1 | /* Copyright (C) 2002-2016 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. |
3 | Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. |
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 "pthreadP.h" |
21 | #include <lowlevellock.h> |
22 | #include <futex-internal.h> |
23 | #include <elide.h> |
24 | #include <stdbool.h> |
25 | |
26 | |
27 | int |
28 | __pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock) |
29 | { |
30 | int result = EBUSY; |
31 | bool wake = false; |
32 | int futex_shared = |
33 | rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED; |
34 | |
35 | if (ELIDE_TRYLOCK (rwlock->__data.__rwelision, |
36 | rwlock->__data.__lock == 0 |
37 | && rwlock->__data.__nr_readers == 0 |
38 | && rwlock->__data.__writer, 0)) |
39 | return 0; |
40 | |
41 | lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); |
42 | |
43 | if (rwlock->__data.__writer == 0 |
44 | && (rwlock->__data.__nr_writers_queued == 0 |
45 | || PTHREAD_RWLOCK_PREFER_READER_P (rwlock))) |
46 | { |
47 | if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0)) |
48 | { |
49 | --rwlock->__data.__nr_readers; |
50 | result = EAGAIN; |
51 | } |
52 | else |
53 | { |
54 | result = 0; |
55 | /* See pthread_rwlock_rdlock. */ |
56 | if (rwlock->__data.__nr_readers == 1 |
57 | && rwlock->__data.__nr_readers_queued > 0 |
58 | && rwlock->__data.__nr_writers_queued > 0) |
59 | { |
60 | ++rwlock->__data.__readers_wakeup; |
61 | wake = true; |
62 | } |
63 | } |
64 | } |
65 | |
66 | lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); |
67 | |
68 | if (wake) |
69 | futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared); |
70 | |
71 | return result; |
72 | } |
73 | strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock) |
74 | |