nptl/pthread_rwlock_unlock.c

   1 /* Copyright (C) 2003-2015 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 #include <elide.h>
  26
  27
  28 /* Unlock RWLOCK.  */
  29 int
  30 __pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
  31 {
  32   LIBC_PROBE (rwlock_unlock, 1, rwlock);
  33
  34   if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
  35                     && rwlock->__data.__nr_readers == 0))
  36     return 0;
  37
  38   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  39   if (rwlock->__data.__writer)
  40     rwlock->__data.__writer = 0;
  41   else
  42     --rwlock->__data.__nr_readers;
  43   /* If there are still readers present, we do not yet need to wake writers
  44      nor are responsible to wake any readers.  */
  45   if (rwlock->__data.__nr_readers == 0)
  46     {
  47       /* Note that if there is a blocked writer, we effectively make it
  48          responsible for waking any readers because we don't wake readers in
  49          this case.  */
  50       if (rwlock->__data.__nr_writers_queued)
  51         {
  52           ++rwlock->__data.__writer_wakeup;
  53           lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  54           lll_futex_wake (&rwlock->__data.__writer_wakeup, 1,
  55                           rwlock->__data.__shared);
  56           return 0;
  57         }
  58       else if (rwlock->__data.__nr_readers_queued)
  59         {
  60           ++rwlock->__data.__readers_wakeup;
  61           lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  62           lll_futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
  63                           rwlock->__data.__shared);
  64           return 0;
  65         }
  66     }
  67   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  68   return 0;
  69 }
  70
  71 weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock)
  72 hidden_def (__pthread_rwlock_unlock)