nptl/pthread_rwlock_timedrdlock.c

   1 /* Copyright (C) 2003,2004,2007,2011 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <errno.h>
  21 #include <sysdep.h>
  22 #include <lowlevellock.h>
  23 #include <pthread.h>
  24 #include <pthreadP.h>
  25
  26
  27 /* Try to acquire read lock for RWLOCK or return after specfied time.  */
  28 int
  29 pthread_rwlock_timedrdlock (rwlock, abstime)
  30      pthread_rwlock_t *rwlock;
  31      const struct timespec *abstime;
  32 {
  33   int result = 0;
  34
  35   /* Make sure we are alone.  */
  36   lll_lock(rwlock->__data.__lock, rwlock->__data.__shared);
  37
  38   while (1)
  39     {
  40       int err;
  41
  42       /* Get the rwlock if there is no writer...  */
  43       if (rwlock->__data.__writer == 0
  44           /* ...and if either no writer is waiting or we prefer readers.  */
  45           && (!rwlock->__data.__nr_writers_queued
  46               || PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
  47         {
  48           /* Increment the reader counter.  Avoid overflow.  */
  49           if (++rwlock->__data.__nr_readers == 0)
  50             {
  51               /* Overflow on number of readers.  */
  52               --rwlock->__data.__nr_readers;
  53               result = EAGAIN;
  54             }
  55
  56           break;
  57         }
  58
  59       /* Make sure we are not holding the rwlock as a writer.  This is
  60          a deadlock situation we recognize and report.  */
  61       if (__builtin_expect (rwlock->__data.__writer
  62                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  63         {
  64           result = EDEADLK;
  65           break;
  66         }
  67
  68       /* Make sure the passed in timeout value is valid.  Ideally this
  69          test would be executed once.  But since it must not be
  70          performed if we would not block at all simply moving the test
  71          to the front is no option.  Replicating all the code is
  72          costly while this test is not.  */
  73       if (__builtin_expect (abstime->tv_nsec >= 1000000000
  74                             || abstime->tv_nsec < 0, 0))
  75         {
  76           result = EINVAL;
  77           break;
  78         }
  79
  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           /* Yep, return with an appropriate error.  */
  97           result = ETIMEDOUT;
  98           break;
  99         }
 100
 101       /* Remember that we are a reader.  */
 102       if (++rwlock->__data.__nr_readers_queued == 0)
 103         {
 104           /* Overflow on number of queued readers.  */
 105           --rwlock->__data.__nr_readers_queued;
 106           result = EAGAIN;
 107           break;
 108         }
 109
 110       int waitval = rwlock->__data.__readers_wakeup;
 111
 112       /* Free the lock.  */
 113       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 114
 115       /* Wait for the writer to finish.  */
 116       err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup,
 117                                   waitval, &rt, rwlock->__data.__shared);
 118
 119       /* Get the lock.  */
 120       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 121
 122       --rwlock->__data.__nr_readers_queued;
 123
 124       /* Did the futex call time out?  */
 125       if (err == -ETIMEDOUT)
 126         {
 127           /* Yep, report it.  */
 128           result = ETIMEDOUT;
 129           break;
 130         }
 131     }
 132
 133   /* We are done, free the lock.  */
 134   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 135
 136   return result;
 137 }