nptl/pthread_rwlock_timedrdlock.c

   1 /* Copyright (C) 2003-2014 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
  25
  26 /* Try to acquire read lock for RWLOCK or return after specfied time.  */
  27 int
  28 pthread_rwlock_timedrdlock (rwlock, abstime)
  29      pthread_rwlock_t *rwlock;
  30      const struct timespec *abstime;
  31 {
  32   int result = 0;
  33
  34   /* Make sure we are alone.  */
  35   lll_lock(rwlock->__data.__lock, rwlock->__data.__shared);
  36
  37   while (1)
  38     {
  39       int err;
  40
  41       /* Get the rwlock if there is no writer...  */
  42       if (rwlock->__data.__writer == 0
  43           /* ...and if either no writer is waiting or we prefer readers.  */
  44           && (!rwlock->__data.__nr_writers_queued
  45               || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
  46         {
  47           /* Increment the reader counter.  Avoid overflow.  */
  48           if (++rwlock->__data.__nr_readers == 0)
  49             {
  50               /* Overflow on number of readers.  */
  51               --rwlock->__data.__nr_readers;
  52               result = EAGAIN;
  53             }
  54
  55           break;
  56         }
  57
  58       /* Make sure we are not holding the rwlock as a writer.  This is
  59          a deadlock situation we recognize and report.  */
  60       if (__builtin_expect (rwlock->__data.__writer
  61                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  62         {
  63           result = EDEADLK;
  64           break;
  65         }
  66
  67       /* Make sure the passed in timeout value is valid.  Ideally this
  68          test would be executed once.  But since it must not be
  69          performed if we would not block at all simply moving the test
  70          to the front is no option.  Replicating all the code is
  71          costly while this test is not.  */
  72       if (__builtin_expect (abstime->tv_nsec >= 1000000000
  73                             || abstime->tv_nsec < 0, 0))
  74         {
  75           result = EINVAL;
  76           break;
  77         }
  78
  79       /* Work around the fact that the kernel rejects negative timeout values
  80          despite them being valid.  */
  81       if (__builtin_expect (abstime->tv_sec < 0, 0))
  82         {
  83           result = ETIMEDOUT;
  84           break;
  85         }
  86
  87 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
  88      || !defined lll_futex_timed_wait_bitset)
  89       /* Get the current time.  So far we support only one clock.  */
  90       struct timeval tv;
  91       (void) gettimeofday (&tv, NULL);
  92
  93       /* Convert the absolute timeout value to a relative timeout.  */
  94       struct timespec rt;
  95       rt.tv_sec = abstime->tv_sec - tv.tv_sec;
  96       rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
  97       if (rt.tv_nsec < 0)
  98         {
  99           rt.tv_nsec += 1000000000;
 100           --rt.tv_sec;
 101         }
 102       /* Did we already time out?  */
 103       if (rt.tv_sec < 0)
 104         {
 105           /* Yep, return with an appropriate error.  */
 106           result = ETIMEDOUT;
 107           break;
 108         }
 109 #endif
 110
 111       /* Remember that we are a reader.  */
 112       if (++rwlock->__data.__nr_readers_queued == 0)
 113         {
 114           /* Overflow on number of queued readers.  */
 115           --rwlock->__data.__nr_readers_queued;
 116           result = EAGAIN;
 117           break;
 118         }
 119
 120       int waitval = rwlock->__data.__readers_wakeup;
 121
 122       /* Free the lock.  */
 123       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 124
 125       /* Wait for the writer to finish.  */
 126 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
 127      || !defined lll_futex_timed_wait_bitset)
 128       err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup,
 129                                   waitval, &rt, rwlock->__data.__shared);
 130 #else
 131       err = lll_futex_timed_wait_bitset (&rwlock->__data.__readers_wakeup,
 132                                          waitval, abstime,
 133                                          FUTEX_CLOCK_REALTIME,
 134                                          rwlock->__data.__shared);
 135 #endif
 136
 137       /* Get the lock.  */
 138       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 139
 140       --rwlock->__data.__nr_readers_queued;
 141
 142       /* Did the futex call time out?  */
 143       if (err == -ETIMEDOUT)
 144         {
 145           /* Yep, report it.  */
 146           result = ETIMEDOUT;
 147           break;
 148         }
 149     }
 150
 151   /* We are done, free the lock.  */
 152   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 153
 154   return result;
 155 }