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, 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       /* Get the current time.  So far we support only one clock.  */
  80       struct timeval tv;
  81       (void) gettimeofday (&tv, NULL);
  82
  83       /* Convert the absolute timeout value to a relative timeout.  */
  84       struct timespec rt;
  85       rt.tv_sec = abstime->tv_sec - tv.tv_sec;
  86       rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
  87       if (rt.tv_nsec < 0)
  88         {
  89           rt.tv_nsec += 1000000000;
  90           --rt.tv_sec;
  91         }
  92       /* Did we already time out?  */
  93       if (rt.tv_sec < 0)
  94         {
  95           /* Yep, return with an appropriate error.  */
  96           result = ETIMEDOUT;
  97           break;
  98         }
  99
 100       /* Remember that we are a reader.  */
 101       if (++rwlock->__data.__nr_readers_queued == 0)
 102         {
 103           /* Overflow on number of queued readers.  */
 104           --rwlock->__data.__nr_readers_queued;
 105           result = EAGAIN;
 106           break;
 107         }
 108
 109       int waitval = rwlock->__data.__readers_wakeup;
 110
 111       /* Free the lock.  */
 112       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 113
 114       /* Wait for the writer to finish.  */
 115       err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup,
 116                                   waitval, &rt, rwlock->__data.__shared);
 117
 118       /* Get the lock.  */
 119       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 120
 121       --rwlock->__data.__nr_readers_queued;
 122
 123       /* Did the futex call time out?  */
 124       if (err == -ETIMEDOUT)
 125         {
 126           /* Yep, report it.  */
 127           result = ETIMEDOUT;
 128           break;
 129         }
 130     }
 131
 132   /* We are done, free the lock.  */
 133   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 134
 135   return result;
 136 }