nptl/pthread_rwlock_wrlock.c

   1 /* Copyright (C) 2003,2007,2011 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 /* Acquire write lock for RWLOCK.  */
  27 int
  28 __pthread_rwlock_wrlock (rwlock)
  29      pthread_rwlock_t *rwlock;
  30 {
  31   int result = 0;
  32
  33   /* Make sure we are alone.  */
  34   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  35
  36   while (1)
  37     {
  38       /* Get the rwlock if there is no writer and no reader.  */
  39       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  40         {
  41           /* Mark self as writer.  */
  42           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  43           break;
  44         }
  45
  46       /* Make sure we are not holding the rwlock as a writer.  This is
  47          a deadlock situation we recognize and report.  */
  48       if (__builtin_expect (rwlock->__data.__writer
  49                             == THREAD_GETMEM (THREAD_SELF, tid), 0))
  50         {
  51           result = EDEADLK;
  52           break;
  53         }
  54
  55       /* Remember that we are a writer.  */
  56       if (++rwlock->__data.__nr_writers_queued == 0)
  57         {
  58           /* Overflow on number of queued writers.  */
  59           --rwlock->__data.__nr_writers_queued;
  60           result = EAGAIN;
  61           break;
  62         }
  63
  64       int waitval = rwlock->__data.__writer_wakeup;
  65
  66       /* Free the lock.  */
  67       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  68
  69       /* Wait for the writer or reader(s) to finish.  */
  70       lll_futex_wait (&rwlock->__data.__writer_wakeup, waitval,
  71                       rwlock->__data.__shared);
  72
  73       /* Get the lock.  */
  74       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  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_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  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)