nptl/pthread_rwlock_timedwrlock.c

   1 /* Copyright (C) 2003-2012 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 write lock for RWLOCK or return after specfied time.  */
  27 int
  28 pthread_rwlock_timedwrlock (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 and no reader.  */
  42       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  43         {
  44           /* Mark self as writer.  */
  45           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  46           break;
  47         }
  48
  49       /* Make sure we are not holding the rwlock as a writer.  This is
  50          a deadlock situation we recognize and report.  */
  51       if (__builtin_expect (rwlock->__data.__writer
  52                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  53         {
  54           result = EDEADLK;
  55           break;
  56         }
  57
  58       /* Make sure the passed in timeout value is valid.  Ideally this
  59          test would be executed once.  But since it must not be
  60          performed if we would not block at all simply moving the test
  61          to the front is no option.  Replicating all the code is
  62          costly while this test is not.  */
  63       if (__builtin_expect (abstime->tv_nsec >= 1000000000
  64                             || abstime->tv_nsec < 0, 0))
  65         {
  66           result = EINVAL;
  67           break;
  68         }
  69
  70       /* Work around the fact that the kernel rejects negative timeout values
  71          despite them being valid.  */
  72       if (__builtin_expect (abstime->tv_sec < 0, 0))
  73         {
  74           result = ETIMEDOUT;
  75           break;
  76         }
  77
  78 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
  79      || !defined lll_futex_timed_wait_bitset)
  80       /* Get the current time.  So far we support only one clock.  */
  81       struct timeval tv;
  82       (void) gettimeofday (&tv, NULL);
  83
  84       /* Convert the absolute timeout value to a relative timeout.  */
  85       struct timespec rt;
  86       rt.tv_sec = abstime->tv_sec - tv.tv_sec;
  87       rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
  88       if (rt.tv_nsec < 0)
  89         {
  90           rt.tv_nsec += 1000000000;
  91           --rt.tv_sec;
  92         }
  93       /* Did we already time out?  */
  94       if (rt.tv_sec < 0)
  95         {
  96           result = ETIMEDOUT;
  97           break;
  98         }
  99 #endif
 100
 101       /* Remember that we are a writer.  */
 102       if (++rwlock->__data.__nr_writers_queued == 0)
 103         {
 104           /* Overflow on number of queued writers.  */
 105           --rwlock->__data.__nr_writers_queued;
 106           result = EAGAIN;
 107           break;
 108         }
 109
 110       int waitval = rwlock->__data.__writer_wakeup;
 111
 112       /* Free the lock.  */
 113       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 114
 115       /* Wait for the writer or reader(s) to finish.  */
 116 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
 117      || !defined lll_futex_timed_wait_bitset)
 118       err = lll_futex_timed_wait (&rwlock->__data.__writer_wakeup,
 119                                   waitval, &rt, rwlock->__data.__shared);
 120 #else
 121       err = lll_futex_timed_wait_bitset (&rwlock->__data.__writer_wakeup,
 122                                          waitval, abstime,
 123                                          FUTEX_CLOCK_REALTIME,
 124                                          rwlock->__data.__shared);
 125 #endif
 126
 127       /* Get the lock.  */
 128       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 129
 130       /* To start over again, remove the thread from the writer list.  */
 131       --rwlock->__data.__nr_writers_queued;
 132
 133       /* Did the futex call time out?  */
 134       if (err == -ETIMEDOUT)
 135         {
 136           result = ETIMEDOUT;
 137           break;
 138         }
 139     }
 140
 141   /* We are done, free the lock.  */
 142   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 143
 144   return result;
 145 }