-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
   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 <pthread.h>
  23 #include <pthreadP.h>
  24 #include <sys/time.h>
  25 #include <kernel-features.h>
  26 #include <stdbool.h>
  27
  28
  29 /* Try to acquire read lock for RWLOCK or return after specfied time.  */
  30 int
  31 pthread_rwlock_timedrdlock (rwlock, abstime)
  32      pthread_rwlock_t *rwlock;
  33      const struct timespec *abstime;
  34 {
  35   int result = 0;
  36   bool wake = false;
  37
  38   /* Make sure we are alone.  */
  39   lll_lock(rwlock->__data.__lock, rwlock->__data.__shared);
  40
  41   while (1)
  42     {
  43       int err;
  44
  45       /* Get the rwlock if there is no writer...  */
  46       if (rwlock->__data.__writer == 0
  47           /* ...and if either no writer is waiting or we prefer readers.  */
  48           && (!rwlock->__data.__nr_writers_queued
  49               || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
  50         {
  51           /* Increment the reader counter.  Avoid overflow.  */
  52           if (++rwlock->__data.__nr_readers == 0)
  53             {
  54               /* Overflow on number of readers.  */
  55               --rwlock->__data.__nr_readers;
  56               result = EAGAIN;
  57             }
  58           else
  59             {
  60               /* See pthread_rwlock_rdlock.  */
  61               if (rwlock->__data.__nr_readers == 1
  62                   && rwlock->__data.__nr_readers_queued > 0
  63                   && rwlock->__data.__nr_writers_queued > 0)
  64                 {
  65                   ++rwlock->__data.__readers_wakeup;
  66                   wake = true;
  67                 }
  68             }
  69
  70           break;
  71         }
  72
  73       /* Make sure we are not holding the rwlock as a writer.  This is
  74          a deadlock situation we recognize and report.  */
  75       if (__builtin_expect (rwlock->__data.__writer
  76                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  77         {
  78           result = EDEADLK;
  79           break;
  80         }
  81
  82       /* Make sure the passed in timeout value is valid.  Ideally this
  83          test would be executed once.  But since it must not be
  84          performed if we would not block at all simply moving the test
  85          to the front is no option.  Replicating all the code is
  86          costly while this test is not.  */
  87       if (__builtin_expect (abstime->tv_nsec >= 1000000000
  88                             || abstime->tv_nsec < 0, 0))
  89         {
  90           result = EINVAL;
  91           break;
  92         }
  93
  94       /* Work around the fact that the kernel rejects negative timeout values
  95          despite them being valid.  */
  96       if (__glibc_unlikely (abstime->tv_sec < 0))
  97         {
  98           result = ETIMEDOUT;
  99           break;
 100         }
 101
 102 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
 103      || !defined lll_futex_timed_wait_bitset)
 104       /* Get the current time.  So far we support only one clock.  */
 105       struct timeval tv;
 106       (void) __gettimeofday (&tv, NULL);
 107
 108       /* Convert the absolute timeout value to a relative timeout.  */
 109       struct timespec rt;
 110       rt.tv_sec = abstime->tv_sec - tv.tv_sec;
 111       rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
 112       if (rt.tv_nsec < 0)
 113         {
 114           rt.tv_nsec += 1000000000;
 115           --rt.tv_sec;
 116         }
 117       /* Did we already time out?  */
 118       if (rt.tv_sec < 0)
 119         {
 120           /* Yep, return with an appropriate error.  */
 121           result = ETIMEDOUT;
 122           break;
 123         }
 124 #endif
 125
 126       /* Remember that we are a reader.  */
 127       if (++rwlock->__data.__nr_readers_queued == 0)
 128         {
 129           /* Overflow on number of queued readers.  */
 130           --rwlock->__data.__nr_readers_queued;
 131           result = EAGAIN;
 132           break;
 133         }
 134
 135       int waitval = rwlock->__data.__readers_wakeup;
 136
 137       /* Free the lock.  */
 138       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 139
 140       /* Wait for the writer to finish.  */
 141 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
 142      || !defined lll_futex_timed_wait_bitset)
 143       err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup,
 144                                   waitval, &rt, rwlock->__data.__shared);
 145 #else
 146       err = lll_futex_timed_wait_bitset (&rwlock->__data.__readers_wakeup,
 147                                          waitval, abstime,
 148                                          FUTEX_CLOCK_REALTIME,
 149                                          rwlock->__data.__shared);
 150 #endif
 151
 152       /* Get the lock.  */
 153       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 154
 155       --rwlock->__data.__nr_readers_queued;
 156
 157       /* Did the futex call time out?  */
 158       if (err == -ETIMEDOUT)
 159         {
 160           /* Yep, report it.  */
 161           result = ETIMEDOUT;
 162           break;
 163         }
 164     }
 165
 166   /* We are done, free the lock.  */
 167   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 168
 169   if (wake)
 170     lll_futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
 171                     rwlock->__data.__shared);
 172
 173   return result;
 174 }