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 <futex-internal.h>
  23 #include <pthread.h>
  24 #include <pthreadP.h>
  25 #include <stap-probe.h>
  26 #include <elide.h>
  27
  28
  29 /* Unlock RWLOCK.  */
  30 int
  31 __pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
  32 {
  33   int futex_shared =
  34       rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
  35
  36   LIBC_PROBE (rwlock_unlock, 1, rwlock);
  37
  38   if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
  39                     && rwlock->__data.__nr_readers == 0))
  40     return 0;
  41
  42   lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
  43   if (rwlock->__data.__writer)
  44     rwlock->__data.__writer = 0;
  45   else
  46     --rwlock->__data.__nr_readers;
  47   /* If there are still readers present, we do not yet need to wake writers
  48      nor are responsible to wake any readers.  */
  49   if (rwlock->__data.__nr_readers == 0)
  50     {
  51       /* Note that if there is a blocked writer, we effectively make it
  52          responsible for waking any readers because we don't wake readers in
  53          this case.  */
  54       if (rwlock->__data.__nr_writers_queued)
  55         {
  56           ++rwlock->__data.__writer_wakeup;
  57           lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  58           futex_wake (&rwlock->__data.__writer_wakeup, 1, futex_shared);
  59           return 0;
  60         }
  61       else if (rwlock->__data.__nr_readers_queued)
  62         {
  63           ++rwlock->__data.__readers_wakeup;
  64           lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  65           futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
  66                       futex_shared);
  67           return 0;
  68         }
  69     }
  70   lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
  71   return 0;
  72 }
  73
  74 weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock)
  75 hidden_def (__pthread_rwlock_unlock)