nptl/pthread_rwlock_timedwrlock.c

   1 /* Copyright (C) 2003, 2004, 2007 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 write lock for RWLOCK or return after specfied time.  */
  28 int
  29 pthread_rwlock_timedwrlock (rwlock, abstime)
  30      pthread_rwlock_t *rwlock;
  31      const struct timespec *abstime;
  32 {
  33   int result = 0;
  34
  35   /* Make sure we are along.  */
  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 and no reader.  */
  43       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  44         {
  45           /* Mark self as writer.  */
  46           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  47           break;
  48         }
  49
  50       /* Make sure we are not holding the rwlock as a writer.  This is
  51          a deadlock situation we recognize and report.  */
  52       if (__builtin_expect (rwlock->__data.__writer
  53                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  54         {
  55           result = EDEADLK;
  56           break;
  57         }
  58
  59       /* Make sure the passed in timeout value is valid.  Ideally this
  60          test would be executed once.  But since it must not be
  61          performed if we would not block at all simply moving the test
  62          to the front is no option.  Replicating all the code is
  63          costly while this test is not.  */
  64       if (__builtin_expect (abstime->tv_nsec >= 1000000000
  65                             || abstime->tv_nsec < 0, 0))
  66         {
  67           result = EINVAL;
  68           break;
  69         }
  70
  71       /* Get the current time.  So far we support only one clock.  */
  72       struct timeval tv;
  73       (void) gettimeofday (&tv, NULL);
  74
  75       /* Convert the absolute timeout value to a relative timeout.  */
  76       struct timespec rt;
  77       rt.tv_sec = abstime->tv_sec - tv.tv_sec;
  78       rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
  79       if (rt.tv_nsec < 0)
  80         {
  81           rt.tv_nsec += 1000000000;
  82           --rt.tv_sec;
  83         }
  84       /* Did we already time out?  */
  85       if (rt.tv_sec < 0)
  86         {
  87           result = ETIMEDOUT;
  88           break;
  89         }
  90
  91       /* Remember that we are a writer.  */
  92       if (++rwlock->__data.__nr_writers_queued == 0)
  93         {
  94           /* Overflow on number of queued writers.  */
  95           --rwlock->__data.__nr_writers_queued;
  96           result = EAGAIN;
  97           break;
  98         }
  99
 100       int waitval = rwlock->__data.__writer_wakeup;
 101
 102       /* Free the lock.  */
 103       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 104
 105       /* Wait for the writer or reader(s) to finish.  */
 106       err = lll_futex_timed_wait (&rwlock->__data.__writer_wakeup,
 107                                   waitval, &rt, rwlock->__data.__shared);
 108
 109       /* Get the lock.  */
 110       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
 111
 112       /* To start over again, remove the thread from the writer list.  */
 113       --rwlock->__data.__nr_writers_queued;
 114
 115       /* Did the futex call time out?  */
 116       if (err == -ETIMEDOUT)
 117         {
 118           result = ETIMEDOUT;
 119           break;
 120         }
 121     }
 122
 123   /* We are done, free the lock.  */
 124   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
 125
 126   return result;
 127 }