1/* Copyright (C) 2003-2016 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. */
30int
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
74weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock)
75hidden_def (__pthread_rwlock_unlock)
76