fbtl/pthread_rwlock_wrlock.c

   1 /* Copyright (C) 2003-2013 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 #include <stap-probe.h>
  25
  26
  27 /* Acquire write lock for RWLOCK.  */
  28 int
  29 __pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
  30 {
  31   int result = 0;
  32
  33   LIBC_PROBE (wrlock_entry, 1, rwlock);
  34
  35   /* Make sure we are alone.  */
  36   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  37
  38   while (1)
  39     {
  40       /* Get the rwlock if there is no writer and no reader.  */
  41       if (rwlock->__data.__writer == 0 && rwlock->__data.__nr_readers == 0)
  42         {
  43           /* Mark self as writer.  */
  44           rwlock->__data.__writer = THREAD_GETMEM (THREAD_SELF, tid);
  45
  46           LIBC_PROBE (wrlock_acquire_write, 1, rwlock);
  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       /* Remember that we are a writer.  */
  60       if (++rwlock->__data.__nr_writers_queued == 0)
  61         {
  62           /* Overflow on number of queued writers.  */
  63           --rwlock->__data.__nr_writers_queued;
  64           result = EAGAIN;
  65           break;
  66         }
  67
  68       int waitval = rwlock->__data.__writer_wakeup;
  69
  70       /* Free the lock.  */
  71       lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  72
  73       /* Wait for the writer or reader(s) to finish.  */
  74       lll_futex_wait (&rwlock->__data.__writer_wakeup, waitval,
  75                       rwlock->__data.__shared);
  76
  77       /* Get the lock.  */
  78       lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  79
  80       /* To start over again, remove the thread from the writer list.  */
  81       --rwlock->__data.__nr_writers_queued;
  82     }
  83
  84   /* We are done, free the lock.  */
  85   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  86
  87   return result;
  88 }
  89
  90 weak_alias (__pthread_rwlock_wrlock, pthread_rwlock_wrlock)
  91 hidden_def (__pthread_rwlock_wrlock)