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