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 "pthreadP.h" |
20 | #include <string.h> |
21 | #include <kernel-features.h> |
22 | |
23 | |
24 | static const struct pthread_rwlockattr default_rwlockattr = |
25 | { |
26 | .lockkind = PTHREAD_RWLOCK_DEFAULT_NP, |
27 | .pshared = PTHREAD_PROCESS_PRIVATE |
28 | }; |
29 | |
30 | |
31 | int |
32 | __pthread_rwlock_init (pthread_rwlock_t *rwlock, |
33 | const pthread_rwlockattr_t *attr) |
34 | { |
35 | const struct pthread_rwlockattr *iattr; |
36 | |
37 | iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_rwlockattr; |
38 | |
39 | memset (rwlock, '\0', sizeof (*rwlock)); |
40 | |
41 | rwlock->__data.__flags |
42 | = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP; |
43 | |
44 | /* The __SHARED field is computed to minimize the work that needs to |
45 | be done while handling the futex. There are two inputs: the |
46 | availability of private futexes and whether the rwlock is shared |
47 | or private. Unfortunately the value of a private rwlock is |
48 | fixed: it must be zero. The PRIVATE_FUTEX flag has the value |
49 | 0x80 in case private futexes are available and zero otherwise. |
50 | This leads to the following table: |
51 | |
52 | | pshared | result |
53 | | shared private | shared private | |
54 | ------------+-----------------+-----------------+ |
55 | !avail 0 | 0 0 | 0 0 | |
56 | avail 0x80 | 0x80 0 | 0 0x80 | |
57 | |
58 | If the pshared value is in locking functions XORed with avail |
59 | we get the expected result. */ |
60 | rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE |
61 | ? 0 : FUTEX_PRIVATE_FLAG); |
62 | |
63 | return 0; |
64 | } |
65 | strong_alias (__pthread_rwlock_init, pthread_rwlock_init) |
66 | |