nptl/sysdeps/pthread/pthread_rwlock_wrlock.c

   1 /* Copyright (C) 2003 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 /* Acquire write lock for RWLOCK.  */
  28 int
  29 __pthread_rwlock_wrlock (rwlock)
  30      pthread_rwlock_t *rwlock;
  31 {
  32   int result = 0;
  33
  34   /* Make sure we are along.  */
  35   lll_mutex_lock (rwlock->__data.__lock);
  36
  37   while (1)
  38     {
  39       /* Get the rwlock if there is no writer and no reader.  */
  40       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  41         {
  42           /* Mark self as writer.  */
  43           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  44           break;
  45         }
  46
  47       /* Make sure we are not holding the rwlock as a writer.  This is
  48          a deadlock situation we recognize and report.  */
  49       if (__builtin_expect (rwlock->__data.__writer
  50                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  51         {
  52           result = EDEADLK;
  53           break;
  54         }
  55
  56       /* Remember that we are a writer.  */
  57       if (++rwlock->__data.__nr_writers_queued == 0)
  58         {
  59           /* Overflow on number of queued writers.  */
  60           --rwlock->__data.__nr_writers_queued;
  61           result = EAGAIN;
  62           break;
  63         }
  64
  65       int waitval = rwlock->__data.__writer_wakeup;
  66
  67       /* Free the lock.  */
  68       lll_mutex_unlock (rwlock->__data.__lock);
  69
  70       /* Wait for the writer or reader(s) to finish.  */
  71       lll_futex_wait (&rwlock->__data.__writer_wakeup, waitval);
  72
  73       /* Get the lock.  */
  74       lll_mutex_lock (rwlock->__data.__lock);
  75
  76       /* To start over again, remove the thread from the writer list.  */
  77       --rwlock->__data.__nr_writers_queued;
  78     }
  79
  80   /* We are done, free the lock.  */
  81   lll_mutex_unlock (rwlock->__data.__lock);
  82
  83   return result;
  84 }
  85
  86 weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
  87 strong_alias (__pthread_rwlock_wrlock, __pthread_rwlock_wrlock_internal)